[PATCH] doc: Add documentation about devicetree usage

[PATCH] doc: Add documentation about devicetree usage

[Simon Glass]

At present some of the ideas and techniques behind devicetree in U-Boot
are assumed, implied or unsaid. Add some documentation to cover how
devicetree is build, how it can be modified and the rules about using
the various CONFIG_OF_... options.

Signed-off-by: Simon Glass <sjg@chromium.org>
---

 doc/develop/index.rst              |   1 +
 doc/develop/package/devicetree.rst | 315 +++++++++++++++++++++++++++++
 doc/develop/package/index.rst      |   1 +
 3 files changed, 317 insertions(+)
 create mode 100644 doc/develop/package/devicetree.rst

diff --git a/doc/develop/index.rst b/doc/develop/index.rst
index 83c929babda..d5ad8f9fe53 100644
--- a/doc/develop/index.rst
+++ b/doc/develop/index.rst
@@ -36,6 +36,7 @@ Packaging
    :maxdepth: 1
 
    package/index
+   package/devicetree
 
 Testing
 -------
diff --git a/doc/develop/package/devicetree.rst b/doc/develop/package/devicetree.rst
new file mode 100644
index 00000000000..fccbb182f3e
--- /dev/null
+++ b/doc/develop/package/devicetree.rst
@@ -0,0 +1,315 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+Updating the devicetree
+=======================
+
+U-Boot uses devicetree for runtime configuration and storing required blobs or
+any other information it needs to operate. It is possible to update the
+devicetree separately from actually building U-Boot. This provides a good degree
+of control and flexibility for firmware that uses U-Boot in conjunction with
+other project.
+
+There are many reasons why it is useful to modify the devicetree after building
+it:
+
+- Configuration can be changed, e.g. which UART to use
+- A serial number can be added
+- Public keys can be added to allow image verification
+- Console output can be changed (e.g. to select serial or vidconsole)
+
+This section describes how to work with devicetree to accomplish your goals.
+
+See also :doc:`../devicetree/control` for a basic summary of the available
+features.
+
+
+Devicetree source
+-----------------
+
+Every board in U-Boot must include a devicetree sufficient to build and boot
+that board on suitable hardware (or emulation). This is specified using the
+`CONFIG DEFAULT_DEVICE_TREE` option.
+
+
+Current situation (August 2021)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+As an aside, at present U-Boot allows `CONFIG_DEFAULT_DEVICE_TREE` to be empty,
+e.g. if `CONFIG_OF_BOARD` or `CONFIG_OF_PRIOR_STAGE` are used. This has
+unfortunately created an enormous amount of confusion and some wasted effort.
+This was not intended and this bug will be fixed soon. Specifically:
+
+- `CONFIG_OF_BOARD` was added in rpi_patch_ for Raspberry Pi, which does have
+  an in-tree devicetree, but this feature has since been used for boards that
+  don't
+- `CONFIG_OF_PRIOR_STAGE` was added in bcm_patch_ as part of a larger Broadcom
+  change with a tag indicating it only affected one board, so the change in
+  behaviour was not noticed at the time. It has since been used by RISC-V qemu
+  boards.
+
+Once this bug is fixed, CONFIG_OF_BOARD and CONFIG_OF_PRIOR_STAGE will override
+(at runtime) the devicetree suppled with U-Boot, but will otherwise use
+CONFIG_OF_SEPARATE for the in-tree build. So these two will become options,
+moving out of the 'choice' in `dts/Kconfig`
+
+Offending boards are:
+
+- bcm7260
+- bcm7445
+- qemu_arm64
+- qemu_arm
+- qemu-ppce500
+- qemu-riscv32
+- qemu-riscv32_smode
+- qemu-riscv64
+- qemu-riscv64_smode
+
+All of these need to have a devicetree added in-tree. This is targeted to be
+fixed in the 2022.01 release.
+
+
+Building the devicetree
+-----------------------
+
+U-Boot automatically builds the devicetree for a board, from the
+`arch/<arch>/dts` directory. The Makefile in those directories has rules for
+building devicetree files. It is preferable to avoid target-specific rules in
+those files: i.e. all boards for a particular SoC should be built at once,
+where practical. Apart from simplifying the Makefile, this helps to efficiently
+(and immediately) ensure that changes in one board's DT do not break others that
+are related. Building devicetrees is fast, so performance is seldom a concern
+here.
+
+
+Overriding the default devicetree
+---------------------------------
+
+When building U-Boot, the `DEVICE_TREE` environment variable allows the
+default devicetree file to be overridden at build time. This can be useful if
+modifications have to be made to the in-tree devicetree file, for the benefit
+of a downstream build system. Note that the in-tree devicetree must be
+sufficient to build and boot, so this is not a way to bypass that requirement.
+
+
+Modifying the devicetree after building
+---------------------------------------
+
+While it is generally painful and hacky to modify the code or rodata of a
+program after it is built, in many cases it is useul to do so, e.g. to add
+configuration information like serial numbers, enabling/disabling features, etc.
+
+Devicetree provides a very nice solution to these problems since it is
+structured data and it is relatively easy to change it, even in binary form
+(see fdtput).
+
+U-Boot takes care that the devicetree is easily accessible after the build
+process. In fact it is placed in a separate file called `u-boot.dtb`. If the
+build system wants to modify or replace that file, it can do so. Then all that
+is needed is to run `binman update` to update the file inside the image. If
+binman is not used, then `u-boot-nodtb.bin` and the new `u-boot.dtb` can simply
+be concatenated to achieve the desired result. U-Boot happily copes with the
+devicetree growing or shrinking.
+
+The `u-boot.bin` image contains both pieces. While it is possible to locate the
+devicetree within the image using the signature at the start of the file, this
+is a bit messy.
+
+This is why `CONFIG_OF_SEPARATE` should always be used when building U-Boot.
+The `CONFIG_OF_EMBED` option embeds the devicetree somewhere in the U-Boot ELF
+image as rodata, meaning that it is hard to find it and it cannot increase in
+size.
+
+When modifying the devicetree, the different cases to consider are as follows:
+
+- CONFIG_OF_SEPARATE
+    This is easy, described above. Just change, replace or rebuild the
+    devicetree so it suits your needs, then rerun binman or redo the `cat`
+    operation to join `u-boot-nodtb.bin` and the new `u-boot.dtb`
+
+- CONFIG_OF_EMBD
+    This is tricky, since the devicetree cannot easily be located. If the EFL
+    file is available, then the _dtb_dt_begin and __dtb_dt_end symbols can be
+    examined to find it. While it is possible to contract the file, it is not
+    possible to expand the file since that would involve re-linking
+
+- CONFIG_OF_PRIOR_STAGE
+    In this case the devicetree must be modified in the project which provides
+    it, as described below
+
+- CONFIG_OF_BOARD
+    This is a board-specific situation, so needs to be considered on a
+    case-by-case base. The devicetree must be modified so that the correct
+    one is provided to U-Boot. How this is done depends entirely on the
+    implementation of this option for the board. It might require injecting the
+    changes into a different project somehow using tooling available there, or
+    it might involve merging an overlay file at runtime to obtain the desired
+    result.
+
+
+Devicetree in another project
+-----------------------------
+
+In some cases U-Boot receive its devicetree at runtime from a program that calls
+it. For example ARM's Trusted Firmware A (`TF-A`_) may have a devicetree that it
+passes to U-Boot. This overrides any devicetree build by U-Boot. When packaging
+the firmware, the U-Boot devicetree may in fact be left out if it can be
+guaranteed that it will receive one from another project.
+
+In this case, the devicetree in the other project must track U-Boot's use of
+device tree. It must provide a way to add configuration and other information to
+the devicetree for use by U-Boot, such as the /config node. Note that the
+U-Boot in-tree devicetree must be sufficient to build and boot, so this is not a
+way to bypass that requirement.
+
+If binman is used, the in-tree U-Boot devicetree must contain the binman
+definition so that a valid image can be build.
+
+If verified boot is used, the project must provide a way to inject a public key,
+certificate or other material into the U-Boot devicetree so that it is available
+to U-Boot at runtime. See `Signing with U-Boot devicetree`_. This may be
+through tooling in the project itself or by making use of U-Boot's tooling.
+
+
+Devicetree generated on-the-fly in another project
+--------------------------------------------------
+
+In some rare cases, another project may wish to create a devicetree for U-Boot
+entirely on-the-fly, then pass it to U-Boot at runtime. The only known example
+of this at the time of writing (2021) is qemu, for ARM (`QEMU ARM`_) and
+RISC-V (`QEMU RISC-V`_).
+
+In this case, the devicetree in the other project must track U-Boot's use of
+device tree, so that it remains compatible. If a particular version of the
+project is needed for a particular version of U-Boot, that must be documented
+in both projects.
+
+Further, it must provide a way to add configuration and other information to
+the devicetree for use by U-Boot, such as the `/config` node. Note that the
+U-Boot in-tree devicetree must be sufficient to build and boot, so this is not a
+way to bypass that requirement.
+
+More specifically, tooling or command-line arguments must provide a way to
+add a `/config` node or items within that node, so that U-Boot can receive a
+suitable configuration. These options can then be used as part of the build
+process, which puts the firmware image together. For binman, a way must be
+provided to add the binman definition into the devicetree in the same way.
+
+One way to do this is to allow a .dtsi file to be merged in with the generated
+devicetree.
+
+
+Passing the devicetree through to Linux
+---------------------------------------
+
+Ideally U-Boot and Linux use the same devicetree source, even though it is
+hosted in separate projects. U-Boot adds some extra pieces, such as the
+`config/` node and tags like `u-boot,dm-spl`. Linux adds some extra pieces, such
+as `linux,default-trigger` and `linux,code`. This should not interfere with
+each other.
+
+In principle it is possible for U-Boot's control devicetree to be passed to
+Linux. This is, after all, one of the goals of devicetree and the original
+Open Firmware project, to have the firmware provide the hardware description to
+the Operating System.
+
+For boards where this approach is used, care must be taken. U-Boot typically
+needs to 'fix up' the devicetree before passing it to Linux, e.g. to add
+information about the memory map, about which serial console is used, provide
+the root hash for dm-verify or select whether the console should be silenced for
+a faster boot.
+
+Fix-ups involve modifying the devicetree. If the control devicetree is used,
+that means the control devicetree could be modified, while U-Boot is using it.
+Removing a device and reinserting it can cause problems if the devicetree offset
+has changed, for example, since the device will be unable to locates its
+devicetree properties at the expected devicetree offset, which is a fixed
+integer.
+
+To deal with this, it is recommended to employ one or more of the following
+approaches:
+
+- Make a copy of the devicetree and 'fix up' the copy, leaving the control
+  devicetree alone
+- Enable `CONFIG_OF_LIVE` so that U-Boot makes its own copy of the devicetree
+  during relocation; fixups then happen on the original flat tree
+- Ensure that fix-ups happen after all loading has happened and U-Boot has
+  completed image verification
+
+In practice,the last point is typically observed, since boot_prep_linux() is
+called just before jumping to Linux, long after signature verification, for
+example. But it is important to make sure that this line is not blurred,
+particularly if untrusted user data in involved.
+
+
+Devicetree use cases that must be supported
+-------------------------------------------
+
+Regardless of how the devicetree is provided to U-Boot at runtime, various
+U-Boot features must be fully supported. This section describes some of these
+features and the implications for other projects.
+
+If U-Boot uses its own in-tree devicetree these features are supported
+automatically.
+
+
+Signing with U-Boot devicetree
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+U-Boot supports signing a payload so that it can be verified to have been
+created by a party owning a private key. This is called verified boot in U-Boot
+(see doc/uImage.FIT/verified-boot.txt).
+
+Typically this works by creating a FIT and then running the `mkimage` tool to
+add signatures for particular images. As part of this process, `mkimage` writes
+a public key to the U-Boot devicetree, although this can be done separately.
+
+As with all configuration information, if another project is providing the
+devicetree to U-Boot, it must provide a way to add this public key into the
+devicetree it passes to U-Boot. This could be via a tooling option, making use
+of `mkimage`, or alowing a .dtsi file to be merged in with what is generated in
+the other project.
+
+
+Providing the binman image definition
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+In complex systems U-Boot must locate and make use of other firmware components,
+such as images for the user interface, files containing peripheral firmware,
+multiple copies of U-Boot for use with A/B boot, etc. U-Boot uses
+:doc:`Binman <binman>` as a standard way of putting an image together.
+
+Typically this works by running binman with the devicetree as an input, to
+create the file image. Binman then outputs an updated devicetree which is
+packed in the firmware image, so U-Boot can access the binman definition and
+locate all the components.
+
+As with all configuration information, if another project is providing the
+devicetree to U-Boot, it must provide a way to add this binman definition into
+the devicetree it passes to U-Boot. This could be via a tooling option, making
+use of `binman`, or alowing a .dtsi file to be merged in with what is generated
+in the other project.
+
+
+Protecting the devicetree
+-------------------------
+
+U-Boot relies heavily on devicetree for correct operation. A corrupt or invalid
+device can cause U-Boot to fail to start, behave incorrectly, crash (e.g. if
+`CONFIG_OF_LIBFDT_ASSUME_MASK` is adjusted, or fail to boot an Operating System.
+Within U-Boot, the devicetree is as important as any other part of the source
+code. At ruuntime, the devicetree can be considered to be structured rodata.
+
+With secure systems, care must be taken that the devicetree is valid:
+
+- If the code / rodata has a hash or signature, the devicetree should also, if
+  they are packaged separately.
+- If the code / rodata is write-protected when running, the devicetree should be
+  also. Note that U-Boot relocates its code and devicetree, so this is not as
+  simple as it sounds. U-Boot must write-protect these items after relocating.
+
+
+.. _rpi_patch: https://patchwork.ozlabs.org/project/uboot/patch/20170402082520.32546-1-deymo@google.com/
+.. _bcm_patch: https://patchwork.ozlabs.org/project/uboot/patch/16fc0901f4521d3c399eac950c52a634b2f9473b.1528485916.git.fitzsim@fitzsim.org/
+.. _`TF-A`: https://www.trustedfirmware.org/projects/tf-a
+.. _`QEMU ARM`: https://github.com/qemu/qemu/blob/master/hw/arm/virt.c
+.. _`QEMU RISC-V`: https://github.com/qemu/qemu/blob/master/hw/riscv/virt.c
diff --git a/doc/develop/package/index.rst b/doc/develop/package/index.rst
index 9374be2e62c..188c376950e 100644
--- a/doc/develop/package/index.rst
+++ b/doc/develop/package/index.rst
@@ -17,3 +17,4 @@ SPI flash.
    :maxdepth: 2
 
    binman
+   devicetree
-- 
2.33.0.259.gc128427fd7-goog

Re: [PATCH] doc: Add documentation about devicetree usage

[Simon Glass]

+Ilias Apalodimas

On Fri, 27 Aug 2021 at 21:23, Simon Glass <sjg@chromium.org> wrote:
>
> At present some of the ideas and techniques behind devicetree in U-Boot
> are assumed, implied or unsaid. Add some documentation to cover how
> devicetree is build, how it can be modified and the rules about using
> the various CONFIG_OF_... options.
>
> Signed-off-by: Simon Glass <sjg@chromium.org>
> ---
>
>  doc/develop/index.rst              |   1 +
>  doc/develop/package/devicetree.rst | 315 +++++++++++++++++++++++++++++
>  doc/develop/package/index.rst      |   1 +
>  3 files changed, 317 insertions(+)
>  create mode 100644 doc/develop/package/devicetree.rst
>
> diff --git a/doc/develop/index.rst b/doc/develop/index.rst
> index 83c929babda..d5ad8f9fe53 100644
> --- a/doc/develop/index.rst
> +++ b/doc/develop/index.rst
> @@ -36,6 +36,7 @@ Packaging
>     :maxdepth: 1
>
>     package/index
> +   package/devicetree
>
>  Testing
>  -------
> diff --git a/doc/develop/package/devicetree.rst b/doc/develop/package/devicetree.rst
> new file mode 100644
> index 00000000000..fccbb182f3e
> --- /dev/null
> +++ b/doc/develop/package/devicetree.rst
> @@ -0,0 +1,315 @@
> +.. SPDX-License-Identifier: GPL-2.0+
> +
> +Updating the devicetree
> +=======================
> +
> +U-Boot uses devicetree for runtime configuration and storing required blobs or
> +any other information it needs to operate. It is possible to update the
> +devicetree separately from actually building U-Boot. This provides a good degree
> +of control and flexibility for firmware that uses U-Boot in conjunction with
> +other project.
> +
> +There are many reasons why it is useful to modify the devicetree after building
> +it:
> +
> +- Configuration can be changed, e.g. which UART to use
> +- A serial number can be added
> +- Public keys can be added to allow image verification
> +- Console output can be changed (e.g. to select serial or vidconsole)
> +
> +This section describes how to work with devicetree to accomplish your goals.
> +
> +See also :doc:`../devicetree/control` for a basic summary of the available
> +features.
> +
> +
> +Devicetree source
> +-----------------
> +
> +Every board in U-Boot must include a devicetree sufficient to build and boot
> +that board on suitable hardware (or emulation). This is specified using the
> +`CONFIG DEFAULT_DEVICE_TREE` option.
> +
> +
> +Current situation (August 2021)
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +As an aside, at present U-Boot allows `CONFIG_DEFAULT_DEVICE_TREE` to be empty,
> +e.g. if `CONFIG_OF_BOARD` or `CONFIG_OF_PRIOR_STAGE` are used. This has
> +unfortunately created an enormous amount of confusion and some wasted effort.
> +This was not intended and this bug will be fixed soon. Specifically:
> +
> +- `CONFIG_OF_BOARD` was added in rpi_patch_ for Raspberry Pi, which does have
> +  an in-tree devicetree, but this feature has since been used for boards that
> +  don't
> +- `CONFIG_OF_PRIOR_STAGE` was added in bcm_patch_ as part of a larger Broadcom
> +  change with a tag indicating it only affected one board, so the change in
> +  behaviour was not noticed at the time. It has since been used by RISC-V qemu
> +  boards.
> +
> +Once this bug is fixed, CONFIG_OF_BOARD and CONFIG_OF_PRIOR_STAGE will override
> +(at runtime) the devicetree suppled with U-Boot, but will otherwise use
> +CONFIG_OF_SEPARATE for the in-tree build. So these two will become options,
> +moving out of the 'choice' in `dts/Kconfig`
> +
> +Offending boards are:
> +
> +- bcm7260
> +- bcm7445
> +- qemu_arm64
> +- qemu_arm
> +- qemu-ppce500
> +- qemu-riscv32
> +- qemu-riscv32_smode
> +- qemu-riscv64
> +- qemu-riscv64_smode
> +
> +All of these need to have a devicetree added in-tree. This is targeted to be
> +fixed in the 2022.01 release.
> +
> +
> +Building the devicetree
> +-----------------------
> +
> +U-Boot automatically builds the devicetree for a board, from the
> +`arch/<arch>/dts` directory. The Makefile in those directories has rules for
> +building devicetree files. It is preferable to avoid target-specific rules in
> +those files: i.e. all boards for a particular SoC should be built at once,
> +where practical. Apart from simplifying the Makefile, this helps to efficiently
> +(and immediately) ensure that changes in one board's DT do not break others that
> +are related. Building devicetrees is fast, so performance is seldom a concern
> +here.
> +
> +
> +Overriding the default devicetree
> +---------------------------------
> +
> +When building U-Boot, the `DEVICE_TREE` environment variable allows the
> +default devicetree file to be overridden at build time. This can be useful if
> +modifications have to be made to the in-tree devicetree file, for the benefit
> +of a downstream build system. Note that the in-tree devicetree must be
> +sufficient to build and boot, so this is not a way to bypass that requirement.
> +
> +
> +Modifying the devicetree after building
> +---------------------------------------
> +
> +While it is generally painful and hacky to modify the code or rodata of a
> +program after it is built, in many cases it is useul to do so, e.g. to add
> +configuration information like serial numbers, enabling/disabling features, etc.
> +
> +Devicetree provides a very nice solution to these problems since it is
> +structured data and it is relatively easy to change it, even in binary form
> +(see fdtput).
> +
> +U-Boot takes care that the devicetree is easily accessible after the build
> +process. In fact it is placed in a separate file called `u-boot.dtb`. If the
> +build system wants to modify or replace that file, it can do so. Then all that
> +is needed is to run `binman update` to update the file inside the image. If
> +binman is not used, then `u-boot-nodtb.bin` and the new `u-boot.dtb` can simply
> +be concatenated to achieve the desired result. U-Boot happily copes with the
> +devicetree growing or shrinking.
> +
> +The `u-boot.bin` image contains both pieces. While it is possible to locate the
> +devicetree within the image using the signature at the start of the file, this
> +is a bit messy.
> +
> +This is why `CONFIG_OF_SEPARATE` should always be used when building U-Boot.
> +The `CONFIG_OF_EMBED` option embeds the devicetree somewhere in the U-Boot ELF
> +image as rodata, meaning that it is hard to find it and it cannot increase in
> +size.
> +
> +When modifying the devicetree, the different cases to consider are as follows:
> +
> +- CONFIG_OF_SEPARATE
> +    This is easy, described above. Just change, replace or rebuild the
> +    devicetree so it suits your needs, then rerun binman or redo the `cat`
> +    operation to join `u-boot-nodtb.bin` and the new `u-boot.dtb`
> +
> +- CONFIG_OF_EMBD
> +    This is tricky, since the devicetree cannot easily be located. If the EFL
> +    file is available, then the _dtb_dt_begin and __dtb_dt_end symbols can be
> +    examined to find it. While it is possible to contract the file, it is not
> +    possible to expand the file since that would involve re-linking
> +
> +- CONFIG_OF_PRIOR_STAGE
> +    In this case the devicetree must be modified in the project which provides
> +    it, as described below
> +
> +- CONFIG_OF_BOARD
> +    This is a board-specific situation, so needs to be considered on a
> +    case-by-case base. The devicetree must be modified so that the correct
> +    one is provided to U-Boot. How this is done depends entirely on the
> +    implementation of this option for the board. It might require injecting the
> +    changes into a different project somehow using tooling available there, or
> +    it might involve merging an overlay file at runtime to obtain the desired
> +    result.
> +
> +
> +Devicetree in another project
> +-----------------------------
> +
> +In some cases U-Boot receive its devicetree at runtime from a program that calls
> +it. For example ARM's Trusted Firmware A (`TF-A`_) may have a devicetree that it
> +passes to U-Boot. This overrides any devicetree build by U-Boot. When packaging
> +the firmware, the U-Boot devicetree may in fact be left out if it can be
> +guaranteed that it will receive one from another project.
> +
> +In this case, the devicetree in the other project must track U-Boot's use of
> +device tree. It must provide a way to add configuration and other information to
> +the devicetree for use by U-Boot, such as the /config node. Note that the
> +U-Boot in-tree devicetree must be sufficient to build and boot, so this is not a
> +way to bypass that requirement.
> +
> +If binman is used, the in-tree U-Boot devicetree must contain the binman
> +definition so that a valid image can be build.
> +
> +If verified boot is used, the project must provide a way to inject a public key,
> +certificate or other material into the U-Boot devicetree so that it is available
> +to U-Boot at runtime. See `Signing with U-Boot devicetree`_. This may be
> +through tooling in the project itself or by making use of U-Boot's tooling.
> +
> +
> +Devicetree generated on-the-fly in another project
> +--------------------------------------------------
> +
> +In some rare cases, another project may wish to create a devicetree for U-Boot
> +entirely on-the-fly, then pass it to U-Boot at runtime. The only known example
> +of this at the time of writing (2021) is qemu, for ARM (`QEMU ARM`_) and
> +RISC-V (`QEMU RISC-V`_).
> +
> +In this case, the devicetree in the other project must track U-Boot's use of
> +device tree, so that it remains compatible. If a particular version of the
> +project is needed for a particular version of U-Boot, that must be documented
> +in both projects.
> +
> +Further, it must provide a way to add configuration and other information to
> +the devicetree for use by U-Boot, such as the `/config` node. Note that the
> +U-Boot in-tree devicetree must be sufficient to build and boot, so this is not a
> +way to bypass that requirement.
> +
> +More specifically, tooling or command-line arguments must provide a way to
> +add a `/config` node or items within that node, so that U-Boot can receive a
> +suitable configuration. These options can then be used as part of the build
> +process, which puts the firmware image together. For binman, a way must be
> +provided to add the binman definition into the devicetree in the same way.
> +
> +One way to do this is to allow a .dtsi file to be merged in with the generated
> +devicetree.
> +
> +
> +Passing the devicetree through to Linux
> +---------------------------------------
> +
> +Ideally U-Boot and Linux use the same devicetree source, even though it is
> +hosted in separate projects. U-Boot adds some extra pieces, such as the
> +`config/` node and tags like `u-boot,dm-spl`. Linux adds some extra pieces, such
> +as `linux,default-trigger` and `linux,code`. This should not interfere with
> +each other.
> +
> +In principle it is possible for U-Boot's control devicetree to be passed to
> +Linux. This is, after all, one of the goals of devicetree and the original
> +Open Firmware project, to have the firmware provide the hardware description to
> +the Operating System.
> +
> +For boards where this approach is used, care must be taken. U-Boot typically
> +needs to 'fix up' the devicetree before passing it to Linux, e.g. to add
> +information about the memory map, about which serial console is used, provide
> +the root hash for dm-verify or select whether the console should be silenced for
> +a faster boot.
> +
> +Fix-ups involve modifying the devicetree. If the control devicetree is used,
> +that means the control devicetree could be modified, while U-Boot is using it.
> +Removing a device and reinserting it can cause problems if the devicetree offset
> +has changed, for example, since the device will be unable to locates its
> +devicetree properties at the expected devicetree offset, which is a fixed
> +integer.
> +
> +To deal with this, it is recommended to employ one or more of the following
> +approaches:
> +
> +- Make a copy of the devicetree and 'fix up' the copy, leaving the control
> +  devicetree alone
> +- Enable `CONFIG_OF_LIVE` so that U-Boot makes its own copy of the devicetree
> +  during relocation; fixups then happen on the original flat tree
> +- Ensure that fix-ups happen after all loading has happened and U-Boot has
> +  completed image verification
> +
> +In practice,the last point is typically observed, since boot_prep_linux() is
> +called just before jumping to Linux, long after signature verification, for
> +example. But it is important to make sure that this line is not blurred,
> +particularly if untrusted user data in involved.
> +
> +
> +Devicetree use cases that must be supported
> +-------------------------------------------
> +
> +Regardless of how the devicetree is provided to U-Boot at runtime, various
> +U-Boot features must be fully supported. This section describes some of these
> +features and the implications for other projects.
> +
> +If U-Boot uses its own in-tree devicetree these features are supported
> +automatically.
> +
> +
> +Signing with U-Boot devicetree
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +U-Boot supports signing a payload so that it can be verified to have been
> +created by a party owning a private key. This is called verified boot in U-Boot
> +(see doc/uImage.FIT/verified-boot.txt).
> +
> +Typically this works by creating a FIT and then running the `mkimage` tool to
> +add signatures for particular images. As part of this process, `mkimage` writes
> +a public key to the U-Boot devicetree, although this can be done separately.
> +
> +As with all configuration information, if another project is providing the
> +devicetree to U-Boot, it must provide a way to add this public key into the
> +devicetree it passes to U-Boot. This could be via a tooling option, making use
> +of `mkimage`, or alowing a .dtsi file to be merged in with what is generated in
> +the other project.
> +
> +
> +Providing the binman image definition
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +In complex systems U-Boot must locate and make use of other firmware components,
> +such as images for the user interface, files containing peripheral firmware,
> +multiple copies of U-Boot for use with A/B boot, etc. U-Boot uses
> +:doc:`Binman <binman>` as a standard way of putting an image together.
> +
> +Typically this works by running binman with the devicetree as an input, to
> +create the file image. Binman then outputs an updated devicetree which is
> +packed in the firmware image, so U-Boot can access the binman definition and
> +locate all the components.
> +
> +As with all configuration information, if another project is providing the
> +devicetree to U-Boot, it must provide a way to add this binman definition into
> +the devicetree it passes to U-Boot. This could be via a tooling option, making
> +use of `binman`, or alowing a .dtsi file to be merged in with what is generated
> +in the other project.
> +
> +
> +Protecting the devicetree
> +-------------------------
> +
> +U-Boot relies heavily on devicetree for correct operation. A corrupt or invalid
> +device can cause U-Boot to fail to start, behave incorrectly, crash (e.g. if
> +`CONFIG_OF_LIBFDT_ASSUME_MASK` is adjusted, or fail to boot an Operating System.
> +Within U-Boot, the devicetree is as important as any other part of the source
> +code. At ruuntime, the devicetree can be considered to be structured rodata.
> +
> +With secure systems, care must be taken that the devicetree is valid:
> +
> +- If the code / rodata has a hash or signature, the devicetree should also, if
> +  they are packaged separately.
> +- If the code / rodata is write-protected when running, the devicetree should be
> +  also. Note that U-Boot relocates its code and devicetree, so this is not as
> +  simple as it sounds. U-Boot must write-protect these items after relocating.
> +
> +
> +.. _rpi_patch: https://patchwork.ozlabs.org/project/uboot/patch/20170402082520.32546-1-deymo@google.com/
> +.. _bcm_patch: https://patchwork.ozlabs.org/project/uboot/patch/16fc0901f4521d3c399eac950c52a634b2f9473b.1528485916.git.fitzsim@fitzsim.org/
> +.. _`TF-A`: https://www.trustedfirmware.org/projects/tf-a
> +.. _`QEMU ARM`: https://github.com/qemu/qemu/blob/master/hw/arm/virt.c
> +.. _`QEMU RISC-V`: https://github.com/qemu/qemu/blob/master/hw/riscv/virt.c
> diff --git a/doc/develop/package/index.rst b/doc/develop/package/index.rst
> index 9374be2e62c..188c376950e 100644
> --- a/doc/develop/package/index.rst
> +++ b/doc/develop/package/index.rst
> @@ -17,3 +17,4 @@ SPI flash.
>     :maxdepth: 2
>
>     binman
> +   devicetree
> --
> 2.33.0.259.gc128427fd7-goog
>

Re: [PATCH] doc: Add documentation about devicetree usage

[Sean Anderson]

On 8/27/21 11:23 PM, Simon Glass wrote:
> At present some of the ideas and techniques behind devicetree in U-Boot
> are assumed, implied or unsaid. Add some documentation to cover how
> devicetree is build, how it can be modified and the rules about using
> the various CONFIG_OF_... options.
> 
> Signed-off-by: Simon Glass <sjg@chromium.org>
> ---
> 
>   doc/develop/index.rst              |   1 +
>   doc/develop/package/devicetree.rst | 315 +++++++++++++++++++++++++++++
>   doc/develop/package/index.rst      |   1 +
>   3 files changed, 317 insertions(+)
>   create mode 100644 doc/develop/package/devicetree.rst
> 
> diff --git a/doc/develop/index.rst b/doc/develop/index.rst
> index 83c929babda..d5ad8f9fe53 100644
> --- a/doc/develop/index.rst
> +++ b/doc/develop/index.rst
> @@ -36,6 +36,7 @@ Packaging
>      :maxdepth: 1
>   
>      package/index
> +   package/devicetree
>   
>   Testing
>   -------
> diff --git a/doc/develop/package/devicetree.rst b/doc/develop/package/devicetree.rst
> new file mode 100644
> index 00000000000..fccbb182f3e
> --- /dev/null
> +++ b/doc/develop/package/devicetree.rst
> @@ -0,0 +1,315 @@
> +.. SPDX-License-Identifier: GPL-2.0+
> +
> +Updating the devicetree
> +=======================
> +
> +U-Boot uses devicetree for runtime configuration and storing required blobs or
> +any other information it needs to operate. It is possible to update the
> +devicetree separately from actually building U-Boot. This provides a good degree
> +of control and flexibility for firmware that uses U-Boot in conjunction with
> +other project.

nit: projects

> +
> +There are many reasons why it is useful to modify the devicetree after building
> +it:
> +
> +- Configuration can be changed, e.g. which UART to use
> +- A serial number can be added
> +- Public keys can be added to allow image verification
> +- Console output can be changed (e.g. to select serial or vidconsole)
> +
> +This section describes how to work with devicetree to accomplish your goals.
> +
> +See also :doc:`../devicetree/control` for a basic summary of the available
> +features.
> +
> +
> +Devicetree source
> +-----------------
> +
> +Every board in U-Boot must include a devicetree sufficient to build and boot
> +that board on suitable hardware (or emulation). This is specified using the
> +`CONFIG DEFAULT_DEVICE_TREE` option.
> +
> +
> +Current situation (August 2021)
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +As an aside, at present U-Boot allows `CONFIG_DEFAULT_DEVICE_TREE` to be empty,
> +e.g. if `CONFIG_OF_BOARD` or `CONFIG_OF_PRIOR_STAGE` are used. This has
> +unfortunately created an enormous amount of confusion and some wasted effort.
> +This was not intended and this bug will be fixed soon. Specifically:
> +
> +- `CONFIG_OF_BOARD` was added in rpi_patch_ for Raspberry Pi, which does have
> +  an in-tree devicetree, but this feature has since been used for boards that
> +  don't
> +- `CONFIG_OF_PRIOR_STAGE` was added in bcm_patch_ as part of a larger Broadcom
> +  change with a tag indicating it only affected one board, so the change in
> +  behaviour was not noticed at the time. It has since been used by RISC-V qemu
> +  boards.
> +
> +Once this bug is fixed, CONFIG_OF_BOARD and CONFIG_OF_PRIOR_STAGE will override
> +(at runtime) the devicetree suppled with U-Boot, but will otherwise use
> +CONFIG_OF_SEPARATE for the in-tree build. So these two will become options,
> +moving out of the 'choice' in `dts/Kconfig`
> +
> +Offending boards are:
> +
> +- bcm7260
> +- bcm7445
> +- qemu_arm64
> +- qemu_arm
> +- qemu-ppce500
> +- qemu-riscv32
> +- qemu-riscv32_smode
> +- qemu-riscv64
> +- qemu-riscv64_smode
> +
> +All of these need to have a devicetree added in-tree. This is targeted to be
> +fixed in the 2022.01 release.
> +
> +
> +Building the devicetree
> +-----------------------
> +
> +U-Boot automatically builds the devicetree for a board, from the
> +`arch/<arch>/dts` directory. The Makefile in those directories has rules for
> +building devicetree files. It is preferable to avoid target-specific rules in
> +those files: i.e. all boards for a particular SoC should be built at once,
> +where practical. Apart from simplifying the Makefile, this helps to efficiently
> +(and immediately) ensure that changes in one board's DT do not break others that
> +are related. Building devicetrees is fast, so performance is seldom a concern
> +here.
> +
> +
> +Overriding the default devicetree
> +---------------------------------
> +
> +When building U-Boot, the `DEVICE_TREE` environment variable allows the
> +default devicetree file to be overridden at build time. This can be useful if
> +modifications have to be made to the in-tree devicetree file, for the benefit
> +of a downstream build system. Note that the in-tree devicetree must be
> +sufficient to build and boot, so this is not a way to bypass that requirement.
> +
> +
> +Modifying the devicetree after building
> +---------------------------------------
> +
> +While it is generally painful and hacky to modify the code or rodata of a
> +program after it is built, in many cases it is useul to do so, e.g. to add

nit: useful

> +configuration information like serial numbers, enabling/disabling features, etc.
> +
> +Devicetree provides a very nice solution to these problems since it is
> +structured data and it is relatively easy to change it, even in binary form
> +(see fdtput).
> +
> +U-Boot takes care that the devicetree is easily accessible after the build
> +process. In fact it is placed in a separate file called `u-boot.dtb`. If the
> +build system wants to modify or replace that file, it can do so. Then all that
> +is needed is to run `binman update` to update the file inside the image. If
> +binman is not used, then `u-boot-nodtb.bin` and the new `u-boot.dtb` can simply
> +be concatenated to achieve the desired result. U-Boot happily copes with the
> +devicetree growing or shrinking.
> +
> +The `u-boot.bin` image contains both pieces. While it is possible to locate the
> +devicetree within the image using the signature at the start of the file, this
> +is a bit messy.
> +
> +This is why `CONFIG_OF_SEPARATE` should always be used when building U-Boot.
> +The `CONFIG_OF_EMBED` option embeds the devicetree somewhere in the U-Boot ELF
> +image as rodata, meaning that it is hard to find it and it cannot increase in
> +size.
> +
> +When modifying the devicetree, the different cases to consider are as follows:
> +
> +- CONFIG_OF_SEPARATE
> +    This is easy, described above. Just change, replace or rebuild the
> +    devicetree so it suits your needs, then rerun binman or redo the `cat`
> +    operation to join `u-boot-nodtb.bin` and the new `u-boot.dtb`
> +
> +- CONFIG_OF_EMBD
> +    This is tricky, since the devicetree cannot easily be located. If the EFL
> +    file is available, then the _dtb_dt_begin and __dtb_dt_end symbols can be
> +    examined to find it. While it is possible to contract the file, it is not
> +    possible to expand the file since that would involve re-linking
> +
> +- CONFIG_OF_PRIOR_STAGE
> +    In this case the devicetree must be modified in the project which provides
> +    it, as described below
> +
> +- CONFIG_OF_BOARD
> +    This is a board-specific situation, so needs to be considered on a
> +    case-by-case base. The devicetree must be modified so that the correct
> +    one is provided to U-Boot. How this is done depends entirely on the
> +    implementation of this option for the board. It might require injecting the
> +    changes into a different project somehow using tooling available there, or
> +    it might involve merging an overlay file at runtime to obtain the desired
> +    result.
> +
> +
> +Devicetree in another project
> +-----------------------------
> +
> +In some cases U-Boot receive its devicetree at runtime from a program that calls
> +it. For example ARM's Trusted Firmware A (`TF-A`_) may have a devicetree that it
> +passes to U-Boot. This overrides any devicetree build by U-Boot. When packaging
> +the firmware, the U-Boot devicetree may in fact be left out if it can be
> +guaranteed that it will receive one from another project.
> +
> +In this case, the devicetree in the other project must track U-Boot's use of
> +device tree. It must provide a way to add configuration and other information to
> +the devicetree for use by U-Boot, such as the /config node. Note that the
> +U-Boot in-tree devicetree must be sufficient to build and boot, so this is not a
> +way to bypass that requirement.
> +
> +If binman is used, the in-tree U-Boot devicetree must contain the binman
> +definition so that a valid image can be build.
> +
> +If verified boot is used, the project must provide a way to inject a public key,
> +certificate or other material into the U-Boot devicetree so that it is available
> +to U-Boot at runtime. See `Signing with U-Boot devicetree`_. This may be
> +through tooling in the project itself or by making use of U-Boot's tooling.
> +
> +
> +Devicetree generated on-the-fly in another project
> +--------------------------------------------------
> +
> +In some rare cases, another project may wish to create a devicetree for U-Boot
> +entirely on-the-fly, then pass it to U-Boot at runtime. The only known example
> +of this at the time of writing (2021) is qemu, for ARM (`QEMU ARM`_) and
> +RISC-V (`QEMU RISC-V`_).
> +
> +In this case, the devicetree in the other project must track U-Boot's use of
> +device tree, so that it remains compatible. If a particular version of the
> +project is needed for a particular version of U-Boot, that must be documented
> +in both projects.
> +
> +Further, it must provide a way to add configuration and other information to
> +the devicetree for use by U-Boot, such as the `/config` node. Note that the
> +U-Boot in-tree devicetree must be sufficient to build and boot, so this is not a
> +way to bypass that requirement.
> +
> +More specifically, tooling or command-line arguments must provide a way to
> +add a `/config` node or items within that node, so that U-Boot can receive a
> +suitable configuration. These options can then be used as part of the build
> +process, which puts the firmware image together. For binman, a way must be
> +provided to add the binman definition into the devicetree in the same way.

Can you elaborate on the purpose here? What sort of things go into
/config which can't be set at compile-time?

> +
> +One way to do this is to allow a .dtsi file to be merged in with the generated
> +devicetree.
> +
> +
> +Passing the devicetree through to Linux
> +---------------------------------------
> +
> +Ideally U-Boot and Linux use the same devicetree source, even though it is
> +hosted in separate projects. U-Boot adds some extra pieces, such as the
> +`config/` node and tags like `u-boot,dm-spl`. Linux adds some extra pieces, such
> +as `linux,default-trigger` and `linux,code`. This should not interfere with
> +each other.
> +
> +In principle it is possible for U-Boot's control devicetree to be passed to
> +Linux. This is, after all, one of the goals of devicetree and the original
> +Open Firmware project, to have the firmware provide the hardware description to
> +the Operating System.
> +
> +For boards where this approach is used, care must be taken. U-Boot typically
> +needs to 'fix up' the devicetree before passing it to Linux, e.g. to add
> +information about the memory map, about which serial console is used, provide
> +the root hash for dm-verify or select whether the console should be silenced for

nit: dm-verity

Is the property for this documented anywhere? A quick grep doesn't find
it in Linux.

> +a faster boot.
> +
> +Fix-ups involve modifying the devicetree. If the control devicetree is used,
> +that means the control devicetree could be modified, while U-Boot is using it.
> +Removing a device and reinserting it can cause problems if the devicetree offset
> +has changed, for example, since the device will be unable to locates its
> +devicetree properties at the expected devicetree offset, which is a fixed
> +integer.
> +
> +To deal with this, it is recommended to employ one or more of the following
> +approaches:
> +
> +- Make a copy of the devicetree and 'fix up' the copy, leaving the control
> +  devicetree alone
> +- Enable `CONFIG_OF_LIVE` so that U-Boot makes its own copy of the devicetree
> +  during relocation; fixups then happen on the original flat tree
> +- Ensure that fix-ups happen after all loading has happened and U-Boot has
> +  completed image verification
> +
> +In practice,the last point is typically observed, since boot_prep_linux() is
> +called just before jumping to Linux, long after signature verification, for
> +example. But it is important to make sure that this line is not blurred,
> +particularly if untrusted user data in involved.

nit: is

> +
> +
> +Devicetree use cases that must be supported
> +-------------------------------------------
> +
> +Regardless of how the devicetree is provided to U-Boot at runtime, various
> +U-Boot features must be fully supported. This section describes some of these
> +features and the implications for other projects.
> +
> +If U-Boot uses its own in-tree devicetree these features are supported
> +automatically.
> +
> +
> +Signing with U-Boot devicetree
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +U-Boot supports signing a payload so that it can be verified to have been
> +created by a party owning a private key. This is called verified boot in U-Boot
> +(see doc/uImage.FIT/verified-boot.txt).
> +
> +Typically this works by creating a FIT and then running the `mkimage` tool to
> +add signatures for particular images. As part of this process, `mkimage` writes
> +a public key to the U-Boot devicetree, although this can be done separately.

It would be nice to just allow adding a public key to a device tree
without signing anything. ATM I have a "dummy" devicetree that I sign
just to add the public key.

> +As with all configuration information, if another project is providing the
> +devicetree to U-Boot, it must provide a way to add this public key into the
> +devicetree it passes to U-Boot. This could be via a tooling option, making use
> +of `mkimage`, or alowing a .dtsi file to be merged in with what is generated in
> +the other project.
> +
> +
> +Providing the binman image definition
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +In complex systems U-Boot must locate and make use of other firmware components,
> +such as images for the user interface, files containing peripheral firmware,
> +multiple copies of U-Boot for use with A/B boot, etc. U-Boot uses
> +:doc:`Binman <binman>` as a standard way of putting an image together.
> +
> +Typically this works by running binman with the devicetree as an input, to
> +create the file image. Binman then outputs an updated devicetree which is
> +packed in the firmware image, so U-Boot can access the binman definition and
> +locate all the components.
> +
> +As with all configuration information, if another project is providing the
> +devicetree to U-Boot, it must provide a way to add this binman definition into
> +the devicetree it passes to U-Boot. This could be via a tooling option, making
> +use of `binman`, or alowing a .dtsi file to be merged in with what is generated

nit: allowing

--Sean

> +in the other project.
> +
> +
> +Protecting the devicetree
> +-------------------------
> +
> +U-Boot relies heavily on devicetree for correct operation. A corrupt or invalid
> +device can cause U-Boot to fail to start, behave incorrectly, crash (e.g. if
> +`CONFIG_OF_LIBFDT_ASSUME_MASK` is adjusted, or fail to boot an Operating System.
> +Within U-Boot, the devicetree is as important as any other part of the source
> +code. At ruuntime, the devicetree can be considered to be structured rodata.
> +
> +With secure systems, care must be taken that the devicetree is valid:
> +
> +- If the code / rodata has a hash or signature, the devicetree should also, if
> +  they are packaged separately.
> +- If the code / rodata is write-protected when running, the devicetree should be
> +  also. Note that U-Boot relocates its code and devicetree, so this is not as
> +  simple as it sounds. U-Boot must write-protect these items after relocating.
> +
> +
> +.. _rpi_patch: https://patchwork.ozlabs.org/project/uboot/patch/20170402082520.32546-1-deymo@google.com/
> +.. _bcm_patch: https://patchwork.ozlabs.org/project/uboot/patch/16fc0901f4521d3c399eac950c52a634b2f9473b.1528485916.git.fitzsim@fitzsim.org/
> +.. _`TF-A`: https://www.trustedfirmware.org/projects/tf-a
> +.. _`QEMU ARM`: https://github.com/qemu/qemu/blob/master/hw/arm/virt.c
> +.. _`QEMU RISC-V`: https://github.com/qemu/qemu/blob/master/hw/riscv/virt.c
> diff --git a/doc/develop/package/index.rst b/doc/develop/package/index.rst
> index 9374be2e62c..188c376950e 100644
> --- a/doc/develop/package/index.rst
> +++ b/doc/develop/package/index.rst
> @@ -17,3 +17,4 @@ SPI flash.
>      :maxdepth: 2
>   
>      binman
> +   devicetree
> 

Re: [PATCH] doc: Add documentation about devicetree usage

[Mark Kettenis]

> From: Simon Glass <sjg@chromium.org>
> Date: Fri, 27 Aug 2021 21:23:48 -0600
> 
> At present some of the ideas and techniques behind devicetree in U-Boot
> are assumed, implied or unsaid. Add some documentation to cover how
> devicetree is build, how it can be modified and the rules about using
> the various CONFIG_OF_... options.
> 
> Signed-off-by: Simon Glass <sjg@chromium.org>
> ---
> 
>  doc/develop/index.rst              |   1 +
>  doc/develop/package/devicetree.rst | 315 +++++++++++++++++++++++++++++
>  doc/develop/package/index.rst      |   1 +
>  3 files changed, 317 insertions(+)
>  create mode 100644 doc/develop/package/devicetree.rst
> 
> diff --git a/doc/develop/index.rst b/doc/develop/index.rst
> index 83c929babda..d5ad8f9fe53 100644
> --- a/doc/develop/index.rst
> +++ b/doc/develop/index.rst
> @@ -36,6 +36,7 @@ Packaging
>     :maxdepth: 1
>  
>     package/index
> +   package/devicetree
>  
>  Testing
>  -------
> diff --git a/doc/develop/package/devicetree.rst b/doc/develop/package/devicetree.rst
> new file mode 100644
> index 00000000000..fccbb182f3e
> --- /dev/null
> +++ b/doc/develop/package/devicetree.rst
> @@ -0,0 +1,315 @@
> +.. SPDX-License-Identifier: GPL-2.0+
> +
> +Updating the devicetree
> +=======================
> +
> +U-Boot uses devicetree for runtime configuration and storing required blobs or
> +any other information it needs to operate. It is possible to update the
> +devicetree separately from actually building U-Boot. This provides a good degree
> +of control and flexibility for firmware that uses U-Boot in conjunction with
> +other project.
> +
> +There are many reasons why it is useful to modify the devicetree after building
> +it:
> +
> +- Configuration can be changed, e.g. which UART to use
> +- A serial number can be added
> +- Public keys can be added to allow image verification
> +- Console output can be changed (e.g. to select serial or vidconsole)
> +
> +This section describes how to work with devicetree to accomplish your goals.
> +
> +See also :doc:`../devicetree/control` for a basic summary of the available
> +features.
> +
> +
> +Devicetree source
> +-----------------
> +
> +Every board in U-Boot must include a devicetree sufficient to build and boot
> +that board on suitable hardware (or emulation). This is specified using the
> +`CONFIG DEFAULT_DEVICE_TREE` option.
> +
> +
> +Current situation (August 2021)
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +As an aside, at present U-Boot allows `CONFIG_DEFAULT_DEVICE_TREE` to be empty,
> +e.g. if `CONFIG_OF_BOARD` or `CONFIG_OF_PRIOR_STAGE` are used. This has
> +unfortunately created an enormous amount of confusion and some wasted effort.
> +This was not intended and this bug will be fixed soon. Specifically:
> +
> +- `CONFIG_OF_BOARD` was added in rpi_patch_ for Raspberry Pi, which does have
> +  an in-tree devicetree, but this feature has since been used for boards that
> +  don't
> +- `CONFIG_OF_PRIOR_STAGE` was added in bcm_patch_ as part of a larger Broadcom
> +  change with a tag indicating it only affected one board, so the change in
> +  behaviour was not noticed at the time. It has since been used by RISC-V qemu
> +  boards.
> +
> +Once this bug is fixed, CONFIG_OF_BOARD and CONFIG_OF_PRIOR_STAGE will override
> +(at runtime) the devicetree suppled with U-Boot, but will otherwise use
> +CONFIG_OF_SEPARATE for the in-tree build. So these two will become options,
> +moving out of the 'choice' in `dts/Kconfig`

Not entirely sure what you mean by this, but for the Raspberry Pi this
should remain a configure option.  For OpenBSD we deliberately opt to
use the device tree provided by the Raspberry Pi firmware because of
the DT overlays.

> +
> +Offending boards are:
> +
> +- bcm7260
> +- bcm7445
> +- qemu_arm64
> +- qemu_arm
> +- qemu-ppce500
> +- qemu-riscv32
> +- qemu-riscv32_smode
> +- qemu-riscv64
> +- qemu-riscv64_smode
> +
> +All of these need to have a devicetree added in-tree. This is targeted to be
> +fixed in the 2022.01 release.

The Linux kernel doesn't seem to have such a requirement and doesn't
provide any device trees for QEMU.  So we can't just copy a device
tree from there and one has to be invented.  IMHO this requirement
makes zero technical sense.

> +Building the devicetree
> +-----------------------
> +
> +U-Boot automatically builds the devicetree for a board, from the
> +`arch/<arch>/dts` directory. The Makefile in those directories has rules for
> +building devicetree files. It is preferable to avoid target-specific rules in
> +those files: i.e. all boards for a particular SoC should be built at once,
> +where practical. Apart from simplifying the Makefile, this helps to efficiently
> +(and immediately) ensure that changes in one board's DT do not break others that
> +are related. Building devicetrees is fast, so performance is seldom a concern
> +here.
> +
> +
> +Overriding the default devicetree
> +---------------------------------
> +
> +When building U-Boot, the `DEVICE_TREE` environment variable allows the
> +default devicetree file to be overridden at build time. This can be useful if
> +modifications have to be made to the in-tree devicetree file, for the benefit
> +of a downstream build system. Note that the in-tree devicetree must be
> +sufficient to build and boot, so this is not a way to bypass that requirement.
> +
> +
> +Modifying the devicetree after building
> +---------------------------------------
> +
> +While it is generally painful and hacky to modify the code or rodata of a
> +program after it is built, in many cases it is useul to do so, e.g. to add
> +configuration information like serial numbers, enabling/disabling features, etc.
> +
> +Devicetree provides a very nice solution to these problems since it is
> +structured data and it is relatively easy to change it, even in binary form
> +(see fdtput).
> +
> +U-Boot takes care that the devicetree is easily accessible after the build
> +process. In fact it is placed in a separate file called `u-boot.dtb`. If the
> +build system wants to modify or replace that file, it can do so. Then all that
> +is needed is to run `binman update` to update the file inside the image. If
> +binman is not used, then `u-boot-nodtb.bin` and the new `u-boot.dtb` can simply
> +be concatenated to achieve the desired result. U-Boot happily copes with the
> +devicetree growing or shrinking.
> +
> +The `u-boot.bin` image contains both pieces. While it is possible to locate the
> +devicetree within the image using the signature at the start of the file, this
> +is a bit messy.
> +
> +This is why `CONFIG_OF_SEPARATE` should always be used when building U-Boot.
> +The `CONFIG_OF_EMBED` option embeds the devicetree somewhere in the U-Boot ELF
> +image as rodata, meaning that it is hard to find it and it cannot increase in
> +size.
> +
> +When modifying the devicetree, the different cases to consider are as follows:
> +
> +- CONFIG_OF_SEPARATE
> +    This is easy, described above. Just change, replace or rebuild the
> +    devicetree so it suits your needs, then rerun binman or redo the `cat`
> +    operation to join `u-boot-nodtb.bin` and the new `u-boot.dtb`
> +
> +- CONFIG_OF_EMBD
> +    This is tricky, since the devicetree cannot easily be located. If the EFL
> +    file is available, then the _dtb_dt_begin and __dtb_dt_end symbols can be
> +    examined to find it. While it is possible to contract the file, it is not
> +    possible to expand the file since that would involve re-linking
> +
> +- CONFIG_OF_PRIOR_STAGE
> +    In this case the devicetree must be modified in the project which provides
> +    it, as described below
> +
> +- CONFIG_OF_BOARD
> +    This is a board-specific situation, so needs to be considered on a
> +    case-by-case base. The devicetree must be modified so that the correct
> +    one is provided to U-Boot. How this is done depends entirely on the
> +    implementation of this option for the board. It might require injecting the
> +    changes into a different project somehow using tooling available there, or
> +    it might involve merging an overlay file at runtime to obtain the desired
> +    result.
> +
> +
> +Devicetree in another project
> +-----------------------------
> +
> +In some cases U-Boot receive its devicetree at runtime from a program that calls
> +it. For example ARM's Trusted Firmware A (`TF-A`_) may have a devicetree that it
> +passes to U-Boot. This overrides any devicetree build by U-Boot. When packaging
> +the firmware, the U-Boot devicetree may in fact be left out if it can be
> +guaranteed that it will receive one from another project.
> +
> +In this case, the devicetree in the other project must track U-Boot's use of
> +device tree. It must provide a way to add configuration and other information to
> +the devicetree for use by U-Boot, such as the /config node. Note that the
> +U-Boot in-tree devicetree must be sufficient to build and boot, so this is not a
> +way to bypass that requirement.
> +
> +If binman is used, the in-tree U-Boot devicetree must contain the binman
> +definition so that a valid image can be build.
> +
> +If verified boot is used, the project must provide a way to inject a public key,
> +certificate or other material into the U-Boot devicetree so that it is available
> +to U-Boot at runtime. See `Signing with U-Boot devicetree`_. This may be
> +through tooling in the project itself or by making use of U-Boot's tooling.
> +
> +
> +Devicetree generated on-the-fly in another project
> +--------------------------------------------------
> +
> +In some rare cases, another project may wish to create a devicetree for U-Boot
> +entirely on-the-fly, then pass it to U-Boot at runtime. The only known example
> +of this at the time of writing (2021) is qemu, for ARM (`QEMU ARM`_) and
> +RISC-V (`QEMU RISC-V`_).
> +
> +In this case, the devicetree in the other project must track U-Boot's use of
> +device tree, so that it remains compatible. If a particular version of the
> +project is needed for a particular version of U-Boot, that must be documented
> +in both projects.
> +
> +Further, it must provide a way to add configuration and other information to
> +the devicetree for use by U-Boot, such as the `/config` node. Note that the
> +U-Boot in-tree devicetree must be sufficient to build and boot, so this is not a
> +way to bypass that requirement.
> +
> +More specifically, tooling or command-line arguments must provide a way to
> +add a `/config` node or items within that node, so that U-Boot can receive a
> +suitable configuration. These options can then be used as part of the build
> +process, which puts the firmware image together. For binman, a way must be
> +provided to add the binman definition into the devicetree in the same way.
> +
> +One way to do this is to allow a .dtsi file to be merged in with the generated
> +devicetree.
> +
> +
> +Passing the devicetree through to Linux
> +---------------------------------------
> +
> +Ideally U-Boot and Linux use the same devicetree source, even though it is
> +hosted in separate projects. U-Boot adds some extra pieces, such as the
> +`config/` node and tags like `u-boot,dm-spl`. Linux adds some extra pieces, such
> +as `linux,default-trigger` and `linux,code`. This should not interfere with
> +each other.
> +
> +In principle it is possible for U-Boot's control devicetree to be passed to
> +Linux. This is, after all, one of the goals of devicetree and the original
> +Open Firmware project, to have the firmware provide the hardware description to
> +the Operating System.
> +
> +For boards where this approach is used, care must be taken. U-Boot typically
> +needs to 'fix up' the devicetree before passing it to Linux, e.g. to add
> +information about the memory map, about which serial console is used, provide
> +the root hash for dm-verify or select whether the console should be silenced for
> +a faster boot.
> +
> +Fix-ups involve modifying the devicetree. If the control devicetree is used,
> +that means the control devicetree could be modified, while U-Boot is using it.
> +Removing a device and reinserting it can cause problems if the devicetree offset
> +has changed, for example, since the device will be unable to locates its
> +devicetree properties at the expected devicetree offset, which is a fixed
> +integer.
> +
> +To deal with this, it is recommended to employ one or more of the following
> +approaches:
> +
> +- Make a copy of the devicetree and 'fix up' the copy, leaving the control
> +  devicetree alone
> +- Enable `CONFIG_OF_LIVE` so that U-Boot makes its own copy of the devicetree
> +  during relocation; fixups then happen on the original flat tree
> +- Ensure that fix-ups happen after all loading has happened and U-Boot has
> +  completed image verification
> +
> +In practice,the last point is typically observed, since boot_prep_linux() is
> +called just before jumping to Linux, long after signature verification, for
> +example. But it is important to make sure that this line is not blurred,
> +particularly if untrusted user data in involved.
> +
> +
> +Devicetree use cases that must be supported
> +-------------------------------------------
> +
> +Regardless of how the devicetree is provided to U-Boot at runtime, various
> +U-Boot features must be fully supported. This section describes some of these
> +features and the implications for other projects.
> +
> +If U-Boot uses its own in-tree devicetree these features are supported
> +automatically.
> +
> +
> +Signing with U-Boot devicetree
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +U-Boot supports signing a payload so that it can be verified to have been
> +created by a party owning a private key. This is called verified boot in U-Boot
> +(see doc/uImage.FIT/verified-boot.txt).
> +
> +Typically this works by creating a FIT and then running the `mkimage` tool to
> +add signatures for particular images. As part of this process, `mkimage` writes
> +a public key to the U-Boot devicetree, although this can be done separately.
> +
> +As with all configuration information, if another project is providing the
> +devicetree to U-Boot, it must provide a way to add this public key into the
> +devicetree it passes to U-Boot. This could be via a tooling option, making use
> +of `mkimage`, or alowing a .dtsi file to be merged in with what is generated in
> +the other project.
> +
> +
> +Providing the binman image definition
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +In complex systems U-Boot must locate and make use of other firmware components,
> +such as images for the user interface, files containing peripheral firmware,
> +multiple copies of U-Boot for use with A/B boot, etc. U-Boot uses
> +:doc:`Binman <binman>` as a standard way of putting an image together.
> +
> +Typically this works by running binman with the devicetree as an input, to
> +create the file image. Binman then outputs an updated devicetree which is
> +packed in the firmware image, so U-Boot can access the binman definition and
> +locate all the components.
> +
> +As with all configuration information, if another project is providing the
> +devicetree to U-Boot, it must provide a way to add this binman definition into
> +the devicetree it passes to U-Boot. This could be via a tooling option, making
> +use of `binman`, or alowing a .dtsi file to be merged in with what is generated
> +in the other project.
> +
> +
> +Protecting the devicetree
> +-------------------------
> +
> +U-Boot relies heavily on devicetree for correct operation. A corrupt or invalid
> +device can cause U-Boot to fail to start, behave incorrectly, crash (e.g. if
> +`CONFIG_OF_LIBFDT_ASSUME_MASK` is adjusted, or fail to boot an Operating System.
> +Within U-Boot, the devicetree is as important as any other part of the source
> +code. At ruuntime, the devicetree can be considered to be structured rodata.
> +
> +With secure systems, care must be taken that the devicetree is valid:
> +
> +- If the code / rodata has a hash or signature, the devicetree should also, if
> +  they are packaged separately.
> +- If the code / rodata is write-protected when running, the devicetree should be
> +  also. Note that U-Boot relocates its code and devicetree, so this is not as
> +  simple as it sounds. U-Boot must write-protect these items after relocating.
> +
> +
> +.. _rpi_patch: https://patchwork.ozlabs.org/project/uboot/patch/20170402082520.32546-1-deymo@google.com/
> +.. _bcm_patch: https://patchwork.ozlabs.org/project/uboot/patch/16fc0901f4521d3c399eac950c52a634b2f9473b.1528485916.git.fitzsim@fitzsim.org/
> +.. _`TF-A`: https://www.trustedfirmware.org/projects/tf-a
> +.. _`QEMU ARM`: https://github.com/qemu/qemu/blob/master/hw/arm/virt.c
> +.. _`QEMU RISC-V`: https://github.com/qemu/qemu/blob/master/hw/riscv/virt.c
> diff --git a/doc/develop/package/index.rst b/doc/develop/package/index.rst
> index 9374be2e62c..188c376950e 100644
> --- a/doc/develop/package/index.rst
> +++ b/doc/develop/package/index.rst
> @@ -17,3 +17,4 @@ SPI flash.
>     :maxdepth: 2
>  
>     binman
> +   devicetree
> -- 
> 2.33.0.259.gc128427fd7-goog
> 
> 

Re: [PATCH] doc: Add documentation about devicetree usage

[Heinrich Schuchardt]

On 8/28/21 5:23 AM, Simon Glass wrote:
> At present some of the ideas and techniques behind devicetree in U-Boot
> are assumed, implied or unsaid. Add some documentation to cover how
> devicetree is build, how it can be modified and the rules about using
> the various CONFIG_OF_... options.
>
> Signed-off-by: Simon Glass <sjg@chromium.org>
> ---
>
>   doc/develop/index.rst              |   1 +
>   doc/develop/package/devicetree.rst | 315 +++++++++++++++++++++++++++++
>   doc/develop/package/index.rst      |   1 +
>   3 files changed, 317 insertions(+)
>   create mode 100644 doc/develop/package/devicetree.rst
>
> diff --git a/doc/develop/index.rst b/doc/develop/index.rst
> index 83c929babda..d5ad8f9fe53 100644
> --- a/doc/develop/index.rst
> +++ b/doc/develop/index.rst
> @@ -36,6 +36,7 @@ Packaging
>      :maxdepth: 1
>
>      package/index
> +   package/devicetree
>
>   Testing
>   -------
> diff --git a/doc/develop/package/devicetree.rst b/doc/develop/package/devicetree.rst
> new file mode 100644
> index 00000000000..fccbb182f3e
> --- /dev/null
> +++ b/doc/develop/package/devicetree.rst
> @@ -0,0 +1,315 @@
> +.. SPDX-License-Identifier: GPL-2.0+
> +
> +Updating the devicetree
> +=======================
> +
> +U-Boot uses devicetree for runtime configuration and storing required blobs or
> +any other information it needs to operate. It is possible to update the
> +devicetree separately from actually building U-Boot. This provides a good degree
> +of control and flexibility for firmware that uses U-Boot in conjunction with
> +other project.
> +
> +There are many reasons why it is useful to modify the devicetree after building
> +it:
> +
> +- Configuration can be changed, e.g. which UART to use
> +- A serial number can be added
> +- Public keys can be added to allow image verification
> +- Console output can be changed (e.g. to select serial or vidconsole)
> +
> +This section describes how to work with devicetree to accomplish your goals.
> +
> +See also :doc:`../devicetree/control` for a basic summary of the available
> +features.
> +
> +
> +Devicetree source
> +-----------------
> +
> +Every board in U-Boot must include a devicetree sufficient to build and boot
> +that board on suitable hardware (or emulation). This is specified using the
> +`CONFIG DEFAULT_DEVICE_TREE` option.
> +
> +
> +Current situation (August 2021)
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +As an aside, at present U-Boot allows `CONFIG_DEFAULT_DEVICE_TREE` to be empty,
> +e.g. if `CONFIG_OF_BOARD` or `CONFIG_OF_PRIOR_STAGE` are used. This has
> +unfortunately created an enormous amount of confusion and some wasted effort.
> +This was not intended and this bug will be fixed soon. Specifically:
> +
> +- `CONFIG_OF_BOARD` was added in rpi_patch_ for Raspberry Pi, which does have
> +  an in-tree devicetree, but this feature has since been used for boards that
> +  don't
> +- `CONFIG_OF_PRIOR_STAGE` was added in bcm_patch_ as part of a larger Broadcom
> +  change with a tag indicating it only affected one board, so the change in
> +  behaviour was not noticed at the time. It has since been used by RISC-V qemu
> +  boards.
> +
> +Once this bug is fixed, CONFIG_OF_BOARD and CONFIG_OF_PRIOR_STAGE will override
> +(at runtime) the devicetree suppled with U-Boot, but will otherwise use
> +CONFIG_OF_SEPARATE for the in-tree build. So these two will become options,
> +moving out of the 'choice' in `dts/Kconfig`
> +
> +Offending boards are:
> +
> +- bcm7260
> +- bcm7445
> +- qemu_arm64
> +- qemu_arm
> +- qemu-ppce500
> +- qemu-riscv32
> +- qemu-riscv32_smode
> +- qemu-riscv64
> +- qemu-riscv64_smode
> +
> +All of these need to have a devicetree added in-tree. This is targeted to be
> +fixed in the 2022.01 release.
> +
> +
> +Building the devicetree
> +-----------------------
> +
> +U-Boot automatically builds the devicetree for a board, from the
> +`arch/<arch>/dts` directory. The Makefile in those directories has rules for
> +building devicetree files. It is preferable to avoid target-specific rules in
> +those files: i.e. all boards for a particular SoC should be built at once,
> +where practical. Apart from simplifying the Makefile, this helps to efficiently
> +(and immediately) ensure that changes in one board's DT do not break others that
> +are related. Building devicetrees is fast, so performance is seldom a concern
> +here.
> +
> +
> +Overriding the default devicetree
> +---------------------------------
> +
> +When building U-Boot, the `DEVICE_TREE` environment variable allows the
> +default devicetree file to be overridden at build time. This can be useful if
> +modifications have to be made to the in-tree devicetree file, for the benefit
> +of a downstream build system. Note that the in-tree devicetree must be
> +sufficient to build and boot, so this is not a way to bypass that requirement.
> +
> +
> +Modifying the devicetree after building
> +---------------------------------------
> +
> +While it is generally painful and hacky to modify the code or rodata of a
> +program after it is built, in many cases it is useul to do so, e.g. to add
> +configuration information like serial numbers, enabling/disabling features, etc.
> +
> +Devicetree provides a very nice solution to these problems since it is
> +structured data and it is relatively easy to change it, even in binary form
> +(see fdtput).
> +
> +U-Boot takes care that the devicetree is easily accessible after the build
> +process. In fact it is placed in a separate file called `u-boot.dtb`. If the
> +build system wants to modify or replace that file, it can do so. Then all that
> +is needed is to run `binman update` to update the file inside the image. If
> +binman is not used, then `u-boot-nodtb.bin` and the new `u-boot.dtb` can simply
> +be concatenated to achieve the desired result. U-Boot happily copes with the
> +devicetree growing or shrinking.
> +
> +The `u-boot.bin` image contains both pieces. While it is possible to locate the
> +devicetree within the image using the signature at the start of the file, this
> +is a bit messy.
> +
> +This is why `CONFIG_OF_SEPARATE` should always be used when building U-Boot.
> +The `CONFIG_OF_EMBED` option embeds the devicetree somewhere in the U-Boot ELF
> +image as rodata, meaning that it is hard to find it and it cannot increase in
> +size.
> +
> +When modifying the devicetree, the different cases to consider are as follows:
> +
> +- CONFIG_OF_SEPARATE
> +    This is easy, described above. Just change, replace or rebuild the
> +    devicetree so it suits your needs, then rerun binman or redo the `cat`
> +    operation to join `u-boot-nodtb.bin` and the new `u-boot.dtb`
> +
> +- CONFIG_OF_EMBD
> +    This is tricky, since the devicetree cannot easily be located. If the EFL
> +    file is available, then the _dtb_dt_begin and __dtb_dt_end symbols can be
> +    examined to find it. While it is possible to contract the file, it is not
> +    possible to expand the file since that would involve re-linking
> +
> +- CONFIG_OF_PRIOR_STAGE
> +    In this case the devicetree must be modified in the project which provides
> +    it, as described below
> +
> +- CONFIG_OF_BOARD
> +    This is a board-specific situation, so needs to be considered on a
> +    case-by-case base. The devicetree must be modified so that the correct
> +    one is provided to U-Boot. How this is done depends entirely on the
> +    implementation of this option for the board. It might require injecting the
> +    changes into a different project somehow using tooling available there, or
> +    it might involve merging an overlay file at runtime to obtain the desired
> +    result.
> +
> +
> +Devicetree in another project
> +-----------------------------
> +
> +In some cases U-Boot receive its devicetree at runtime from a program that calls
> +it. For example ARM's Trusted Firmware A (`TF-A`_) may have a devicetree that it
> +passes to U-Boot. This overrides any devicetree build by U-Boot. When packaging
> +the firmware, the U-Boot devicetree may in fact be left out if it can be
> +guaranteed that it will receive one from another project.
> +
> +In this case, the devicetree in the other project must track U-Boot's use of
> +device tree. It must provide a way to add configuration and other information to

U-Boot does not rule the world. So never ever is this going to happen.
It is the other way round. U-Boot must consume what the prior bootstage
delivers. If U-Boot needs extra nodes it has to provide these on its own.

Please, remove this assumption from the document.

> +the devicetree for use by U-Boot, such as the /config node. Note that the
> +U-Boot in-tree devicetree must be sufficient to build and boot, so this is not a
> +way to bypass that requirement.
> +
> +If binman is used, the in-tree U-Boot devicetree must contain the binman
> +definition so that a valid image can be build.

No clue what an in-tree tree might be. Please, avoid such confusing
language.

> +
> +If verified boot is used, the project must provide a way to inject a public key,

%s/the project/U-Boot/

> +certificate or other material into the U-Boot devicetree so that it is available
> +to U-Boot at runtime. See `Signing with U-Boot devicetree`_. This may be
> +through tooling in the project itself or by making use of U-Boot's tooling.
> +
> +
> +Devicetree generated on-the-fly in another project
> +--------------------------------------------------
> +
> +In some rare cases, another project may wish to create a devicetree for U-Boot
> +entirely on-the-fly, then pass it to U-Boot at runtime. The only known example
> +of this at the time of writing (2021) is qemu, for ARM (`QEMU ARM`_) and
> +RISC-V (`QEMU RISC-V`_).
> +
> +In this case, the devicetree in the other project must track U-Boot's use of
> +device tree, so that it remains compatible. If a particular version of the

Why? U-Boot must support its internal needs itself!

Don't try to force a bad U-Boot design on other projects.

Please, come up with a concept that makes sense.

Best regards

Heinrich

> +project is needed for a particular version of U-Boot, that must be documented
> +in both projects.
> +
> +Further, it must provide a way to add configuration and other information to
> +the devicetree for use by U-Boot, such as the `/config` node. Note that the
> +U-Boot in-tree devicetree must be sufficient to build and boot, so this is not a
> +way to bypass that requirement.
> +
> +More specifically, tooling or command-line arguments must provide a way to
> +add a `/config` node or items within that node, so that U-Boot can receive a
> +suitable configuration. These options can then be used as part of the build
> +process, which puts the firmware image together. For binman, a way must be
> +provided to add the binman definition into the devicetree in the same way.
> +
> +One way to do this is to allow a .dtsi file to be merged in with the generated
> +devicetree.
> +
> +
> +Passing the devicetree through to Linux
> +---------------------------------------
> +
> +Ideally U-Boot and Linux use the same devicetree source, even though it is
> +hosted in separate projects. U-Boot adds some extra pieces, such as the
> +`config/` node and tags like `u-boot,dm-spl`. Linux adds some extra pieces, such
> +as `linux,default-trigger` and `linux,code`. This should not interfere with
> +each other.
> +
> +In principle it is possible for U-Boot's control devicetree to be passed to
> +Linux. This is, after all, one of the goals of devicetree and the original
> +Open Firmware project, to have the firmware provide the hardware description to
> +the Operating System.
> +
> +For boards where this approach is used, care must be taken. U-Boot typically
> +needs to 'fix up' the devicetree before passing it to Linux, e.g. to add
> +information about the memory map, about which serial console is used, provide
> +the root hash for dm-verify or select whether the console should be silenced for
> +a faster boot.
> +
> +Fix-ups involve modifying the devicetree. If the control devicetree is used,
> +that means the control devicetree could be modified, while U-Boot is using it.
> +Removing a device and reinserting it can cause problems if the devicetree offset
> +has changed, for example, since the device will be unable to locates its
> +devicetree properties at the expected devicetree offset, which is a fixed
> +integer.
> +
> +To deal with this, it is recommended to employ one or more of the following
> +approaches:
> +
> +- Make a copy of the devicetree and 'fix up' the copy, leaving the control
> +  devicetree alone
> +- Enable `CONFIG_OF_LIVE` so that U-Boot makes its own copy of the devicetree
> +  during relocation; fixups then happen on the original flat tree
> +- Ensure that fix-ups happen after all loading has happened and U-Boot has
> +  completed image verification
> +
> +In practice,the last point is typically observed, since boot_prep_linux() is
> +called just before jumping to Linux, long after signature verification, for
> +example. But it is important to make sure that this line is not blurred,
> +particularly if untrusted user data in involved.
> +
> +
> +Devicetree use cases that must be supported
> +-------------------------------------------
> +
> +Regardless of how the devicetree is provided to U-Boot at runtime, various
> +U-Boot features must be fully supported. This section describes some of these
> +features and the implications for other projects.
> +
> +If U-Boot uses its own in-tree devicetree these features are supported
> +automatically.
> +
> +
> +Signing with U-Boot devicetree
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +U-Boot supports signing a payload so that it can be verified to have been
> +created by a party owning a private key. This is called verified boot in U-Boot
> +(see doc/uImage.FIT/verified-boot.txt).
> +
> +Typically this works by creating a FIT and then running the `mkimage` tool to
> +add signatures for particular images. As part of this process, `mkimage` writes
> +a public key to the U-Boot devicetree, although this can be done separately.
> +
> +As with all configuration information, if another project is providing the
> +devicetree to U-Boot, it must provide a way to add this public key into the
> +devicetree it passes to U-Boot. This could be via a tooling option, making use
> +of `mkimage`, or alowing a .dtsi file to be merged in with what is generated in
> +the other project.
> +
> +
> +Providing the binman image definition
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +In complex systems U-Boot must locate and make use of other firmware components,
> +such as images for the user interface, files containing peripheral firmware,
> +multiple copies of U-Boot for use with A/B boot, etc. U-Boot uses
> +:doc:`Binman <binman>` as a standard way of putting an image together.
> +
> +Typically this works by running binman with the devicetree as an input, to
> +create the file image. Binman then outputs an updated devicetree which is
> +packed in the firmware image, so U-Boot can access the binman definition and
> +locate all the components.
> +
> +As with all configuration information, if another project is providing the
> +devicetree to U-Boot, it must provide a way to add this binman definition into
> +the devicetree it passes to U-Boot. This could be via a tooling option, making
> +use of `binman`, or alowing a .dtsi file to be merged in with what is generated
> +in the other project.
> +
> +
> +Protecting the devicetree
> +-------------------------
> +
> +U-Boot relies heavily on devicetree for correct operation. A corrupt or invalid
> +device can cause U-Boot to fail to start, behave incorrectly, crash (e.g. if
> +`CONFIG_OF_LIBFDT_ASSUME_MASK` is adjusted, or fail to boot an Operating System.
> +Within U-Boot, the devicetree is as important as any other part of the source
> +code. At ruuntime, the devicetree can be considered to be structured rodata.
> +
> +With secure systems, care must be taken that the devicetree is valid:
> +
> +- If the code / rodata has a hash or signature, the devicetree should also, if
> +  they are packaged separately.
> +- If the code / rodata is write-protected when running, the devicetree should be
> +  also. Note that U-Boot relocates its code and devicetree, so this is not as
> +  simple as it sounds. U-Boot must write-protect these items after relocating.
> +
> +
> +.. _rpi_patch: https://patchwork.ozlabs.org/project/uboot/patch/20170402082520.32546-1-deymo@google.com/
> +.. _bcm_patch: https://patchwork.ozlabs.org/project/uboot/patch/16fc0901f4521d3c399eac950c52a634b2f9473b.1528485916.git.fitzsim@fitzsim.org/
> +.. _`TF-A`: https://www.trustedfirmware.org/projects/tf-a
> +.. _`QEMU ARM`: https://github.com/qemu/qemu/blob/master/hw/arm/virt.c
> +.. _`QEMU RISC-V`: https://github.com/qemu/qemu/blob/master/hw/riscv/virt.c
> diff --git a/doc/develop/package/index.rst b/doc/develop/package/index.rst
> index 9374be2e62c..188c376950e 100644
> --- a/doc/develop/package/index.rst
> +++ b/doc/develop/package/index.rst
> @@ -17,3 +17,4 @@ SPI flash.
>      :maxdepth: 2
>
>      binman
> +   devicetree
>

Re: [PATCH] doc: Add documentation about devicetree usage

[Tom Rini]

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On Sat, Aug 28, 2021 at 02:29:21PM +0200, Heinrich Schuchardt wrote:
> On 8/28/21 5:23 AM, Simon Glass wrote:
> > At present some of the ideas and techniques behind devicetree in U-Boot
> > are assumed, implied or unsaid. Add some documentation to cover how
> > devicetree is build, how it can be modified and the rules about using
> > the various CONFIG_OF_... options.
> > 
> > Signed-off-by: Simon Glass <sjg@chromium.org>
> > ---
> > 
> >   doc/develop/index.rst              |   1 +
> >   doc/develop/package/devicetree.rst | 315 +++++++++++++++++++++++++++++
> >   doc/develop/package/index.rst      |   1 +
> >   3 files changed, 317 insertions(+)
> >   create mode 100644 doc/develop/package/devicetree.rst
> > 
> > diff --git a/doc/develop/index.rst b/doc/develop/index.rst
> > index 83c929babda..d5ad8f9fe53 100644
> > --- a/doc/develop/index.rst
> > +++ b/doc/develop/index.rst
> > @@ -36,6 +36,7 @@ Packaging
> >      :maxdepth: 1
> > 
> >      package/index
> > +   package/devicetree
> > 
> >   Testing
> >   -------
> > diff --git a/doc/develop/package/devicetree.rst b/doc/develop/package/devicetree.rst
> > new file mode 100644
> > index 00000000000..fccbb182f3e
> > --- /dev/null
> > +++ b/doc/develop/package/devicetree.rst
> > @@ -0,0 +1,315 @@
> > +.. SPDX-License-Identifier: GPL-2.0+
> > +
> > +Updating the devicetree
> > +=======================
> > +
> > +U-Boot uses devicetree for runtime configuration and storing required blobs or
> > +any other information it needs to operate. It is possible to update the
> > +devicetree separately from actually building U-Boot. This provides a good degree
> > +of control and flexibility for firmware that uses U-Boot in conjunction with
> > +other project.
> > +
> > +There are many reasons why it is useful to modify the devicetree after building
> > +it:
> > +
> > +- Configuration can be changed, e.g. which UART to use
> > +- A serial number can be added
> > +- Public keys can be added to allow image verification
> > +- Console output can be changed (e.g. to select serial or vidconsole)
> > +
> > +This section describes how to work with devicetree to accomplish your goals.
> > +
> > +See also :doc:`../devicetree/control` for a basic summary of the available
> > +features.
> > +
> > +
> > +Devicetree source
> > +-----------------
> > +
> > +Every board in U-Boot must include a devicetree sufficient to build and boot
> > +that board on suitable hardware (or emulation). This is specified using the
> > +`CONFIG DEFAULT_DEVICE_TREE` option.
> > +
> > +
> > +Current situation (August 2021)
> > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > +
> > +As an aside, at present U-Boot allows `CONFIG_DEFAULT_DEVICE_TREE` to be empty,
> > +e.g. if `CONFIG_OF_BOARD` or `CONFIG_OF_PRIOR_STAGE` are used. This has
> > +unfortunately created an enormous amount of confusion and some wasted effort.
> > +This was not intended and this bug will be fixed soon. Specifically:
> > +
> > +- `CONFIG_OF_BOARD` was added in rpi_patch_ for Raspberry Pi, which does have
> > +  an in-tree devicetree, but this feature has since been used for boards that
> > +  don't
> > +- `CONFIG_OF_PRIOR_STAGE` was added in bcm_patch_ as part of a larger Broadcom
> > +  change with a tag indicating it only affected one board, so the change in
> > +  behaviour was not noticed at the time. It has since been used by RISC-V qemu
> > +  boards.
> > +
> > +Once this bug is fixed, CONFIG_OF_BOARD and CONFIG_OF_PRIOR_STAGE will override
> > +(at runtime) the devicetree suppled with U-Boot, but will otherwise use
> > +CONFIG_OF_SEPARATE for the in-tree build. So these two will become options,
> > +moving out of the 'choice' in `dts/Kconfig`
> > +
> > +Offending boards are:
> > +
> > +- bcm7260
> > +- bcm7445
> > +- qemu_arm64
> > +- qemu_arm
> > +- qemu-ppce500
> > +- qemu-riscv32
> > +- qemu-riscv32_smode
> > +- qemu-riscv64
> > +- qemu-riscv64_smode
> > +
> > +All of these need to have a devicetree added in-tree. This is targeted to be
> > +fixed in the 2022.01 release.
> > +
> > +
> > +Building the devicetree
> > +-----------------------
> > +
> > +U-Boot automatically builds the devicetree for a board, from the
> > +`arch/<arch>/dts` directory. The Makefile in those directories has rules for
> > +building devicetree files. It is preferable to avoid target-specific rules in
> > +those files: i.e. all boards for a particular SoC should be built at once,
> > +where practical. Apart from simplifying the Makefile, this helps to efficiently
> > +(and immediately) ensure that changes in one board's DT do not break others that
> > +are related. Building devicetrees is fast, so performance is seldom a concern
> > +here.
> > +
> > +
> > +Overriding the default devicetree
> > +---------------------------------
> > +
> > +When building U-Boot, the `DEVICE_TREE` environment variable allows the
> > +default devicetree file to be overridden at build time. This can be useful if
> > +modifications have to be made to the in-tree devicetree file, for the benefit
> > +of a downstream build system. Note that the in-tree devicetree must be
> > +sufficient to build and boot, so this is not a way to bypass that requirement.
> > +
> > +
> > +Modifying the devicetree after building
> > +---------------------------------------
> > +
> > +While it is generally painful and hacky to modify the code or rodata of a
> > +program after it is built, in many cases it is useul to do so, e.g. to add
> > +configuration information like serial numbers, enabling/disabling features, etc.
> > +
> > +Devicetree provides a very nice solution to these problems since it is
> > +structured data and it is relatively easy to change it, even in binary form
> > +(see fdtput).
> > +
> > +U-Boot takes care that the devicetree is easily accessible after the build
> > +process. In fact it is placed in a separate file called `u-boot.dtb`. If the
> > +build system wants to modify or replace that file, it can do so. Then all that
> > +is needed is to run `binman update` to update the file inside the image. If
> > +binman is not used, then `u-boot-nodtb.bin` and the new `u-boot.dtb` can simply
> > +be concatenated to achieve the desired result. U-Boot happily copes with the
> > +devicetree growing or shrinking.
> > +
> > +The `u-boot.bin` image contains both pieces. While it is possible to locate the
> > +devicetree within the image using the signature at the start of the file, this
> > +is a bit messy.
> > +
> > +This is why `CONFIG_OF_SEPARATE` should always be used when building U-Boot.
> > +The `CONFIG_OF_EMBED` option embeds the devicetree somewhere in the U-Boot ELF
> > +image as rodata, meaning that it is hard to find it and it cannot increase in
> > +size.
> > +
> > +When modifying the devicetree, the different cases to consider are as follows:
> > +
> > +- CONFIG_OF_SEPARATE
> > +    This is easy, described above. Just change, replace or rebuild the
> > +    devicetree so it suits your needs, then rerun binman or redo the `cat`
> > +    operation to join `u-boot-nodtb.bin` and the new `u-boot.dtb`
> > +
> > +- CONFIG_OF_EMBD
> > +    This is tricky, since the devicetree cannot easily be located. If the EFL
> > +    file is available, then the _dtb_dt_begin and __dtb_dt_end symbols can be
> > +    examined to find it. While it is possible to contract the file, it is not
> > +    possible to expand the file since that would involve re-linking
> > +
> > +- CONFIG_OF_PRIOR_STAGE
> > +    In this case the devicetree must be modified in the project which provides
> > +    it, as described below
> > +
> > +- CONFIG_OF_BOARD
> > +    This is a board-specific situation, so needs to be considered on a
> > +    case-by-case base. The devicetree must be modified so that the correct
> > +    one is provided to U-Boot. How this is done depends entirely on the
> > +    implementation of this option for the board. It might require injecting the
> > +    changes into a different project somehow using tooling available there, or
> > +    it might involve merging an overlay file at runtime to obtain the desired
> > +    result.
> > +
> > +
> > +Devicetree in another project
> > +-----------------------------
> > +
> > +In some cases U-Boot receive its devicetree at runtime from a program that calls
> > +it. For example ARM's Trusted Firmware A (`TF-A`_) may have a devicetree that it
> > +passes to U-Boot. This overrides any devicetree build by U-Boot. When packaging
> > +the firmware, the U-Boot devicetree may in fact be left out if it can be
> > +guaranteed that it will receive one from another project.
> > +
> > +In this case, the devicetree in the other project must track U-Boot's use of
> > +device tree. It must provide a way to add configuration and other information to
> 
> U-Boot does not rule the world. So never ever is this going to happen.
> It is the other way round. U-Boot must consume what the prior bootstage
> delivers. If U-Boot needs extra nodes it has to provide these on its own.
> 
> Please, remove this assumption from the document.

We need to figure out which compatibles we need to push upstream, and
which we need to see if we can solve another way.

> > +the devicetree for use by U-Boot, such as the /config node. Note that the
> > +U-Boot in-tree devicetree must be sufficient to build and boot, so this is not a
> > +way to bypass that requirement.
> > +
> > +If binman is used, the in-tree U-Boot devicetree must contain the binman
> > +definition so that a valid image can be build.
> 
> No clue what an in-tree tree might be. Please, avoid such confusing
> language.

Would "source tree devicetree" be less confusing?  Or can you suggest an
alternative?

> 
> > +
> > +If verified boot is used, the project must provide a way to inject a public key,
> 
> %s/the project/U-Boot/
> 
> > +certificate or other material into the U-Boot devicetree so that it is available
> > +to U-Boot at runtime. See `Signing with U-Boot devicetree`_. This may be
> > +through tooling in the project itself or by making use of U-Boot's tooling.
> > +
> > +
> > +Devicetree generated on-the-fly in another project
> > +--------------------------------------------------

I think this is a confusing topic, and gets things a bit backwards.

> > +
> > +In some rare cases, another project may wish to create a devicetree for U-Boot
> > +entirely on-the-fly, then pass it to U-Boot at runtime. The only known example
> > +of this at the time of writing (2021) is qemu, for ARM (`QEMU ARM`_) and
> > +RISC-V (`QEMU RISC-V`_).

What's the difference between QEMU and hardware that ships with a device
tree stored in flash?  In both cases, we need to have the device tree
that's provided be the device tree that works.  Like I was just raising
in another thread, there are not multiple device trees for a given
device, there is the device tree and it works for everyone that needs to
consume a device tree.

> > +In this case, the devicetree in the other project must track U-Boot's use of
> > +device tree, so that it remains compatible. If a particular version of the
> 
> Why? U-Boot must support its internal needs itself!
> 
> Don't try to force a bad U-Boot design on other projects.
> 
> Please, come up with a concept that makes sense.

This is the same situation as above, where we need to see about pushing
some changes upstream perhaps.

-- 
Tom

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Re: [PATCH] doc: Add documentation about devicetree usage

[Bin Meng]

Hi Simon,

On Sat, Aug 28, 2021 at 11:23 AM Simon Glass <sjg@chromium.org> wrote:
>
> At present some of the ideas and techniques behind devicetree in U-Boot
> are assumed, implied or unsaid. Add some documentation to cover how
> devicetree is build, how it can be modified and the rules about using
> the various CONFIG_OF_... options.
>
> Signed-off-by: Simon Glass <sjg@chromium.org>
> ---
>
>  doc/develop/index.rst              |   1 +
>  doc/develop/package/devicetree.rst | 315 +++++++++++++++++++++++++++++
>  doc/develop/package/index.rst      |   1 +
>  3 files changed, 317 insertions(+)
>  create mode 100644 doc/develop/package/devicetree.rst
>
> diff --git a/doc/develop/index.rst b/doc/develop/index.rst
> index 83c929babda..d5ad8f9fe53 100644
> --- a/doc/develop/index.rst
> +++ b/doc/develop/index.rst
> @@ -36,6 +36,7 @@ Packaging
>     :maxdepth: 1
>
>     package/index
> +   package/devicetree
>
>  Testing
>  -------
> diff --git a/doc/develop/package/devicetree.rst b/doc/develop/package/devicetree.rst
> new file mode 100644
> index 00000000000..fccbb182f3e
> --- /dev/null
> +++ b/doc/develop/package/devicetree.rst
> @@ -0,0 +1,315 @@
> +.. SPDX-License-Identifier: GPL-2.0+
> +
> +Updating the devicetree
> +=======================
> +
> +U-Boot uses devicetree for runtime configuration and storing required blobs or
> +any other information it needs to operate. It is possible to update the
> +devicetree separately from actually building U-Boot. This provides a good degree
> +of control and flexibility for firmware that uses U-Boot in conjunction with
> +other project.
> +
> +There are many reasons why it is useful to modify the devicetree after building
> +it:
> +
> +- Configuration can be changed, e.g. which UART to use
> +- A serial number can be added
> +- Public keys can be added to allow image verification
> +- Console output can be changed (e.g. to select serial or vidconsole)
> +
> +This section describes how to work with devicetree to accomplish your goals.
> +
> +See also :doc:`../devicetree/control` for a basic summary of the available
> +features.
> +
> +
> +Devicetree source
> +-----------------
> +
> +Every board in U-Boot must include a devicetree sufficient to build and boot
> +that board on suitable hardware (or emulation). This is specified using the
> +`CONFIG DEFAULT_DEVICE_TREE` option.
> +
> +
> +Current situation (August 2021)
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +As an aside, at present U-Boot allows `CONFIG_DEFAULT_DEVICE_TREE` to be empty,
> +e.g. if `CONFIG_OF_BOARD` or `CONFIG_OF_PRIOR_STAGE` are used. This has
> +unfortunately created an enormous amount of confusion and some wasted effort.
> +This was not intended and this bug will be fixed soon. Specifically:
> +
> +- `CONFIG_OF_BOARD` was added in rpi_patch_ for Raspberry Pi, which does have
> +  an in-tree devicetree, but this feature has since been used for boards that
> +  don't
> +- `CONFIG_OF_PRIOR_STAGE` was added in bcm_patch_ as part of a larger Broadcom
> +  change with a tag indicating it only affected one board, so the change in
> +  behaviour was not noticed at the time. It has since been used by RISC-V qemu
> +  boards.
> +
> +Once this bug is fixed, CONFIG_OF_BOARD and CONFIG_OF_PRIOR_STAGE will override
> +(at runtime) the devicetree suppled with U-Boot, but will otherwise use
> +CONFIG_OF_SEPARATE for the in-tree build. So these two will become options,
> +moving out of the 'choice' in `dts/Kconfig`
> +
> +Offending boards are:
> +
> +- bcm7260
> +- bcm7445
> +- qemu_arm64
> +- qemu_arm
> +- qemu-ppce500
> +- qemu-riscv32
> +- qemu-riscv32_smode
> +- qemu-riscv64
> +- qemu-riscv64_smode
> +
> +All of these need to have a devicetree added in-tree. This is targeted to be
> +fixed in the 2022.01 release.

Do you have some idea of how to support the QEMU case, if not using
CONFIG_OF_PRIOR_STAGE?

Regards,
Bin

Re: [PATCH] doc: Add documentation about devicetree usage

[Heinrich Schuchardt]

On 8/28/21 3:01 PM, Tom Rini wrote:
> On Sat, Aug 28, 2021 at 02:29:21PM +0200, Heinrich Schuchardt wrote:
>> On 8/28/21 5:23 AM, Simon Glass wrote:
>>> At present some of the ideas and techniques behind devicetree in U-Boot
>>> are assumed, implied or unsaid. Add some documentation to cover how
>>> devicetree is build, how it can be modified and the rules about using
>>> the various CONFIG_OF_... options.
>>>
>>> Signed-off-by: Simon Glass <sjg@chromium.org>
>>> ---
>>>
>>>    doc/develop/index.rst              |   1 +
>>>    doc/develop/package/devicetree.rst | 315 +++++++++++++++++++++++++++++
>>>    doc/develop/package/index.rst      |   1 +
>>>    3 files changed, 317 insertions(+)
>>>    create mode 100644 doc/develop/package/devicetree.rst
>>>
>>> diff --git a/doc/develop/index.rst b/doc/develop/index.rst
>>> index 83c929babda..d5ad8f9fe53 100644
>>> --- a/doc/develop/index.rst
>>> +++ b/doc/develop/index.rst
>>> @@ -36,6 +36,7 @@ Packaging
>>>       :maxdepth: 1
>>>
>>>       package/index
>>> +   package/devicetree
>>>
>>>    Testing
>>>    -------
>>> diff --git a/doc/develop/package/devicetree.rst b/doc/develop/package/devicetree.rst
>>> new file mode 100644
>>> index 00000000000..fccbb182f3e
>>> --- /dev/null
>>> +++ b/doc/develop/package/devicetree.rst
>>> @@ -0,0 +1,315 @@
>>> +.. SPDX-License-Identifier: GPL-2.0+
>>> +
>>> +Updating the devicetree
>>> +=======================
>>> +
>>> +U-Boot uses devicetree for runtime configuration and storing required blobs or
>>> +any other information it needs to operate. It is possible to update the
>>> +devicetree separately from actually building U-Boot. This provides a good degree
>>> +of control and flexibility for firmware that uses U-Boot in conjunction with
>>> +other project.
>>> +
>>> +There are many reasons why it is useful to modify the devicetree after building
>>> +it:
>>> +
>>> +- Configuration can be changed, e.g. which UART to use
>>> +- A serial number can be added
>>> +- Public keys can be added to allow image verification
>>> +- Console output can be changed (e.g. to select serial or vidconsole)
>>> +
>>> +This section describes how to work with devicetree to accomplish your goals.
>>> +
>>> +See also :doc:`../devicetree/control` for a basic summary of the available
>>> +features.
>>> +
>>> +
>>> +Devicetree source
>>> +-----------------
>>> +
>>> +Every board in U-Boot must include a devicetree sufficient to build and boot
>>> +that board on suitable hardware (or emulation). This is specified using the
>>> +`CONFIG DEFAULT_DEVICE_TREE` option.
>>> +
>>> +
>>> +Current situation (August 2021)
>>> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>> +
>>> +As an aside, at present U-Boot allows `CONFIG_DEFAULT_DEVICE_TREE` to be empty,
>>> +e.g. if `CONFIG_OF_BOARD` or `CONFIG_OF_PRIOR_STAGE` are used. This has
>>> +unfortunately created an enormous amount of confusion and some wasted effort.
>>> +This was not intended and this bug will be fixed soon. Specifically:
>>> +
>>> +- `CONFIG_OF_BOARD` was added in rpi_patch_ for Raspberry Pi, which does have
>>> +  an in-tree devicetree, but this feature has since been used for boards that
>>> +  don't
>>> +- `CONFIG_OF_PRIOR_STAGE` was added in bcm_patch_ as part of a larger Broadcom
>>> +  change with a tag indicating it only affected one board, so the change in
>>> +  behaviour was not noticed at the time. It has since been used by RISC-V qemu
>>> +  boards.
>>> +
>>> +Once this bug is fixed, CONFIG_OF_BOARD and CONFIG_OF_PRIOR_STAGE will override
>>> +(at runtime) the devicetree suppled with U-Boot, but will otherwise use
>>> +CONFIG_OF_SEPARATE for the in-tree build. So these two will become options,
>>> +moving out of the 'choice' in `dts/Kconfig`
>>> +
>>> +Offending boards are:
>>> +
>>> +- bcm7260
>>> +- bcm7445
>>> +- qemu_arm64
>>> +- qemu_arm
>>> +- qemu-ppce500
>>> +- qemu-riscv32
>>> +- qemu-riscv32_smode
>>> +- qemu-riscv64
>>> +- qemu-riscv64_smode
>>> +
>>> +All of these need to have a devicetree added in-tree. This is targeted to be
>>> +fixed in the 2022.01 release.
>>> +
>>> +
>>> +Building the devicetree
>>> +-----------------------
>>> +
>>> +U-Boot automatically builds the devicetree for a board, from the
>>> +`arch/<arch>/dts` directory. The Makefile in those directories has rules for
>>> +building devicetree files. It is preferable to avoid target-specific rules in
>>> +those files: i.e. all boards for a particular SoC should be built at once,
>>> +where practical. Apart from simplifying the Makefile, this helps to efficiently
>>> +(and immediately) ensure that changes in one board's DT do not break others that
>>> +are related. Building devicetrees is fast, so performance is seldom a concern
>>> +here.
>>> +
>>> +
>>> +Overriding the default devicetree
>>> +---------------------------------
>>> +
>>> +When building U-Boot, the `DEVICE_TREE` environment variable allows the
>>> +default devicetree file to be overridden at build time. This can be useful if
>>> +modifications have to be made to the in-tree devicetree file, for the benefit
>>> +of a downstream build system. Note that the in-tree devicetree must be
>>> +sufficient to build and boot, so this is not a way to bypass that requirement.
>>> +
>>> +
>>> +Modifying the devicetree after building
>>> +---------------------------------------
>>> +
>>> +While it is generally painful and hacky to modify the code or rodata of a
>>> +program after it is built, in many cases it is useul to do so, e.g. to add
>>> +configuration information like serial numbers, enabling/disabling features, etc.
>>> +
>>> +Devicetree provides a very nice solution to these problems since it is
>>> +structured data and it is relatively easy to change it, even in binary form
>>> +(see fdtput).
>>> +
>>> +U-Boot takes care that the devicetree is easily accessible after the build
>>> +process. In fact it is placed in a separate file called `u-boot.dtb`. If the
>>> +build system wants to modify or replace that file, it can do so. Then all that
>>> +is needed is to run `binman update` to update the file inside the image. If
>>> +binman is not used, then `u-boot-nodtb.bin` and the new `u-boot.dtb` can simply
>>> +be concatenated to achieve the desired result. U-Boot happily copes with the
>>> +devicetree growing or shrinking.
>>> +
>>> +The `u-boot.bin` image contains both pieces. While it is possible to locate the
>>> +devicetree within the image using the signature at the start of the file, this
>>> +is a bit messy.
>>> +
>>> +This is why `CONFIG_OF_SEPARATE` should always be used when building U-Boot.
>>> +The `CONFIG_OF_EMBED` option embeds the devicetree somewhere in the U-Boot ELF
>>> +image as rodata, meaning that it is hard to find it and it cannot increase in
>>> +size.
>>> +
>>> +When modifying the devicetree, the different cases to consider are as follows:
>>> +
>>> +- CONFIG_OF_SEPARATE
>>> +    This is easy, described above. Just change, replace or rebuild the
>>> +    devicetree so it suits your needs, then rerun binman or redo the `cat`
>>> +    operation to join `u-boot-nodtb.bin` and the new `u-boot.dtb`
>>> +
>>> +- CONFIG_OF_EMBD
>>> +    This is tricky, since the devicetree cannot easily be located. If the EFL
>>> +    file is available, then the _dtb_dt_begin and __dtb_dt_end symbols can be
>>> +    examined to find it. While it is possible to contract the file, it is not
>>> +    possible to expand the file since that would involve re-linking
>>> +
>>> +- CONFIG_OF_PRIOR_STAGE
>>> +    In this case the devicetree must be modified in the project which provides
>>> +    it, as described below
>>> +
>>> +- CONFIG_OF_BOARD
>>> +    This is a board-specific situation, so needs to be considered on a
>>> +    case-by-case base. The devicetree must be modified so that the correct
>>> +    one is provided to U-Boot. How this is done depends entirely on the
>>> +    implementation of this option for the board. It might require injecting the
>>> +    changes into a different project somehow using tooling available there, or
>>> +    it might involve merging an overlay file at runtime to obtain the desired
>>> +    result.
>>> +
>>> +
>>> +Devicetree in another project
>>> +-----------------------------
>>> +
>>> +In some cases U-Boot receive its devicetree at runtime from a program that calls
>>> +it. For example ARM's Trusted Firmware A (`TF-A`_) may have a devicetree that it
>>> +passes to U-Boot. This overrides any devicetree build by U-Boot. When packaging
>>> +the firmware, the U-Boot devicetree may in fact be left out if it can be
>>> +guaranteed that it will receive one from another project.
>>> +
>>> +In this case, the devicetree in the other project must track U-Boot's use of
>>> +device tree. It must provide a way to add configuration and other information to
>>
>> U-Boot does not rule the world. So never ever is this going to happen.
>> It is the other way round. U-Boot must consume what the prior bootstage
>> delivers. If U-Boot needs extra nodes it has to provide these on its own.
>>
>> Please, remove this assumption from the document.
>
> We need to figure out which compatibles we need to push upstream, and
> which we need to see if we can solve another way.
>
>>> +the devicetree for use by U-Boot, such as the /config node. Note that the
>>> +U-Boot in-tree devicetree must be sufficient to build and boot, so this is not a
>>> +way to bypass that requirement.
>>> +
>>> +If binman is used, the in-tree U-Boot devicetree must contain the binman
>>> +definition so that a valid image can be build.
>>
>> No clue what an in-tree tree might be. Please, avoid such confusing
>> language.
>
> Would "source tree devicetree" be less confusing?  Or can you suggest an
> alternative?
>
>>
>>> +
>>> +If verified boot is used, the project must provide a way to inject a public key,
>>
>> %s/the project/U-Boot/
>>
>>> +certificate or other material into the U-Boot devicetree so that it is available
>>> +to U-Boot at runtime. See `Signing with U-Boot devicetree`_. This may be
>>> +through tooling in the project itself or by making use of U-Boot's tooling.
>>> +
>>> +
>>> +Devicetree generated on-the-fly in another project
>>> +--------------------------------------------------
>
> I think this is a confusing topic, and gets things a bit backwards.
>
>>> +
>>> +In some rare cases, another project may wish to create a devicetree for U-Boot
>>> +entirely on-the-fly, then pass it to U-Boot at runtime. The only known example
>>> +of this at the time of writing (2021) is qemu, for ARM (`QEMU ARM`_) and
>>> +RISC-V (`QEMU RISC-V`_).
>
> What's the difference between QEMU and hardware that ships with a device
> tree stored in flash?  In both cases, we need to have the device tree
> that's provided be the device tree that works.  Like I was just raising
> in another thread, there are not multiple device trees for a given
> device, there is the device tree and it works for everyone that needs to
> consume a device tree.
>
>>> +In this case, the devicetree in the other project must track U-Boot's use of
>>> +device tree, so that it remains compatible. If a particular version of the
>>
>> Why? U-Boot must support its internal needs itself!
>>
>> Don't try to force a bad U-Boot design on other projects.
>>
>> Please, come up with a concept that makes sense.
>
> This is the same situation as above, where we need to see about pushing
> some changes upstream perhaps.
>

In U-Boot we currently have a lot of device-tree nodes that are
irrelevant for anything but U-Boot, e.g. all those nodes marked as
compatible to "u-boot,*". It does not make sense to push these upstream.

So if a prior bootstage provides a devicetree, we need a separate
devicetree in U-Boot.

We can copy the incoming devicetree to a private copy and amend all our
U-Boot specific stuff. Then let's use this private copy for
$fdt_control_addr and bringing up U-Boot while keeping the original
incoming devicetree as $fdt_addr so that we can pass it to the next boot
stage.

Best regards

Heinrich

Re: [PATCH] doc: Add documentation about devicetree usage

[Tom Rini]

[-- Attachment #1: Type: text/plain, Size: 13709 bytes --]

On Sat, Aug 28, 2021 at 03:30:15PM +0200, Heinrich Schuchardt wrote:
> On 8/28/21 3:01 PM, Tom Rini wrote:
> > On Sat, Aug 28, 2021 at 02:29:21PM +0200, Heinrich Schuchardt wrote:
> > > On 8/28/21 5:23 AM, Simon Glass wrote:
> > > > At present some of the ideas and techniques behind devicetree in U-Boot
> > > > are assumed, implied or unsaid. Add some documentation to cover how
> > > > devicetree is build, how it can be modified and the rules about using
> > > > the various CONFIG_OF_... options.
> > > > 
> > > > Signed-off-by: Simon Glass <sjg@chromium.org>
> > > > ---
> > > > 
> > > >    doc/develop/index.rst              |   1 +
> > > >    doc/develop/package/devicetree.rst | 315 +++++++++++++++++++++++++++++
> > > >    doc/develop/package/index.rst      |   1 +
> > > >    3 files changed, 317 insertions(+)
> > > >    create mode 100644 doc/develop/package/devicetree.rst
> > > > 
> > > > diff --git a/doc/develop/index.rst b/doc/develop/index.rst
> > > > index 83c929babda..d5ad8f9fe53 100644
> > > > --- a/doc/develop/index.rst
> > > > +++ b/doc/develop/index.rst
> > > > @@ -36,6 +36,7 @@ Packaging
> > > >       :maxdepth: 1
> > > > 
> > > >       package/index
> > > > +   package/devicetree
> > > > 
> > > >    Testing
> > > >    -------
> > > > diff --git a/doc/develop/package/devicetree.rst b/doc/develop/package/devicetree.rst
> > > > new file mode 100644
> > > > index 00000000000..fccbb182f3e
> > > > --- /dev/null
> > > > +++ b/doc/develop/package/devicetree.rst
> > > > @@ -0,0 +1,315 @@
> > > > +.. SPDX-License-Identifier: GPL-2.0+
> > > > +
> > > > +Updating the devicetree
> > > > +=======================
> > > > +
> > > > +U-Boot uses devicetree for runtime configuration and storing required blobs or
> > > > +any other information it needs to operate. It is possible to update the
> > > > +devicetree separately from actually building U-Boot. This provides a good degree
> > > > +of control and flexibility for firmware that uses U-Boot in conjunction with
> > > > +other project.
> > > > +
> > > > +There are many reasons why it is useful to modify the devicetree after building
> > > > +it:
> > > > +
> > > > +- Configuration can be changed, e.g. which UART to use
> > > > +- A serial number can be added
> > > > +- Public keys can be added to allow image verification
> > > > +- Console output can be changed (e.g. to select serial or vidconsole)
> > > > +
> > > > +This section describes how to work with devicetree to accomplish your goals.
> > > > +
> > > > +See also :doc:`../devicetree/control` for a basic summary of the available
> > > > +features.
> > > > +
> > > > +
> > > > +Devicetree source
> > > > +-----------------
> > > > +
> > > > +Every board in U-Boot must include a devicetree sufficient to build and boot
> > > > +that board on suitable hardware (or emulation). This is specified using the
> > > > +`CONFIG DEFAULT_DEVICE_TREE` option.
> > > > +
> > > > +
> > > > +Current situation (August 2021)
> > > > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > > +
> > > > +As an aside, at present U-Boot allows `CONFIG_DEFAULT_DEVICE_TREE` to be empty,
> > > > +e.g. if `CONFIG_OF_BOARD` or `CONFIG_OF_PRIOR_STAGE` are used. This has
> > > > +unfortunately created an enormous amount of confusion and some wasted effort.
> > > > +This was not intended and this bug will be fixed soon. Specifically:
> > > > +
> > > > +- `CONFIG_OF_BOARD` was added in rpi_patch_ for Raspberry Pi, which does have
> > > > +  an in-tree devicetree, but this feature has since been used for boards that
> > > > +  don't
> > > > +- `CONFIG_OF_PRIOR_STAGE` was added in bcm_patch_ as part of a larger Broadcom
> > > > +  change with a tag indicating it only affected one board, so the change in
> > > > +  behaviour was not noticed at the time. It has since been used by RISC-V qemu
> > > > +  boards.
> > > > +
> > > > +Once this bug is fixed, CONFIG_OF_BOARD and CONFIG_OF_PRIOR_STAGE will override
> > > > +(at runtime) the devicetree suppled with U-Boot, but will otherwise use
> > > > +CONFIG_OF_SEPARATE for the in-tree build. So these two will become options,
> > > > +moving out of the 'choice' in `dts/Kconfig`
> > > > +
> > > > +Offending boards are:
> > > > +
> > > > +- bcm7260
> > > > +- bcm7445
> > > > +- qemu_arm64
> > > > +- qemu_arm
> > > > +- qemu-ppce500
> > > > +- qemu-riscv32
> > > > +- qemu-riscv32_smode
> > > > +- qemu-riscv64
> > > > +- qemu-riscv64_smode
> > > > +
> > > > +All of these need to have a devicetree added in-tree. This is targeted to be
> > > > +fixed in the 2022.01 release.
> > > > +
> > > > +
> > > > +Building the devicetree
> > > > +-----------------------
> > > > +
> > > > +U-Boot automatically builds the devicetree for a board, from the
> > > > +`arch/<arch>/dts` directory. The Makefile in those directories has rules for
> > > > +building devicetree files. It is preferable to avoid target-specific rules in
> > > > +those files: i.e. all boards for a particular SoC should be built at once,
> > > > +where practical. Apart from simplifying the Makefile, this helps to efficiently
> > > > +(and immediately) ensure that changes in one board's DT do not break others that
> > > > +are related. Building devicetrees is fast, so performance is seldom a concern
> > > > +here.
> > > > +
> > > > +
> > > > +Overriding the default devicetree
> > > > +---------------------------------
> > > > +
> > > > +When building U-Boot, the `DEVICE_TREE` environment variable allows the
> > > > +default devicetree file to be overridden at build time. This can be useful if
> > > > +modifications have to be made to the in-tree devicetree file, for the benefit
> > > > +of a downstream build system. Note that the in-tree devicetree must be
> > > > +sufficient to build and boot, so this is not a way to bypass that requirement.
> > > > +
> > > > +
> > > > +Modifying the devicetree after building
> > > > +---------------------------------------
> > > > +
> > > > +While it is generally painful and hacky to modify the code or rodata of a
> > > > +program after it is built, in many cases it is useul to do so, e.g. to add
> > > > +configuration information like serial numbers, enabling/disabling features, etc.
> > > > +
> > > > +Devicetree provides a very nice solution to these problems since it is
> > > > +structured data and it is relatively easy to change it, even in binary form
> > > > +(see fdtput).
> > > > +
> > > > +U-Boot takes care that the devicetree is easily accessible after the build
> > > > +process. In fact it is placed in a separate file called `u-boot.dtb`. If the
> > > > +build system wants to modify or replace that file, it can do so. Then all that
> > > > +is needed is to run `binman update` to update the file inside the image. If
> > > > +binman is not used, then `u-boot-nodtb.bin` and the new `u-boot.dtb` can simply
> > > > +be concatenated to achieve the desired result. U-Boot happily copes with the
> > > > +devicetree growing or shrinking.
> > > > +
> > > > +The `u-boot.bin` image contains both pieces. While it is possible to locate the
> > > > +devicetree within the image using the signature at the start of the file, this
> > > > +is a bit messy.
> > > > +
> > > > +This is why `CONFIG_OF_SEPARATE` should always be used when building U-Boot.
> > > > +The `CONFIG_OF_EMBED` option embeds the devicetree somewhere in the U-Boot ELF
> > > > +image as rodata, meaning that it is hard to find it and it cannot increase in
> > > > +size.
> > > > +
> > > > +When modifying the devicetree, the different cases to consider are as follows:
> > > > +
> > > > +- CONFIG_OF_SEPARATE
> > > > +    This is easy, described above. Just change, replace or rebuild the
> > > > +    devicetree so it suits your needs, then rerun binman or redo the `cat`
> > > > +    operation to join `u-boot-nodtb.bin` and the new `u-boot.dtb`
> > > > +
> > > > +- CONFIG_OF_EMBD
> > > > +    This is tricky, since the devicetree cannot easily be located. If the EFL
> > > > +    file is available, then the _dtb_dt_begin and __dtb_dt_end symbols can be
> > > > +    examined to find it. While it is possible to contract the file, it is not
> > > > +    possible to expand the file since that would involve re-linking
> > > > +
> > > > +- CONFIG_OF_PRIOR_STAGE
> > > > +    In this case the devicetree must be modified in the project which provides
> > > > +    it, as described below
> > > > +
> > > > +- CONFIG_OF_BOARD
> > > > +    This is a board-specific situation, so needs to be considered on a
> > > > +    case-by-case base. The devicetree must be modified so that the correct
> > > > +    one is provided to U-Boot. How this is done depends entirely on the
> > > > +    implementation of this option for the board. It might require injecting the
> > > > +    changes into a different project somehow using tooling available there, or
> > > > +    it might involve merging an overlay file at runtime to obtain the desired
> > > > +    result.
> > > > +
> > > > +
> > > > +Devicetree in another project
> > > > +-----------------------------
> > > > +
> > > > +In some cases U-Boot receive its devicetree at runtime from a program that calls
> > > > +it. For example ARM's Trusted Firmware A (`TF-A`_) may have a devicetree that it
> > > > +passes to U-Boot. This overrides any devicetree build by U-Boot. When packaging
> > > > +the firmware, the U-Boot devicetree may in fact be left out if it can be
> > > > +guaranteed that it will receive one from another project.
> > > > +
> > > > +In this case, the devicetree in the other project must track U-Boot's use of
> > > > +device tree. It must provide a way to add configuration and other information to
> > > 
> > > U-Boot does not rule the world. So never ever is this going to happen.
> > > It is the other way round. U-Boot must consume what the prior bootstage
> > > delivers. If U-Boot needs extra nodes it has to provide these on its own.
> > > 
> > > Please, remove this assumption from the document.
> > 
> > We need to figure out which compatibles we need to push upstream, and
> > which we need to see if we can solve another way.
> > 
> > > > +the devicetree for use by U-Boot, such as the /config node. Note that the
> > > > +U-Boot in-tree devicetree must be sufficient to build and boot, so this is not a
> > > > +way to bypass that requirement.
> > > > +
> > > > +If binman is used, the in-tree U-Boot devicetree must contain the binman
> > > > +definition so that a valid image can be build.
> > > 
> > > No clue what an in-tree tree might be. Please, avoid such confusing
> > > language.
> > 
> > Would "source tree devicetree" be less confusing?  Or can you suggest an
> > alternative?
> > 
> > > 
> > > > +
> > > > +If verified boot is used, the project must provide a way to inject a public key,
> > > 
> > > %s/the project/U-Boot/
> > > 
> > > > +certificate or other material into the U-Boot devicetree so that it is available
> > > > +to U-Boot at runtime. See `Signing with U-Boot devicetree`_. This may be
> > > > +through tooling in the project itself or by making use of U-Boot's tooling.
> > > > +
> > > > +
> > > > +Devicetree generated on-the-fly in another project
> > > > +--------------------------------------------------
> > 
> > I think this is a confusing topic, and gets things a bit backwards.
> > 
> > > > +
> > > > +In some rare cases, another project may wish to create a devicetree for U-Boot
> > > > +entirely on-the-fly, then pass it to U-Boot at runtime. The only known example
> > > > +of this at the time of writing (2021) is qemu, for ARM (`QEMU ARM`_) and
> > > > +RISC-V (`QEMU RISC-V`_).
> > 
> > What's the difference between QEMU and hardware that ships with a device
> > tree stored in flash?  In both cases, we need to have the device tree
> > that's provided be the device tree that works.  Like I was just raising
> > in another thread, there are not multiple device trees for a given
> > device, there is the device tree and it works for everyone that needs to
> > consume a device tree.
> > 
> > > > +In this case, the devicetree in the other project must track U-Boot's use of
> > > > +device tree, so that it remains compatible. If a particular version of the
> > > 
> > > Why? U-Boot must support its internal needs itself!
> > > 
> > > Don't try to force a bad U-Boot design on other projects.
> > > 
> > > Please, come up with a concept that makes sense.
> > 
> > This is the same situation as above, where we need to see about pushing
> > some changes upstream perhaps.
> > 
> 
> In U-Boot we currently have a lot of device-tree nodes that are
> irrelevant for anything but U-Boot, e.g. all those nodes marked as
> compatible to "u-boot,*". It does not make sense to push these upstream.
> 
> So if a prior bootstage provides a devicetree, we need a separate
> devicetree in U-Boot.
> 
> We can copy the incoming devicetree to a private copy and amend all our
> U-Boot specific stuff. Then let's use this private copy for
> $fdt_control_addr and bringing up U-Boot while keeping the original
> incoming devicetree as $fdt_addr so that we can pass it to the next boot
> stage.

I'm not sure that's how this works?  The "linux" vendor prefix is for
Linux specific bindings and are expected to be present in the tree it
receives, and not fixed up and added at runtime.  But if you can proof
of concept out what your idea, I suspect that would work to resolve a
handful of problems all the same, so it would be good to see.

-- 
Tom

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Re: [PATCH] doc: Add documentation about devicetree usage

[Simon Glass]

Hi,

On Sat, 28 Aug 2021 at 07:39, Tom Rini <trini@konsulko.com> wrote:
>
> On Sat, Aug 28, 2021 at 03:30:15PM +0200, Heinrich Schuchardt wrote:
> > On 8/28/21 3:01 PM, Tom Rini wrote:
> > > On Sat, Aug 28, 2021 at 02:29:21PM +0200, Heinrich Schuchardt wrote:
> > > > On 8/28/21 5:23 AM, Simon Glass wrote:
> > > > > At present some of the ideas and techniques behind devicetree in U-Boot
> > > > > are assumed, implied or unsaid. Add some documentation to cover how
> > > > > devicetree is build, how it can be modified and the rules about using
> > > > > the various CONFIG_OF_... options.
> > > > >
> > > > > Signed-off-by: Simon Glass <sjg@chromium.org>
> > > > > ---
> > > > >
> > > > >    doc/develop/index.rst              |   1 +
> > > > >    doc/develop/package/devicetree.rst | 315 +++++++++++++++++++++++++++++
> > > > >    doc/develop/package/index.rst      |   1 +
> > > > >    3 files changed, 317 insertions(+)
> > > > >    create mode 100644 doc/develop/package/devicetree.rst
> > > > >
> > > > > diff --git a/doc/develop/index.rst b/doc/develop/index.rst
> > > > > index 83c929babda..d5ad8f9fe53 100644
> > > > > --- a/doc/develop/index.rst
> > > > > +++ b/doc/develop/index.rst
> > > > > @@ -36,6 +36,7 @@ Packaging
> > > > >       :maxdepth: 1
> > > > >
> > > > >       package/index
> > > > > +   package/devicetree
> > > > >
> > > > >    Testing
> > > > >    -------
> > > > > diff --git a/doc/develop/package/devicetree.rst b/doc/develop/package/devicetree.rst
> > > > > new file mode 100644
> > > > > index 00000000000..fccbb182f3e
> > > > > --- /dev/null
> > > > > +++ b/doc/develop/package/devicetree.rst
> > > > > @@ -0,0 +1,315 @@
> > > > > +.. SPDX-License-Identifier: GPL-2.0+
> > > > > +
> > > > > +Updating the devicetree
> > > > > +=======================
> > > > > +
> > > > > +U-Boot uses devicetree for runtime configuration and storing required blobs or
> > > > > +any other information it needs to operate. It is possible to update the
> > > > > +devicetree separately from actually building U-Boot. This provides a good degree
> > > > > +of control and flexibility for firmware that uses U-Boot in conjunction with
> > > > > +other project.
> > > > > +
> > > > > +There are many reasons why it is useful to modify the devicetree after building
> > > > > +it:
> > > > > +
> > > > > +- Configuration can be changed, e.g. which UART to use
> > > > > +- A serial number can be added
> > > > > +- Public keys can be added to allow image verification
> > > > > +- Console output can be changed (e.g. to select serial or vidconsole)
> > > > > +
> > > > > +This section describes how to work with devicetree to accomplish your goals.
> > > > > +
> > > > > +See also :doc:`../devicetree/control` for a basic summary of the available
> > > > > +features.
> > > > > +
> > > > > +
> > > > > +Devicetree source
> > > > > +-----------------
> > > > > +
> > > > > +Every board in U-Boot must include a devicetree sufficient to build and boot
> > > > > +that board on suitable hardware (or emulation). This is specified using the
> > > > > +`CONFIG DEFAULT_DEVICE_TREE` option.
> > > > > +
> > > > > +
> > > > > +Current situation (August 2021)
> > > > > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > > > +
> > > > > +As an aside, at present U-Boot allows `CONFIG_DEFAULT_DEVICE_TREE` to be empty,
> > > > > +e.g. if `CONFIG_OF_BOARD` or `CONFIG_OF_PRIOR_STAGE` are used. This has
> > > > > +unfortunately created an enormous amount of confusion and some wasted effort.
> > > > > +This was not intended and this bug will be fixed soon. Specifically:
> > > > > +
> > > > > +- `CONFIG_OF_BOARD` was added in rpi_patch_ for Raspberry Pi, which does have
> > > > > +  an in-tree devicetree, but this feature has since been used for boards that
> > > > > +  don't
> > > > > +- `CONFIG_OF_PRIOR_STAGE` was added in bcm_patch_ as part of a larger Broadcom
> > > > > +  change with a tag indicating it only affected one board, so the change in
> > > > > +  behaviour was not noticed at the time. It has since been used by RISC-V qemu
> > > > > +  boards.
> > > > > +
> > > > > +Once this bug is fixed, CONFIG_OF_BOARD and CONFIG_OF_PRIOR_STAGE will override
> > > > > +(at runtime) the devicetree suppled with U-Boot, but will otherwise use
> > > > > +CONFIG_OF_SEPARATE for the in-tree build. So these two will become options,
> > > > > +moving out of the 'choice' in `dts/Kconfig`
> > > > > +
> > > > > +Offending boards are:
> > > > > +
> > > > > +- bcm7260
> > > > > +- bcm7445
> > > > > +- qemu_arm64
> > > > > +- qemu_arm
> > > > > +- qemu-ppce500
> > > > > +- qemu-riscv32
> > > > > +- qemu-riscv32_smode
> > > > > +- qemu-riscv64
> > > > > +- qemu-riscv64_smode
> > > > > +
> > > > > +All of these need to have a devicetree added in-tree. This is targeted to be
> > > > > +fixed in the 2022.01 release.
> > > > > +
> > > > > +
> > > > > +Building the devicetree
> > > > > +-----------------------
> > > > > +
> > > > > +U-Boot automatically builds the devicetree for a board, from the
> > > > > +`arch/<arch>/dts` directory. The Makefile in those directories has rules for
> > > > > +building devicetree files. It is preferable to avoid target-specific rules in
> > > > > +those files: i.e. all boards for a particular SoC should be built at once,
> > > > > +where practical. Apart from simplifying the Makefile, this helps to efficiently
> > > > > +(and immediately) ensure that changes in one board's DT do not break others that
> > > > > +are related. Building devicetrees is fast, so performance is seldom a concern
> > > > > +here.
> > > > > +
> > > > > +
> > > > > +Overriding the default devicetree
> > > > > +---------------------------------
> > > > > +
> > > > > +When building U-Boot, the `DEVICE_TREE` environment variable allows the
> > > > > +default devicetree file to be overridden at build time. This can be useful if
> > > > > +modifications have to be made to the in-tree devicetree file, for the benefit
> > > > > +of a downstream build system. Note that the in-tree devicetree must be
> > > > > +sufficient to build and boot, so this is not a way to bypass that requirement.
> > > > > +
> > > > > +
> > > > > +Modifying the devicetree after building
> > > > > +---------------------------------------
> > > > > +
> > > > > +While it is generally painful and hacky to modify the code or rodata of a
> > > > > +program after it is built, in many cases it is useul to do so, e.g. to add
> > > > > +configuration information like serial numbers, enabling/disabling features, etc.
> > > > > +
> > > > > +Devicetree provides a very nice solution to these problems since it is
> > > > > +structured data and it is relatively easy to change it, even in binary form
> > > > > +(see fdtput).
> > > > > +
> > > > > +U-Boot takes care that the devicetree is easily accessible after the build
> > > > > +process. In fact it is placed in a separate file called `u-boot.dtb`. If the
> > > > > +build system wants to modify or replace that file, it can do so. Then all that
> > > > > +is needed is to run `binman update` to update the file inside the image. If
> > > > > +binman is not used, then `u-boot-nodtb.bin` and the new `u-boot.dtb` can simply
> > > > > +be concatenated to achieve the desired result. U-Boot happily copes with the
> > > > > +devicetree growing or shrinking.
> > > > > +
> > > > > +The `u-boot.bin` image contains both pieces. While it is possible to locate the
> > > > > +devicetree within the image using the signature at the start of the file, this
> > > > > +is a bit messy.
> > > > > +
> > > > > +This is why `CONFIG_OF_SEPARATE` should always be used when building U-Boot.
> > > > > +The `CONFIG_OF_EMBED` option embeds the devicetree somewhere in the U-Boot ELF
> > > > > +image as rodata, meaning that it is hard to find it and it cannot increase in
> > > > > +size.
> > > > > +
> > > > > +When modifying the devicetree, the different cases to consider are as follows:
> > > > > +
> > > > > +- CONFIG_OF_SEPARATE
> > > > > +    This is easy, described above. Just change, replace or rebuild the
> > > > > +    devicetree so it suits your needs, then rerun binman or redo the `cat`
> > > > > +    operation to join `u-boot-nodtb.bin` and the new `u-boot.dtb`
> > > > > +
> > > > > +- CONFIG_OF_EMBD
> > > > > +    This is tricky, since the devicetree cannot easily be located. If the EFL
> > > > > +    file is available, then the _dtb_dt_begin and __dtb_dt_end symbols can be
> > > > > +    examined to find it. While it is possible to contract the file, it is not
> > > > > +    possible to expand the file since that would involve re-linking
> > > > > +
> > > > > +- CONFIG_OF_PRIOR_STAGE
> > > > > +    In this case the devicetree must be modified in the project which provides
> > > > > +    it, as described below
> > > > > +
> > > > > +- CONFIG_OF_BOARD
> > > > > +    This is a board-specific situation, so needs to be considered on a
> > > > > +    case-by-case base. The devicetree must be modified so that the correct
> > > > > +    one is provided to U-Boot. How this is done depends entirely on the
> > > > > +    implementation of this option for the board. It might require injecting the
> > > > > +    changes into a different project somehow using tooling available there, or
> > > > > +    it might involve merging an overlay file at runtime to obtain the desired
> > > > > +    result.
> > > > > +
> > > > > +
> > > > > +Devicetree in another project
> > > > > +-----------------------------
> > > > > +
> > > > > +In some cases U-Boot receive its devicetree at runtime from a program that calls
> > > > > +it. For example ARM's Trusted Firmware A (`TF-A`_) may have a devicetree that it
> > > > > +passes to U-Boot. This overrides any devicetree build by U-Boot. When packaging
> > > > > +the firmware, the U-Boot devicetree may in fact be left out if it can be
> > > > > +guaranteed that it will receive one from another project.
> > > > > +
> > > > > +In this case, the devicetree in the other project must track U-Boot's use of
> > > > > +device tree. It must provide a way to add configuration and other information to
> > > >
> > > > U-Boot does not rule the world. So never ever is this going to happen.
> > > > It is the other way round. U-Boot must consume what the prior bootstage
> > > > delivers. If U-Boot needs extra nodes it has to provide these on its own.
> > > >
> > > > Please, remove this assumption from the document.
> > >
> > > We need to figure out which compatibles we need to push upstream, and
> > > which we need to see if we can solve another way.
> > >
> > > > > +the devicetree for use by U-Boot, such as the /config node. Note that the
> > > > > +U-Boot in-tree devicetree must be sufficient to build and boot, so this is not a
> > > > > +way to bypass that requirement.
> > > > > +
> > > > > +If binman is used, the in-tree U-Boot devicetree must contain the binman
> > > > > +definition so that a valid image can be build.
> > > >
> > > > No clue what an in-tree tree might be. Please, avoid such confusing
> > > > language.
> > >
> > > Would "source tree devicetree" be less confusing?  Or can you suggest an
> > > alternative?
> > >
> > > >
> > > > > +
> > > > > +If verified boot is used, the project must provide a way to inject a public key,
> > > >
> > > > %s/the project/U-Boot/
> > > >
> > > > > +certificate or other material into the U-Boot devicetree so that it is available
> > > > > +to U-Boot at runtime. See `Signing with U-Boot devicetree`_. This may be
> > > > > +through tooling in the project itself or by making use of U-Boot's tooling.
> > > > > +
> > > > > +
> > > > > +Devicetree generated on-the-fly in another project
> > > > > +--------------------------------------------------
> > >
> > > I think this is a confusing topic, and gets things a bit backwards.
> > >
> > > > > +
> > > > > +In some rare cases, another project may wish to create a devicetree for U-Boot
> > > > > +entirely on-the-fly, then pass it to U-Boot at runtime. The only known example
> > > > > +of this at the time of writing (2021) is qemu, for ARM (`QEMU ARM`_) and
> > > > > +RISC-V (`QEMU RISC-V`_).
> > >
> > > What's the difference between QEMU and hardware that ships with a device
> > > tree stored in flash?  In both cases, we need to have the device tree
> > > that's provided be the device tree that works.  Like I was just raising
> > > in another thread, there are not multiple device trees for a given
> > > device, there is the device tree and it works for everyone that needs to
> > > consume a device tree.
> > >
> > > > > +In this case, the devicetree in the other project must track U-Boot's use of
> > > > > +device tree, so that it remains compatible. If a particular version of the
> > > >
> > > > Why? U-Boot must support its internal needs itself!
> > > >
> > > > Don't try to force a bad U-Boot design on other projects.
> > > >
> > > > Please, come up with a concept that makes sense.
> > >
> > > This is the same situation as above, where we need to see about pushing
> > > some changes upstream perhaps.
> > >
> >
> > In U-Boot we currently have a lot of device-tree nodes that are
> > irrelevant for anything but U-Boot, e.g. all those nodes marked as
> > compatible to "u-boot,*". It does not make sense to push these upstream.
> >
> > So if a prior bootstage provides a devicetree, we need a separate
> > devicetree in U-Boot.
> >

> > We can copy the incoming devicetree to a private copy and amend all our
> > U-Boot specific stuff. Then let's use this private copy for
> > $fdt_control_addr and bringing up U-Boot while keeping the original
> > incoming devicetree as $fdt_addr so that we can pass it to the next boot
> > stage.
>
> I'm not sure that's how this works?  The "linux" vendor prefix is for
> Linux specific bindings and are expected to be present in the tree it
> receives, and not fixed up and added at runtime.  But if you can proof
> of concept out what your idea, I suspect that would work to resolve a
> handful of problems all the same, so it would be good to see.

Gosh, great comments all, thank you.

I am going to send a v2 with most addressed and then perhaps we can do
another round. It seems to me that the task here is to clearly
document and motivate the status quo and immediate needs. As to future
changes, who can say where things will go. But without a shared
understanding of where we are and why, every discussion takes forever.

Regards,
Simon

Re: [PATCH] doc: Add documentation about devicetree usage

[Simon Glass]

Hi Bin,

On Sat, 28 Aug 2021 at 07:15, Bin Meng <bmeng.cn@gmail.com> wrote:
>
> Hi Simon,
>
> On Sat, Aug 28, 2021 at 11:23 AM Simon Glass <sjg@chromium.org> wrote:
> >
> > At present some of the ideas and techniques behind devicetree in U-Boot
> > are assumed, implied or unsaid. Add some documentation to cover how
> > devicetree is build, how it can be modified and the rules about using
> > the various CONFIG_OF_... options.
> >
> > Signed-off-by: Simon Glass <sjg@chromium.org>
> > ---
> >
> >  doc/develop/index.rst              |   1 +
> >  doc/develop/package/devicetree.rst | 315 +++++++++++++++++++++++++++++
> >  doc/develop/package/index.rst      |   1 +
> >  3 files changed, 317 insertions(+)
> >  create mode 100644 doc/develop/package/devicetree.rst
> >
> > diff --git a/doc/develop/index.rst b/doc/develop/index.rst
> > index 83c929babda..d5ad8f9fe53 100644
> > --- a/doc/develop/index.rst
> > +++ b/doc/develop/index.rst
> > @@ -36,6 +36,7 @@ Packaging
> >     :maxdepth: 1
> >
> >     package/index
> > +   package/devicetree
> >
> >  Testing
> >  -------
> > diff --git a/doc/develop/package/devicetree.rst b/doc/develop/package/devicetree.rst
> > new file mode 100644
> > index 00000000000..fccbb182f3e
> > --- /dev/null
> > +++ b/doc/develop/package/devicetree.rst
> > @@ -0,0 +1,315 @@
> > +.. SPDX-License-Identifier: GPL-2.0+
> > +
> > +Updating the devicetree
> > +=======================
> > +
> > +U-Boot uses devicetree for runtime configuration and storing required blobs or
> > +any other information it needs to operate. It is possible to update the
> > +devicetree separately from actually building U-Boot. This provides a good degree
> > +of control and flexibility for firmware that uses U-Boot in conjunction with
> > +other project.
> > +
> > +There are many reasons why it is useful to modify the devicetree after building
> > +it:
> > +
> > +- Configuration can be changed, e.g. which UART to use
> > +- A serial number can be added
> > +- Public keys can be added to allow image verification
> > +- Console output can be changed (e.g. to select serial or vidconsole)
> > +
> > +This section describes how to work with devicetree to accomplish your goals.
> > +
> > +See also :doc:`../devicetree/control` for a basic summary of the available
> > +features.
> > +
> > +
> > +Devicetree source
> > +-----------------
> > +
> > +Every board in U-Boot must include a devicetree sufficient to build and boot
> > +that board on suitable hardware (or emulation). This is specified using the
> > +`CONFIG DEFAULT_DEVICE_TREE` option.
> > +
> > +
> > +Current situation (August 2021)
> > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > +
> > +As an aside, at present U-Boot allows `CONFIG_DEFAULT_DEVICE_TREE` to be empty,
> > +e.g. if `CONFIG_OF_BOARD` or `CONFIG_OF_PRIOR_STAGE` are used. This has
> > +unfortunately created an enormous amount of confusion and some wasted effort.
> > +This was not intended and this bug will be fixed soon. Specifically:
> > +
> > +- `CONFIG_OF_BOARD` was added in rpi_patch_ for Raspberry Pi, which does have
> > +  an in-tree devicetree, but this feature has since been used for boards that
> > +  don't
> > +- `CONFIG_OF_PRIOR_STAGE` was added in bcm_patch_ as part of a larger Broadcom
> > +  change with a tag indicating it only affected one board, so the change in
> > +  behaviour was not noticed at the time. It has since been used by RISC-V qemu
> > +  boards.
> > +
> > +Once this bug is fixed, CONFIG_OF_BOARD and CONFIG_OF_PRIOR_STAGE will override
> > +(at runtime) the devicetree suppled with U-Boot, but will otherwise use
> > +CONFIG_OF_SEPARATE for the in-tree build. So these two will become options,
> > +moving out of the 'choice' in `dts/Kconfig`
> > +
> > +Offending boards are:
> > +
> > +- bcm7260
> > +- bcm7445
> > +- qemu_arm64
> > +- qemu_arm
> > +- qemu-ppce500
> > +- qemu-riscv32
> > +- qemu-riscv32_smode
> > +- qemu-riscv64
> > +- qemu-riscv64_smode
> > +
> > +All of these need to have a devicetree added in-tree. This is targeted to be
> > +fixed in the 2022.01 release.
>
> Do you have some idea of how to support the QEMU case, if not using
> CONFIG_OF_PRIOR_STAGE?

To be clear, I am not planning to remove this option. It will still work.

But I do want to have an in-tree devicetree for all boards, and
someone will need to update qemu to support adding U-Boot
nodes/properties. It always has an array of options controlling what
it presents to BIOS/UEFI, for example, so this should not be too
controversial.

Regards,
Simon

Re: [PATCH] doc: Add documentation about devicetree usage

[Simon Glass]

Hi Heinrich,

On Sat, 28 Aug 2021 at 07:39, Tom Rini <trini@konsulko.com> wrote:
>
> On Sat, Aug 28, 2021 at 03:30:15PM +0200, Heinrich Schuchardt wrote:
> > On 8/28/21 3:01 PM, Tom Rini wrote:
> > > On Sat, Aug 28, 2021 at 02:29:21PM +0200, Heinrich Schuchardt wrote:
> > > > On 8/28/21 5:23 AM, Simon Glass wrote:
> > > > > At present some of the ideas and techniques behind devicetree in U-Boot
> > > > > are assumed, implied or unsaid. Add some documentation to cover how
> > > > > devicetree is build, how it can be modified and the rules about using
> > > > > the various CONFIG_OF_... options.
> > > > >
> > > > > Signed-off-by: Simon Glass <sjg@chromium.org>
> > > > > ---
> > > > >
> > > > >    doc/develop/index.rst              |   1 +
> > > > >    doc/develop/package/devicetree.rst | 315 +++++++++++++++++++++++++++++
> > > > >    doc/develop/package/index.rst      |   1 +
> > > > >    3 files changed, 317 insertions(+)
> > > > >    create mode 100644 doc/develop/package/devicetree.rst
> > > > >
> > > > > diff --git a/doc/develop/index.rst b/doc/develop/index.rst
> > > > > index 83c929babda..d5ad8f9fe53 100644
> > > > > --- a/doc/develop/index.rst
> > > > > +++ b/doc/develop/index.rst
> > > > > @@ -36,6 +36,7 @@ Packaging
> > > > >       :maxdepth: 1
> > > > >
> > > > >       package/index
> > > > > +   package/devicetree
> > > > >
> > > > >    Testing
> > > > >    -------
> > > > > diff --git a/doc/develop/package/devicetree.rst b/doc/develop/package/devicetree.rst
> > > > > new file mode 100644
> > > > > index 00000000000..fccbb182f3e
> > > > > --- /dev/null
> > > > > +++ b/doc/develop/package/devicetree.rst
> > > > > @@ -0,0 +1,315 @@
> > > > > +.. SPDX-License-Identifier: GPL-2.0+
> > > > > +
> > > > > +Updating the devicetree
> > > > > +=======================
> > > > > +
> > > > > +U-Boot uses devicetree for runtime configuration and storing required blobs or
> > > > > +any other information it needs to operate. It is possible to update the
> > > > > +devicetree separately from actually building U-Boot. This provides a good degree
> > > > > +of control and flexibility for firmware that uses U-Boot in conjunction with
> > > > > +other project.
> > > > > +
> > > > > +There are many reasons why it is useful to modify the devicetree after building
> > > > > +it:
> > > > > +
> > > > > +- Configuration can be changed, e.g. which UART to use
> > > > > +- A serial number can be added
> > > > > +- Public keys can be added to allow image verification
> > > > > +- Console output can be changed (e.g. to select serial or vidconsole)
> > > > > +
> > > > > +This section describes how to work with devicetree to accomplish your goals.
> > > > > +
> > > > > +See also :doc:`../devicetree/control` for a basic summary of the available
> > > > > +features.
> > > > > +
> > > > > +
> > > > > +Devicetree source
> > > > > +-----------------
> > > > > +
> > > > > +Every board in U-Boot must include a devicetree sufficient to build and boot
> > > > > +that board on suitable hardware (or emulation). This is specified using the
> > > > > +`CONFIG DEFAULT_DEVICE_TREE` option.
> > > > > +
> > > > > +
> > > > > +Current situation (August 2021)
> > > > > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > > > +
> > > > > +As an aside, at present U-Boot allows `CONFIG_DEFAULT_DEVICE_TREE` to be empty,
> > > > > +e.g. if `CONFIG_OF_BOARD` or `CONFIG_OF_PRIOR_STAGE` are used. This has
> > > > > +unfortunately created an enormous amount of confusion and some wasted effort.
> > > > > +This was not intended and this bug will be fixed soon. Specifically:
> > > > > +
> > > > > +- `CONFIG_OF_BOARD` was added in rpi_patch_ for Raspberry Pi, which does have
> > > > > +  an in-tree devicetree, but this feature has since been used for boards that
> > > > > +  don't
> > > > > +- `CONFIG_OF_PRIOR_STAGE` was added in bcm_patch_ as part of a larger Broadcom
> > > > > +  change with a tag indicating it only affected one board, so the change in
> > > > > +  behaviour was not noticed at the time. It has since been used by RISC-V qemu
> > > > > +  boards.
> > > > > +
> > > > > +Once this bug is fixed, CONFIG_OF_BOARD and CONFIG_OF_PRIOR_STAGE will override
> > > > > +(at runtime) the devicetree suppled with U-Boot, but will otherwise use
> > > > > +CONFIG_OF_SEPARATE for the in-tree build. So these two will become options,
> > > > > +moving out of the 'choice' in `dts/Kconfig`
> > > > > +
> > > > > +Offending boards are:
> > > > > +
> > > > > +- bcm7260
> > > > > +- bcm7445
> > > > > +- qemu_arm64
> > > > > +- qemu_arm
> > > > > +- qemu-ppce500
> > > > > +- qemu-riscv32
> > > > > +- qemu-riscv32_smode
> > > > > +- qemu-riscv64
> > > > > +- qemu-riscv64_smode
> > > > > +
> > > > > +All of these need to have a devicetree added in-tree. This is targeted to be
> > > > > +fixed in the 2022.01 release.
> > > > > +
> > > > > +
> > > > > +Building the devicetree
> > > > > +-----------------------
> > > > > +
> > > > > +U-Boot automatically builds the devicetree for a board, from the
> > > > > +`arch/<arch>/dts` directory. The Makefile in those directories has rules for
> > > > > +building devicetree files. It is preferable to avoid target-specific rules in
> > > > > +those files: i.e. all boards for a particular SoC should be built at once,
> > > > > +where practical. Apart from simplifying the Makefile, this helps to efficiently
> > > > > +(and immediately) ensure that changes in one board's DT do not break others that
> > > > > +are related. Building devicetrees is fast, so performance is seldom a concern
> > > > > +here.
> > > > > +
> > > > > +
> > > > > +Overriding the default devicetree
> > > > > +---------------------------------
> > > > > +
> > > > > +When building U-Boot, the `DEVICE_TREE` environment variable allows the
> > > > > +default devicetree file to be overridden at build time. This can be useful if
> > > > > +modifications have to be made to the in-tree devicetree file, for the benefit
> > > > > +of a downstream build system. Note that the in-tree devicetree must be
> > > > > +sufficient to build and boot, so this is not a way to bypass that requirement.
> > > > > +
> > > > > +
> > > > > +Modifying the devicetree after building
> > > > > +---------------------------------------
> > > > > +
> > > > > +While it is generally painful and hacky to modify the code or rodata of a
> > > > > +program after it is built, in many cases it is useul to do so, e.g. to add
> > > > > +configuration information like serial numbers, enabling/disabling features, etc.
> > > > > +
> > > > > +Devicetree provides a very nice solution to these problems since it is
> > > > > +structured data and it is relatively easy to change it, even in binary form
> > > > > +(see fdtput).
> > > > > +
> > > > > +U-Boot takes care that the devicetree is easily accessible after the build
> > > > > +process. In fact it is placed in a separate file called `u-boot.dtb`. If the
> > > > > +build system wants to modify or replace that file, it can do so. Then all that
> > > > > +is needed is to run `binman update` to update the file inside the image. If
> > > > > +binman is not used, then `u-boot-nodtb.bin` and the new `u-boot.dtb` can simply
> > > > > +be concatenated to achieve the desired result. U-Boot happily copes with the
> > > > > +devicetree growing or shrinking.
> > > > > +
> > > > > +The `u-boot.bin` image contains both pieces. While it is possible to locate the
> > > > > +devicetree within the image using the signature at the start of the file, this
> > > > > +is a bit messy.
> > > > > +
> > > > > +This is why `CONFIG_OF_SEPARATE` should always be used when building U-Boot.
> > > > > +The `CONFIG_OF_EMBED` option embeds the devicetree somewhere in the U-Boot ELF
> > > > > +image as rodata, meaning that it is hard to find it and it cannot increase in
> > > > > +size.
> > > > > +
> > > > > +When modifying the devicetree, the different cases to consider are as follows:
> > > > > +
> > > > > +- CONFIG_OF_SEPARATE
> > > > > +    This is easy, described above. Just change, replace or rebuild the
> > > > > +    devicetree so it suits your needs, then rerun binman or redo the `cat`
> > > > > +    operation to join `u-boot-nodtb.bin` and the new `u-boot.dtb`
> > > > > +
> > > > > +- CONFIG_OF_EMBD
> > > > > +    This is tricky, since the devicetree cannot easily be located. If the EFL
> > > > > +    file is available, then the _dtb_dt_begin and __dtb_dt_end symbols can be
> > > > > +    examined to find it. While it is possible to contract the file, it is not
> > > > > +    possible to expand the file since that would involve re-linking
> > > > > +
> > > > > +- CONFIG_OF_PRIOR_STAGE
> > > > > +    In this case the devicetree must be modified in the project which provides
> > > > > +    it, as described below
> > > > > +
> > > > > +- CONFIG_OF_BOARD
> > > > > +    This is a board-specific situation, so needs to be considered on a
> > > > > +    case-by-case base. The devicetree must be modified so that the correct
> > > > > +    one is provided to U-Boot. How this is done depends entirely on the
> > > > > +    implementation of this option for the board. It might require injecting the
> > > > > +    changes into a different project somehow using tooling available there, or
> > > > > +    it might involve merging an overlay file at runtime to obtain the desired
> > > > > +    result.
> > > > > +
> > > > > +
> > > > > +Devicetree in another project
> > > > > +-----------------------------
> > > > > +
> > > > > +In some cases U-Boot receive its devicetree at runtime from a program that calls
> > > > > +it. For example ARM's Trusted Firmware A (`TF-A`_) may have a devicetree that it
> > > > > +passes to U-Boot. This overrides any devicetree build by U-Boot. When packaging
> > > > > +the firmware, the U-Boot devicetree may in fact be left out if it can be
> > > > > +guaranteed that it will receive one from another project.
> > > > > +
> > > > > +In this case, the devicetree in the other project must track U-Boot's use of
> > > > > +device tree. It must provide a way to add configuration and other information to
> > > >
> > > > U-Boot does not rule the world. So never ever is this going to happen.
> > > > It is the other way round. U-Boot must consume what the prior bootstage
> > > > delivers. If U-Boot needs extra nodes it has to provide these on its own.
> > > >
> > > > Please, remove this assumption from the document.
> > >
> > > We need to figure out which compatibles we need to push upstream, and
> > > which we need to see if we can solve another way.
> > >
> > > > > +the devicetree for use by U-Boot, such as the /config node. Note that the
> > > > > +U-Boot in-tree devicetree must be sufficient to build and boot, so this is not a
> > > > > +way to bypass that requirement.
> > > > > +
> > > > > +If binman is used, the in-tree U-Boot devicetree must contain the binman
> > > > > +definition so that a valid image can be build.
> > > >
> > > > No clue what an in-tree tree might be. Please, avoid such confusing
> > > > language.
> > >
> > > Would "source tree devicetree" be less confusing?  Or can you suggest an
> > > alternative?
> > >
> > > >
> > > > > +
> > > > > +If verified boot is used, the project must provide a way to inject a public key,
> > > >
> > > > %s/the project/U-Boot/
> > > >
> > > > > +certificate or other material into the U-Boot devicetree so that it is available
> > > > > +to U-Boot at runtime. See `Signing with U-Boot devicetree`_. This may be
> > > > > +through tooling in the project itself or by making use of U-Boot's tooling.
> > > > > +
> > > > > +
> > > > > +Devicetree generated on-the-fly in another project
> > > > > +--------------------------------------------------
> > >
> > > I think this is a confusing topic, and gets things a bit backwards.
> > >
> > > > > +
> > > > > +In some rare cases, another project may wish to create a devicetree for U-Boot
> > > > > +entirely on-the-fly, then pass it to U-Boot at runtime. The only known example
> > > > > +of this at the time of writing (2021) is qemu, for ARM (`QEMU ARM`_) and
> > > > > +RISC-V (`QEMU RISC-V`_).
> > >
> > > What's the difference between QEMU and hardware that ships with a device
> > > tree stored in flash?  In both cases, we need to have the device tree
> > > that's provided be the device tree that works.  Like I was just raising
> > > in another thread, there are not multiple device trees for a given
> > > device, there is the device tree and it works for everyone that needs to
> > > consume a device tree.
> > >
> > > > > +In this case, the devicetree in the other project must track U-Boot's use of
> > > > > +device tree, so that it remains compatible. If a particular version of the
> > > >
> > > > Why? U-Boot must support its internal needs itself!
> > > >
> > > > Don't try to force a bad U-Boot design on other projects.
> > > >
> > > > Please, come up with a concept that makes sense.
> > >
> > > This is the same situation as above, where we need to see about pushing
> > > some changes upstream perhaps.
> > >
> >
> > In U-Boot we currently have a lot of device-tree nodes that are
> > irrelevant for anything but U-Boot, e.g. all those nodes marked as
> > compatible to "u-boot,*". It does not make sense to push these upstream.
> >
> > So if a prior bootstage provides a devicetree, we need a separate
> > devicetree in U-Boot.
> >
> > We can copy the incoming devicetree to a private copy and amend all our
> > U-Boot specific stuff. Then let's use this private copy for
> > $fdt_control_addr and bringing up U-Boot while keeping the original
> > incoming devicetree as $fdt_addr so that we can pass it to the next boot
> > stage.
>
> I'm not sure that's how this works?  The "linux" vendor prefix is for
> Linux specific bindings and are expected to be present in the tree it
> receives, and not fixed up and added at runtime.  But if you can proof
> of concept out what your idea, I suspect that would work to resolve a
> handful of problems all the same, so it would be good to see.

I actually suggested a different approach: copy the DT before fixing
it up. This effectively happens already if OF_LIVE is enabled.

U-Boot obviously cannot 'amend all our U-Boot specific stuff' at
runtime unless that is available somewhere else (at runtime). I'll
address that point in the v2 series.

Should we require the Linux stuff to be in a separate DT also? :-)

Regards,
SImon

Re: [PATCH] doc: Add documentation about devicetree usage

[Bin Meng]

Hi Simon,

On Sun, Aug 29, 2021 at 12:45 AM Simon Glass <sjg@chromium.org> wrote:
>
> Hi Bin,
>
> On Sat, 28 Aug 2021 at 07:15, Bin Meng <bmeng.cn@gmail.com> wrote:
> >
> > Hi Simon,
> >
> > On Sat, Aug 28, 2021 at 11:23 AM Simon Glass <sjg@chromium.org> wrote:
> > >
> > > At present some of the ideas and techniques behind devicetree in U-Boot
> > > are assumed, implied or unsaid. Add some documentation to cover how
> > > devicetree is build, how it can be modified and the rules about using
> > > the various CONFIG_OF_... options.
> > >
> > > Signed-off-by: Simon Glass <sjg@chromium.org>
> > > ---
> > >
> > >  doc/develop/index.rst              |   1 +
> > >  doc/develop/package/devicetree.rst | 315 +++++++++++++++++++++++++++++
> > >  doc/develop/package/index.rst      |   1 +
> > >  3 files changed, 317 insertions(+)
> > >  create mode 100644 doc/develop/package/devicetree.rst
> > >
> > > diff --git a/doc/develop/index.rst b/doc/develop/index.rst
> > > index 83c929babda..d5ad8f9fe53 100644
> > > --- a/doc/develop/index.rst
> > > +++ b/doc/develop/index.rst
> > > @@ -36,6 +36,7 @@ Packaging
> > >     :maxdepth: 1
> > >
> > >     package/index
> > > +   package/devicetree
> > >
> > >  Testing
> > >  -------
> > > diff --git a/doc/develop/package/devicetree.rst b/doc/develop/package/devicetree.rst
> > > new file mode 100644
> > > index 00000000000..fccbb182f3e
> > > --- /dev/null
> > > +++ b/doc/develop/package/devicetree.rst
> > > @@ -0,0 +1,315 @@
> > > +.. SPDX-License-Identifier: GPL-2.0+
> > > +
> > > +Updating the devicetree
> > > +=======================
> > > +
> > > +U-Boot uses devicetree for runtime configuration and storing required blobs or
> > > +any other information it needs to operate. It is possible to update the
> > > +devicetree separately from actually building U-Boot. This provides a good degree
> > > +of control and flexibility for firmware that uses U-Boot in conjunction with
> > > +other project.
> > > +
> > > +There are many reasons why it is useful to modify the devicetree after building
> > > +it:
> > > +
> > > +- Configuration can be changed, e.g. which UART to use
> > > +- A serial number can be added
> > > +- Public keys can be added to allow image verification
> > > +- Console output can be changed (e.g. to select serial or vidconsole)
> > > +
> > > +This section describes how to work with devicetree to accomplish your goals.
> > > +
> > > +See also :doc:`../devicetree/control` for a basic summary of the available
> > > +features.
> > > +
> > > +
> > > +Devicetree source
> > > +-----------------
> > > +
> > > +Every board in U-Boot must include a devicetree sufficient to build and boot
> > > +that board on suitable hardware (or emulation). This is specified using the
> > > +`CONFIG DEFAULT_DEVICE_TREE` option.
> > > +
> > > +
> > > +Current situation (August 2021)
> > > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > +
> > > +As an aside, at present U-Boot allows `CONFIG_DEFAULT_DEVICE_TREE` to be empty,
> > > +e.g. if `CONFIG_OF_BOARD` or `CONFIG_OF_PRIOR_STAGE` are used. This has
> > > +unfortunately created an enormous amount of confusion and some wasted effort.
> > > +This was not intended and this bug will be fixed soon. Specifically:
> > > +
> > > +- `CONFIG_OF_BOARD` was added in rpi_patch_ for Raspberry Pi, which does have
> > > +  an in-tree devicetree, but this feature has since been used for boards that
> > > +  don't
> > > +- `CONFIG_OF_PRIOR_STAGE` was added in bcm_patch_ as part of a larger Broadcom
> > > +  change with a tag indicating it only affected one board, so the change in
> > > +  behaviour was not noticed at the time. It has since been used by RISC-V qemu
> > > +  boards.
> > > +
> > > +Once this bug is fixed, CONFIG_OF_BOARD and CONFIG_OF_PRIOR_STAGE will override
> > > +(at runtime) the devicetree suppled with U-Boot, but will otherwise use
> > > +CONFIG_OF_SEPARATE for the in-tree build. So these two will become options,
> > > +moving out of the 'choice' in `dts/Kconfig`
> > > +
> > > +Offending boards are:
> > > +
> > > +- bcm7260
> > > +- bcm7445
> > > +- qemu_arm64
> > > +- qemu_arm
> > > +- qemu-ppce500
> > > +- qemu-riscv32
> > > +- qemu-riscv32_smode
> > > +- qemu-riscv64
> > > +- qemu-riscv64_smode
> > > +
> > > +All of these need to have a devicetree added in-tree. This is targeted to be
> > > +fixed in the 2022.01 release.
> >
> > Do you have some idea of how to support the QEMU case, if not using
> > CONFIG_OF_PRIOR_STAGE?
>
> To be clear, I am not planning to remove this option. It will still work.
>
> But I do want to have an in-tree devicetree for all boards, and
> someone will need to update qemu to support adding U-Boot
> nodes/properties. It always has an array of options controlling what
> it presents to BIOS/UEFI, for example, so this should not be too
> controversial.

I think there is some misunderstanding.

Adding U-Boot nodes/properties is not a problem for QEMU, but the
thing is that these QEMU targets don't require U-Boot specific
nodes/properties. It's just that QEMU will generate the DTB on the fly
based on different command-line options, so the DTB is dynamic and we
can't hardcode one in the U-Boot tree.

My understanding is that we should remove CONFIG_OF_BOARD but keep
CONFIG_OF_PRIOR_STAGE for such use case like QEMU.

Regards,
Bin

Re: [PATCH] doc: Add documentation about devicetree usage

[Simon Glass]

Hi Bin,

On Sat, 28 Aug 2021 at 19:29, Bin Meng <bmeng.cn@gmail.com> wrote:
>
> Hi Simon,
>
> On Sun, Aug 29, 2021 at 12:45 AM Simon Glass <sjg@chromium.org> wrote:
> >
> > Hi Bin,
> >
> > On Sat, 28 Aug 2021 at 07:15, Bin Meng <bmeng.cn@gmail.com> wrote:
> > >
> > > Hi Simon,
> > >
> > > On Sat, Aug 28, 2021 at 11:23 AM Simon Glass <sjg@chromium.org> wrote:
> > > >
> > > > At present some of the ideas and techniques behind devicetree in U-Boot
> > > > are assumed, implied or unsaid. Add some documentation to cover how
> > > > devicetree is build, how it can be modified and the rules about using
> > > > the various CONFIG_OF_... options.
> > > >
> > > > Signed-off-by: Simon Glass <sjg@chromium.org>
> > > > ---
> > > >
> > > >  doc/develop/index.rst              |   1 +
> > > >  doc/develop/package/devicetree.rst | 315 +++++++++++++++++++++++++++++
> > > >  doc/develop/package/index.rst      |   1 +
> > > >  3 files changed, 317 insertions(+)
> > > >  create mode 100644 doc/develop/package/devicetree.rst
> > > >
> > > > diff --git a/doc/develop/index.rst b/doc/develop/index.rst
> > > > index 83c929babda..d5ad8f9fe53 100644
> > > > --- a/doc/develop/index.rst
> > > > +++ b/doc/develop/index.rst
> > > > @@ -36,6 +36,7 @@ Packaging
> > > >     :maxdepth: 1
> > > >
> > > >     package/index
> > > > +   package/devicetree
> > > >
> > > >  Testing
> > > >  -------
> > > > diff --git a/doc/develop/package/devicetree.rst b/doc/develop/package/devicetree.rst
> > > > new file mode 100644
> > > > index 00000000000..fccbb182f3e
> > > > --- /dev/null
> > > > +++ b/doc/develop/package/devicetree.rst
> > > > @@ -0,0 +1,315 @@
> > > > +.. SPDX-License-Identifier: GPL-2.0+
> > > > +
> > > > +Updating the devicetree
> > > > +=======================
> > > > +
> > > > +U-Boot uses devicetree for runtime configuration and storing required blobs or
> > > > +any other information it needs to operate. It is possible to update the
> > > > +devicetree separately from actually building U-Boot. This provides a good degree
> > > > +of control and flexibility for firmware that uses U-Boot in conjunction with
> > > > +other project.
> > > > +
> > > > +There are many reasons why it is useful to modify the devicetree after building
> > > > +it:
> > > > +
> > > > +- Configuration can be changed, e.g. which UART to use
> > > > +- A serial number can be added
> > > > +- Public keys can be added to allow image verification
> > > > +- Console output can be changed (e.g. to select serial or vidconsole)
> > > > +
> > > > +This section describes how to work with devicetree to accomplish your goals.
> > > > +
> > > > +See also :doc:`../devicetree/control` for a basic summary of the available
> > > > +features.
> > > > +
> > > > +
> > > > +Devicetree source
> > > > +-----------------
> > > > +
> > > > +Every board in U-Boot must include a devicetree sufficient to build and boot
> > > > +that board on suitable hardware (or emulation). This is specified using the
> > > > +`CONFIG DEFAULT_DEVICE_TREE` option.
> > > > +
> > > > +
> > > > +Current situation (August 2021)
> > > > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > > +
> > > > +As an aside, at present U-Boot allows `CONFIG_DEFAULT_DEVICE_TREE` to be empty,
> > > > +e.g. if `CONFIG_OF_BOARD` or `CONFIG_OF_PRIOR_STAGE` are used. This has
> > > > +unfortunately created an enormous amount of confusion and some wasted effort.
> > > > +This was not intended and this bug will be fixed soon. Specifically:
> > > > +
> > > > +- `CONFIG_OF_BOARD` was added in rpi_patch_ for Raspberry Pi, which does have
> > > > +  an in-tree devicetree, but this feature has since been used for boards that
> > > > +  don't
> > > > +- `CONFIG_OF_PRIOR_STAGE` was added in bcm_patch_ as part of a larger Broadcom
> > > > +  change with a tag indicating it only affected one board, so the change in
> > > > +  behaviour was not noticed at the time. It has since been used by RISC-V qemu
> > > > +  boards.
> > > > +
> > > > +Once this bug is fixed, CONFIG_OF_BOARD and CONFIG_OF_PRIOR_STAGE will override
> > > > +(at runtime) the devicetree suppled with U-Boot, but will otherwise use
> > > > +CONFIG_OF_SEPARATE for the in-tree build. So these two will become options,
> > > > +moving out of the 'choice' in `dts/Kconfig`
> > > > +
> > > > +Offending boards are:
> > > > +
> > > > +- bcm7260
> > > > +- bcm7445
> > > > +- qemu_arm64
> > > > +- qemu_arm
> > > > +- qemu-ppce500
> > > > +- qemu-riscv32
> > > > +- qemu-riscv32_smode
> > > > +- qemu-riscv64
> > > > +- qemu-riscv64_smode
> > > > +
> > > > +All of these need to have a devicetree added in-tree. This is targeted to be
> > > > +fixed in the 2022.01 release.
> > >
> > > Do you have some idea of how to support the QEMU case, if not using
> > > CONFIG_OF_PRIOR_STAGE?
> >
> > To be clear, I am not planning to remove this option. It will still work.
> >
> > But I do want to have an in-tree devicetree for all boards, and
> > someone will need to update qemu to support adding U-Boot
> > nodes/properties. It always has an array of options controlling what
> > it presents to BIOS/UEFI, for example, so this should not be too
> > controversial.
>
> I think there is some misunderstanding.
>
> Adding U-Boot nodes/properties is not a problem for QEMU, but the
> thing is that these QEMU targets don't require U-Boot specific
> nodes/properties. It's just that QEMU will generate the DTB on the fly
> based on different command-line options, so the DTB is dynamic and we
> can't hardcode one in the U-Boot tree.

That's fine, but I do want some sort of sample in the tree, like we
have for qemu-x86 and others. For some reason ARM and RISC-V don't
have one.

Also, QEMU needs a way to add properties and nodes that are specific
to U-Boot, since at present there is no way at all to pass these
through (/config node, u-boot,dm-xxx tags, etc.).

Perhaps something like the -dtb option that it already has, but just
for something to merge with what it uses.

>
> My understanding is that we should remove CONFIG_OF_BOARD but keep
> CONFIG_OF_PRIOR_STAGE for such use case like QEMU.

Fair enough if OF_BOARD is basically a duplicate. I'm actually not sure...

Regards,
SImon

Re: [PATCH] doc: Add documentation about devicetree usage

[Mark Kettenis]

> From: Simon Glass <sjg@chromium.org>
> Date: Sat, 28 Aug 2021 20:07:27 -0600
> 
> Hi Bin,
> 
> On Sat, 28 Aug 2021 at 19:29, Bin Meng <bmeng.cn@gmail.com> wrote:
> >
> > Hi Simon,
> >
> > On Sun, Aug 29, 2021 at 12:45 AM Simon Glass <sjg@chromium.org> wrote:
> > >
> > > Hi Bin,
> > >
> > > On Sat, 28 Aug 2021 at 07:15, Bin Meng <bmeng.cn@gmail.com> wrote:
> > > >
> > > > Hi Simon,
> > > >
> > > > On Sat, Aug 28, 2021 at 11:23 AM Simon Glass <sjg@chromium.org> wrote:
> > > > >
> > > > > At present some of the ideas and techniques behind devicetree in U-Boot
> > > > > are assumed, implied or unsaid. Add some documentation to cover how
> > > > > devicetree is build, how it can be modified and the rules about using
> > > > > the various CONFIG_OF_... options.
> > > > >
> > > > > Signed-off-by: Simon Glass <sjg@chromium.org>
> > > > > ---
> > > > >
> > > > >  doc/develop/index.rst              |   1 +
> > > > >  doc/develop/package/devicetree.rst | 315 +++++++++++++++++++++++++++++
> > > > >  doc/develop/package/index.rst      |   1 +
> > > > >  3 files changed, 317 insertions(+)
> > > > >  create mode 100644 doc/develop/package/devicetree.rst
> > > > >
> > > > > diff --git a/doc/develop/index.rst b/doc/develop/index.rst
> > > > > index 83c929babda..d5ad8f9fe53 100644
> > > > > --- a/doc/develop/index.rst
> > > > > +++ b/doc/develop/index.rst
> > > > > @@ -36,6 +36,7 @@ Packaging
> > > > >     :maxdepth: 1
> > > > >
> > > > >     package/index
> > > > > +   package/devicetree
> > > > >
> > > > >  Testing
> > > > >  -------
> > > > > diff --git a/doc/develop/package/devicetree.rst b/doc/develop/package/devicetree.rst
> > > > > new file mode 100644
> > > > > index 00000000000..fccbb182f3e
> > > > > --- /dev/null
> > > > > +++ b/doc/develop/package/devicetree.rst
> > > > > @@ -0,0 +1,315 @@
> > > > > +.. SPDX-License-Identifier: GPL-2.0+
> > > > > +
> > > > > +Updating the devicetree
> > > > > +=======================
> > > > > +
> > > > > +U-Boot uses devicetree for runtime configuration and storing required blobs or
> > > > > +any other information it needs to operate. It is possible to update the
> > > > > +devicetree separately from actually building U-Boot. This provides a good degree
> > > > > +of control and flexibility for firmware that uses U-Boot in conjunction with
> > > > > +other project.
> > > > > +
> > > > > +There are many reasons why it is useful to modify the devicetree after building
> > > > > +it:
> > > > > +
> > > > > +- Configuration can be changed, e.g. which UART to use
> > > > > +- A serial number can be added
> > > > > +- Public keys can be added to allow image verification
> > > > > +- Console output can be changed (e.g. to select serial or vidconsole)
> > > > > +
> > > > > +This section describes how to work with devicetree to accomplish your goals.
> > > > > +
> > > > > +See also :doc:`../devicetree/control` for a basic summary of the available
> > > > > +features.
> > > > > +
> > > > > +
> > > > > +Devicetree source
> > > > > +-----------------
> > > > > +
> > > > > +Every board in U-Boot must include a devicetree sufficient to build and boot
> > > > > +that board on suitable hardware (or emulation). This is specified using the
> > > > > +`CONFIG DEFAULT_DEVICE_TREE` option.
> > > > > +
> > > > > +
> > > > > +Current situation (August 2021)
> > > > > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > > > +
> > > > > +As an aside, at present U-Boot allows `CONFIG_DEFAULT_DEVICE_TREE` to be empty,
> > > > > +e.g. if `CONFIG_OF_BOARD` or `CONFIG_OF_PRIOR_STAGE` are used. This has
> > > > > +unfortunately created an enormous amount of confusion and some wasted effort.
> > > > > +This was not intended and this bug will be fixed soon. Specifically:
> > > > > +
> > > > > +- `CONFIG_OF_BOARD` was added in rpi_patch_ for Raspberry Pi, which does have
> > > > > +  an in-tree devicetree, but this feature has since been used for boards that
> > > > > +  don't
> > > > > +- `CONFIG_OF_PRIOR_STAGE` was added in bcm_patch_ as part of a larger Broadcom
> > > > > +  change with a tag indicating it only affected one board, so the change in
> > > > > +  behaviour was not noticed at the time. It has since been used by RISC-V qemu
> > > > > +  boards.
> > > > > +
> > > > > +Once this bug is fixed, CONFIG_OF_BOARD and CONFIG_OF_PRIOR_STAGE will override
> > > > > +(at runtime) the devicetree suppled with U-Boot, but will otherwise use
> > > > > +CONFIG_OF_SEPARATE for the in-tree build. So these two will become options,
> > > > > +moving out of the 'choice' in `dts/Kconfig`
> > > > > +
> > > > > +Offending boards are:
> > > > > +
> > > > > +- bcm7260
> > > > > +- bcm7445
> > > > > +- qemu_arm64
> > > > > +- qemu_arm
> > > > > +- qemu-ppce500
> > > > > +- qemu-riscv32
> > > > > +- qemu-riscv32_smode
> > > > > +- qemu-riscv64
> > > > > +- qemu-riscv64_smode
> > > > > +
> > > > > +All of these need to have a devicetree added in-tree. This is targeted to be
> > > > > +fixed in the 2022.01 release.
> > > >
> > > > Do you have some idea of how to support the QEMU case, if not using
> > > > CONFIG_OF_PRIOR_STAGE?
> > >
> > > To be clear, I am not planning to remove this option. It will still work.
> > >
> > > But I do want to have an in-tree devicetree for all boards, and
> > > someone will need to update qemu to support adding U-Boot
> > > nodes/properties. It always has an array of options controlling what
> > > it presents to BIOS/UEFI, for example, so this should not be too
> > > controversial.
> >
> > I think there is some misunderstanding.
> >
> > Adding U-Boot nodes/properties is not a problem for QEMU, but the
> > thing is that these QEMU targets don't require U-Boot specific
> > nodes/properties. It's just that QEMU will generate the DTB on the fly
> > based on different command-line options, so the DTB is dynamic and we
> > can't hardcode one in the U-Boot tree.
> 
> That's fine, but I do want some sort of sample in the tree, like we
> have for qemu-x86 and others. For some reason ARM and RISC-V don't
> have one.
> 
> Also, QEMU needs a way to add properties and nodes that are specific
> to U-Boot, since at present there is no way at all to pass these
> through (/config node, u-boot,dm-xxx tags, etc.).

I suppose some of the /config stuff could be nice and that the device
tree is indeed the most appropriate way to pass runtime options from
QEMU to U-Boot.  But I'd say U-Boot should still work (with reasonable
defaults) if no U-Boot specific options are present in the device
tree.

My understanding is that the u-boot,dm-xxx tags are for SPL.  It seems
that for most scenarios having where there is some prior firmware that
passes a device tree, SPL isn't used.  That certainly is the case for
QEMU, Raspberry Pi and my Apple M1 work.

> Perhaps something like the -dtb option that it already has, but just
> for something to merge with what it uses.
> 
> > My understanding is that we should remove CONFIG_OF_BOARD but keep
> > CONFIG_OF_PRIOR_STAGE for such use case like QEMU.
> 
> Fair enough if OF_BOARD is basically a duplicate. I'm actually not sure...
> 
> Regards,
> SImon

Re: [PATCH] doc: Add documentation about devicetree usage

[Simon Glass]

Hi Mark,

On Sun, 29 Aug 2021 at 02:19, Mark Kettenis <mark.kettenis@xs4all.nl> wrote:
>
> > From: Simon Glass <sjg@chromium.org>
> > Date: Sat, 28 Aug 2021 20:07:27 -0600
> >
> > Hi Bin,
> >
> > On Sat, 28 Aug 2021 at 19:29, Bin Meng <bmeng.cn@gmail.com> wrote:
> > >
> > > Hi Simon,
> > >
> > > On Sun, Aug 29, 2021 at 12:45 AM Simon Glass <sjg@chromium.org> wrote:
> > > >
> > > > Hi Bin,
> > > >
> > > > On Sat, 28 Aug 2021 at 07:15, Bin Meng <bmeng.cn@gmail.com> wrote:
> > > > >
> > > > > Hi Simon,
> > > > >
> > > > > On Sat, Aug 28, 2021 at 11:23 AM Simon Glass <sjg@chromium.org> wrote:
> > > > > >
> > > > > > At present some of the ideas and techniques behind devicetree in U-Boot
> > > > > > are assumed, implied or unsaid. Add some documentation to cover how
> > > > > > devicetree is build, how it can be modified and the rules about using
> > > > > > the various CONFIG_OF_... options.
> > > > > >
> > > > > > Signed-off-by: Simon Glass <sjg@chromium.org>
> > > > > > ---
> > > > > >
> > > > > >  doc/develop/index.rst              |   1 +
> > > > > >  doc/develop/package/devicetree.rst | 315 +++++++++++++++++++++++++++++
> > > > > >  doc/develop/package/index.rst      |   1 +
> > > > > >  3 files changed, 317 insertions(+)
> > > > > >  create mode 100644 doc/develop/package/devicetree.rst
> > > > > >
> > > > > > diff --git a/doc/develop/index.rst b/doc/develop/index.rst
> > > > > > index 83c929babda..d5ad8f9fe53 100644
> > > > > > --- a/doc/develop/index.rst
> > > > > > +++ b/doc/develop/index.rst
> > > > > > @@ -36,6 +36,7 @@ Packaging
> > > > > >     :maxdepth: 1
> > > > > >
> > > > > >     package/index
> > > > > > +   package/devicetree
> > > > > >
> > > > > >  Testing
> > > > > >  -------
> > > > > > diff --git a/doc/develop/package/devicetree.rst b/doc/develop/package/devicetree.rst
> > > > > > new file mode 100644
> > > > > > index 00000000000..fccbb182f3e
> > > > > > --- /dev/null
> > > > > > +++ b/doc/develop/package/devicetree.rst
> > > > > > @@ -0,0 +1,315 @@
> > > > > > +.. SPDX-License-Identifier: GPL-2.0+
> > > > > > +
> > > > > > +Updating the devicetree
> > > > > > +=======================
> > > > > > +
> > > > > > +U-Boot uses devicetree for runtime configuration and storing required blobs or
> > > > > > +any other information it needs to operate. It is possible to update the
> > > > > > +devicetree separately from actually building U-Boot. This provides a good degree
> > > > > > +of control and flexibility for firmware that uses U-Boot in conjunction with
> > > > > > +other project.
> > > > > > +
> > > > > > +There are many reasons why it is useful to modify the devicetree after building
> > > > > > +it:
> > > > > > +
> > > > > > +- Configuration can be changed, e.g. which UART to use
> > > > > > +- A serial number can be added
> > > > > > +- Public keys can be added to allow image verification
> > > > > > +- Console output can be changed (e.g. to select serial or vidconsole)
> > > > > > +
> > > > > > +This section describes how to work with devicetree to accomplish your goals.
> > > > > > +
> > > > > > +See also :doc:`../devicetree/control` for a basic summary of the available
> > > > > > +features.
> > > > > > +
> > > > > > +
> > > > > > +Devicetree source
> > > > > > +-----------------
> > > > > > +
> > > > > > +Every board in U-Boot must include a devicetree sufficient to build and boot
> > > > > > +that board on suitable hardware (or emulation). This is specified using the
> > > > > > +`CONFIG DEFAULT_DEVICE_TREE` option.
> > > > > > +
> > > > > > +
> > > > > > +Current situation (August 2021)
> > > > > > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > > > > +
> > > > > > +As an aside, at present U-Boot allows `CONFIG_DEFAULT_DEVICE_TREE` to be empty,
> > > > > > +e.g. if `CONFIG_OF_BOARD` or `CONFIG_OF_PRIOR_STAGE` are used. This has
> > > > > > +unfortunately created an enormous amount of confusion and some wasted effort.
> > > > > > +This was not intended and this bug will be fixed soon. Specifically:
> > > > > > +
> > > > > > +- `CONFIG_OF_BOARD` was added in rpi_patch_ for Raspberry Pi, which does have
> > > > > > +  an in-tree devicetree, but this feature has since been used for boards that
> > > > > > +  don't
> > > > > > +- `CONFIG_OF_PRIOR_STAGE` was added in bcm_patch_ as part of a larger Broadcom
> > > > > > +  change with a tag indicating it only affected one board, so the change in
> > > > > > +  behaviour was not noticed at the time. It has since been used by RISC-V qemu
> > > > > > +  boards.
> > > > > > +
> > > > > > +Once this bug is fixed, CONFIG_OF_BOARD and CONFIG_OF_PRIOR_STAGE will override
> > > > > > +(at runtime) the devicetree suppled with U-Boot, but will otherwise use
> > > > > > +CONFIG_OF_SEPARATE for the in-tree build. So these two will become options,
> > > > > > +moving out of the 'choice' in `dts/Kconfig`
> > > > > > +
> > > > > > +Offending boards are:
> > > > > > +
> > > > > > +- bcm7260
> > > > > > +- bcm7445
> > > > > > +- qemu_arm64
> > > > > > +- qemu_arm
> > > > > > +- qemu-ppce500
> > > > > > +- qemu-riscv32
> > > > > > +- qemu-riscv32_smode
> > > > > > +- qemu-riscv64
> > > > > > +- qemu-riscv64_smode
> > > > > > +
> > > > > > +All of these need to have a devicetree added in-tree. This is targeted to be
> > > > > > +fixed in the 2022.01 release.
> > > > >
> > > > > Do you have some idea of how to support the QEMU case, if not using
> > > > > CONFIG_OF_PRIOR_STAGE?
> > > >
> > > > To be clear, I am not planning to remove this option. It will still work.
> > > >
> > > > But I do want to have an in-tree devicetree for all boards, and
> > > > someone will need to update qemu to support adding U-Boot
> > > > nodes/properties. It always has an array of options controlling what
> > > > it presents to BIOS/UEFI, for example, so this should not be too
> > > > controversial.
> > >
> > > I think there is some misunderstanding.
> > >
> > > Adding U-Boot nodes/properties is not a problem for QEMU, but the
> > > thing is that these QEMU targets don't require U-Boot specific
> > > nodes/properties. It's just that QEMU will generate the DTB on the fly
> > > based on different command-line options, so the DTB is dynamic and we
> > > can't hardcode one in the U-Boot tree.
> >
> > That's fine, but I do want some sort of sample in the tree, like we
> > have for qemu-x86 and others. For some reason ARM and RISC-V don't
> > have one.
> >
> > Also, QEMU needs a way to add properties and nodes that are specific
> > to U-Boot, since at present there is no way at all to pass these
> > through (/config node, u-boot,dm-xxx tags, etc.).
>
> I suppose some of the /config stuff could be nice and that the device
> tree is indeed the most appropriate way to pass runtime options from
> QEMU to U-Boot.  But I'd say U-Boot should still work (with reasonable
> defaults) if no U-Boot specific options are present in the device
> tree.

Well I believe it does and actually I think CI currently checks
this.The config node is certainly optional. But it would not support
booting signed images, for example, without the public key.

>
> My understanding is that the u-boot,dm-xxx tags are for SPL.  It seems
> that for most scenarios having where there is some prior firmware that
> passes a device tree, SPL isn't used.  That certainly is the case for
> QEMU, Raspberry Pi and my Apple M1 work.

Yes that is true and I suppose is how things are able to work at present.

But I do see QMU for RISC-V with an SPL boot, although it is only
mentioned in the docs, so perhaps it is not in the CI yet. If there
are few enough devices and enough memory (and you don't care about
boot speed) then the u-boot,dm-xxx tags are not strictly necessary.
But then we are using QEMU in a somewhat unrealistic state.

>
> > Perhaps something like the -dtb option that it already has, but just
> > for something to merge with what it uses.
> >
> > > My understanding is that we should remove CONFIG_OF_BOARD but keep
> > > CONFIG_OF_PRIOR_STAGE for such use case like QEMU.
> >
> > Fair enough if OF_BOARD is basically a duplicate. I'm actually not sure...

Regards,
Simon

Re: [PATCH] doc: Add documentation about devicetree usage

[Bin Meng]

Hi Simon,

On Sun, Aug 29, 2021 at 9:03 PM Simon Glass <sjg@chromium.org> wrote:
>
> Hi Mark,
>
> On Sun, 29 Aug 2021 at 02:19, Mark Kettenis <mark.kettenis@xs4all.nl> wrote:
> >
> > > From: Simon Glass <sjg@chromium.org>
> > > Date: Sat, 28 Aug 2021 20:07:27 -0600
> > >
> > > Hi Bin,
> > >
> > > On Sat, 28 Aug 2021 at 19:29, Bin Meng <bmeng.cn@gmail.com> wrote:
> > > >
> > > > Hi Simon,
> > > >
> > > > On Sun, Aug 29, 2021 at 12:45 AM Simon Glass <sjg@chromium.org> wrote:
> > > > >
> > > > > Hi Bin,
> > > > >
> > > > > On Sat, 28 Aug 2021 at 07:15, Bin Meng <bmeng.cn@gmail.com> wrote:
> > > > > >
> > > > > > Hi Simon,
> > > > > >
> > > > > > On Sat, Aug 28, 2021 at 11:23 AM Simon Glass <sjg@chromium.org> wrote:
> > > > > > >
> > > > > > > At present some of the ideas and techniques behind devicetree in U-Boot
> > > > > > > are assumed, implied or unsaid. Add some documentation to cover how
> > > > > > > devicetree is build, how it can be modified and the rules about using
> > > > > > > the various CONFIG_OF_... options.
> > > > > > >
> > > > > > > Signed-off-by: Simon Glass <sjg@chromium.org>
> > > > > > > ---
> > > > > > >
> > > > > > >  doc/develop/index.rst              |   1 +
> > > > > > >  doc/develop/package/devicetree.rst | 315 +++++++++++++++++++++++++++++
> > > > > > >  doc/develop/package/index.rst      |   1 +
> > > > > > >  3 files changed, 317 insertions(+)
> > > > > > >  create mode 100644 doc/develop/package/devicetree.rst
> > > > > > >
> > > > > > > diff --git a/doc/develop/index.rst b/doc/develop/index.rst
> > > > > > > index 83c929babda..d5ad8f9fe53 100644
> > > > > > > --- a/doc/develop/index.rst
> > > > > > > +++ b/doc/develop/index.rst
> > > > > > > @@ -36,6 +36,7 @@ Packaging
> > > > > > >     :maxdepth: 1
> > > > > > >
> > > > > > >     package/index
> > > > > > > +   package/devicetree
> > > > > > >
> > > > > > >  Testing
> > > > > > >  -------
> > > > > > > diff --git a/doc/develop/package/devicetree.rst b/doc/develop/package/devicetree.rst
> > > > > > > new file mode 100644
> > > > > > > index 00000000000..fccbb182f3e
> > > > > > > --- /dev/null
> > > > > > > +++ b/doc/develop/package/devicetree.rst
> > > > > > > @@ -0,0 +1,315 @@
> > > > > > > +.. SPDX-License-Identifier: GPL-2.0+
> > > > > > > +
> > > > > > > +Updating the devicetree
> > > > > > > +=======================
> > > > > > > +
> > > > > > > +U-Boot uses devicetree for runtime configuration and storing required blobs or
> > > > > > > +any other information it needs to operate. It is possible to update the
> > > > > > > +devicetree separately from actually building U-Boot. This provides a good degree
> > > > > > > +of control and flexibility for firmware that uses U-Boot in conjunction with
> > > > > > > +other project.
> > > > > > > +
> > > > > > > +There are many reasons why it is useful to modify the devicetree after building
> > > > > > > +it:
> > > > > > > +
> > > > > > > +- Configuration can be changed, e.g. which UART to use
> > > > > > > +- A serial number can be added
> > > > > > > +- Public keys can be added to allow image verification
> > > > > > > +- Console output can be changed (e.g. to select serial or vidconsole)
> > > > > > > +
> > > > > > > +This section describes how to work with devicetree to accomplish your goals.
> > > > > > > +
> > > > > > > +See also :doc:`../devicetree/control` for a basic summary of the available
> > > > > > > +features.
> > > > > > > +
> > > > > > > +
> > > > > > > +Devicetree source
> > > > > > > +-----------------
> > > > > > > +
> > > > > > > +Every board in U-Boot must include a devicetree sufficient to build and boot
> > > > > > > +that board on suitable hardware (or emulation). This is specified using the
> > > > > > > +`CONFIG DEFAULT_DEVICE_TREE` option.
> > > > > > > +
> > > > > > > +
> > > > > > > +Current situation (August 2021)
> > > > > > > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > > > > > +
> > > > > > > +As an aside, at present U-Boot allows `CONFIG_DEFAULT_DEVICE_TREE` to be empty,
> > > > > > > +e.g. if `CONFIG_OF_BOARD` or `CONFIG_OF_PRIOR_STAGE` are used. This has
> > > > > > > +unfortunately created an enormous amount of confusion and some wasted effort.
> > > > > > > +This was not intended and this bug will be fixed soon. Specifically:
> > > > > > > +
> > > > > > > +- `CONFIG_OF_BOARD` was added in rpi_patch_ for Raspberry Pi, which does have
> > > > > > > +  an in-tree devicetree, but this feature has since been used for boards that
> > > > > > > +  don't
> > > > > > > +- `CONFIG_OF_PRIOR_STAGE` was added in bcm_patch_ as part of a larger Broadcom
> > > > > > > +  change with a tag indicating it only affected one board, so the change in
> > > > > > > +  behaviour was not noticed at the time. It has since been used by RISC-V qemu
> > > > > > > +  boards.
> > > > > > > +
> > > > > > > +Once this bug is fixed, CONFIG_OF_BOARD and CONFIG_OF_PRIOR_STAGE will override
> > > > > > > +(at runtime) the devicetree suppled with U-Boot, but will otherwise use
> > > > > > > +CONFIG_OF_SEPARATE for the in-tree build. So these two will become options,
> > > > > > > +moving out of the 'choice' in `dts/Kconfig`
> > > > > > > +
> > > > > > > +Offending boards are:
> > > > > > > +
> > > > > > > +- bcm7260
> > > > > > > +- bcm7445
> > > > > > > +- qemu_arm64
> > > > > > > +- qemu_arm
> > > > > > > +- qemu-ppce500
> > > > > > > +- qemu-riscv32
> > > > > > > +- qemu-riscv32_smode
> > > > > > > +- qemu-riscv64
> > > > > > > +- qemu-riscv64_smode
> > > > > > > +
> > > > > > > +All of these need to have a devicetree added in-tree. This is targeted to be
> > > > > > > +fixed in the 2022.01 release.
> > > > > >
> > > > > > Do you have some idea of how to support the QEMU case, if not using
> > > > > > CONFIG_OF_PRIOR_STAGE?
> > > > >
> > > > > To be clear, I am not planning to remove this option. It will still work.
> > > > >
> > > > > But I do want to have an in-tree devicetree for all boards, and
> > > > > someone will need to update qemu to support adding U-Boot
> > > > > nodes/properties. It always has an array of options controlling what
> > > > > it presents to BIOS/UEFI, for example, so this should not be too
> > > > > controversial.
> > > >
> > > > I think there is some misunderstanding.
> > > >
> > > > Adding U-Boot nodes/properties is not a problem for QEMU, but the
> > > > thing is that these QEMU targets don't require U-Boot specific
> > > > nodes/properties. It's just that QEMU will generate the DTB on the fly
> > > > based on different command-line options, so the DTB is dynamic and we
> > > > can't hardcode one in the U-Boot tree.
> > >
> > > That's fine, but I do want some sort of sample in the tree, like we
> > > have for qemu-x86 and others. For some reason ARM and RISC-V don't
> > > have one.
> > >
> > > Also, QEMU needs a way to add properties and nodes that are specific
> > > to U-Boot, since at present there is no way at all to pass these
> > > through (/config node, u-boot,dm-xxx tags, etc.).
> >
> > I suppose some of the /config stuff could be nice and that the device
> > tree is indeed the most appropriate way to pass runtime options from
> > QEMU to U-Boot.  But I'd say U-Boot should still work (with reasonable
> > defaults) if no U-Boot specific options are present in the device
> > tree.
>
> Well I believe it does and actually I think CI currently checks
> this.The config node is certainly optional. But it would not support
> booting signed images, for example, without the public key.
>
> >
> > My understanding is that the u-boot,dm-xxx tags are for SPL.  It seems
> > that for most scenarios having where there is some prior firmware that
> > passes a device tree, SPL isn't used.  That certainly is the case for
> > QEMU, Raspberry Pi and my Apple M1 work.
>
> Yes that is true and I suppose is how things are able to work at present.
>
> But I do see QMU for RISC-V with an SPL boot, although it is only
> mentioned in the docs, so perhaps it is not in the CI yet. If there
> are few enough devices and enough memory (and you don't care about
> boot speed) then the u-boot,dm-xxx tags are not strictly necessary.
> But then we are using QEMU in a somewhat unrealistic state.
>

RISC-V SPL is in CI testing. See qemu_riscv{32,64}_spl targets in the
u-boot/master and the recent patches for SiFive Unleashed.

Regards,
Bin

Re: [PATCH] doc: Add documentation about devicetree usage

[Tom Rini]

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On Sun, Aug 29, 2021 at 10:19:53AM +0200, Mark Kettenis wrote:
> > From: Simon Glass <sjg@chromium.org>
> > Date: Sat, 28 Aug 2021 20:07:27 -0600
> > 
> > Hi Bin,
> > 
> > On Sat, 28 Aug 2021 at 19:29, Bin Meng <bmeng.cn@gmail.com> wrote:
> > >
> > > Hi Simon,
> > >
> > > On Sun, Aug 29, 2021 at 12:45 AM Simon Glass <sjg@chromium.org> wrote:
> > > >
> > > > Hi Bin,
> > > >
> > > > On Sat, 28 Aug 2021 at 07:15, Bin Meng <bmeng.cn@gmail.com> wrote:
> > > > >
> > > > > Hi Simon,
> > > > >
> > > > > On Sat, Aug 28, 2021 at 11:23 AM Simon Glass <sjg@chromium.org> wrote:
> > > > > >
> > > > > > At present some of the ideas and techniques behind devicetree in U-Boot
> > > > > > are assumed, implied or unsaid. Add some documentation to cover how
> > > > > > devicetree is build, how it can be modified and the rules about using
> > > > > > the various CONFIG_OF_... options.
> > > > > >
> > > > > > Signed-off-by: Simon Glass <sjg@chromium.org>
> > > > > > ---
> > > > > >
> > > > > >  doc/develop/index.rst              |   1 +
> > > > > >  doc/develop/package/devicetree.rst | 315 +++++++++++++++++++++++++++++
> > > > > >  doc/develop/package/index.rst      |   1 +
> > > > > >  3 files changed, 317 insertions(+)
> > > > > >  create mode 100644 doc/develop/package/devicetree.rst
> > > > > >
> > > > > > diff --git a/doc/develop/index.rst b/doc/develop/index.rst
> > > > > > index 83c929babda..d5ad8f9fe53 100644
> > > > > > --- a/doc/develop/index.rst
> > > > > > +++ b/doc/develop/index.rst
> > > > > > @@ -36,6 +36,7 @@ Packaging
> > > > > >     :maxdepth: 1
> > > > > >
> > > > > >     package/index
> > > > > > +   package/devicetree
> > > > > >
> > > > > >  Testing
> > > > > >  -------
> > > > > > diff --git a/doc/develop/package/devicetree.rst b/doc/develop/package/devicetree.rst
> > > > > > new file mode 100644
> > > > > > index 00000000000..fccbb182f3e
> > > > > > --- /dev/null
> > > > > > +++ b/doc/develop/package/devicetree.rst
> > > > > > @@ -0,0 +1,315 @@
> > > > > > +.. SPDX-License-Identifier: GPL-2.0+
> > > > > > +
> > > > > > +Updating the devicetree
> > > > > > +=======================
> > > > > > +
> > > > > > +U-Boot uses devicetree for runtime configuration and storing required blobs or
> > > > > > +any other information it needs to operate. It is possible to update the
> > > > > > +devicetree separately from actually building U-Boot. This provides a good degree
> > > > > > +of control and flexibility for firmware that uses U-Boot in conjunction with
> > > > > > +other project.
> > > > > > +
> > > > > > +There are many reasons why it is useful to modify the devicetree after building
> > > > > > +it:
> > > > > > +
> > > > > > +- Configuration can be changed, e.g. which UART to use
> > > > > > +- A serial number can be added
> > > > > > +- Public keys can be added to allow image verification
> > > > > > +- Console output can be changed (e.g. to select serial or vidconsole)
> > > > > > +
> > > > > > +This section describes how to work with devicetree to accomplish your goals.
> > > > > > +
> > > > > > +See also :doc:`../devicetree/control` for a basic summary of the available
> > > > > > +features.
> > > > > > +
> > > > > > +
> > > > > > +Devicetree source
> > > > > > +-----------------
> > > > > > +
> > > > > > +Every board in U-Boot must include a devicetree sufficient to build and boot
> > > > > > +that board on suitable hardware (or emulation). This is specified using the
> > > > > > +`CONFIG DEFAULT_DEVICE_TREE` option.
> > > > > > +
> > > > > > +
> > > > > > +Current situation (August 2021)
> > > > > > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > > > > +
> > > > > > +As an aside, at present U-Boot allows `CONFIG_DEFAULT_DEVICE_TREE` to be empty,
> > > > > > +e.g. if `CONFIG_OF_BOARD` or `CONFIG_OF_PRIOR_STAGE` are used. This has
> > > > > > +unfortunately created an enormous amount of confusion and some wasted effort.
> > > > > > +This was not intended and this bug will be fixed soon. Specifically:
> > > > > > +
> > > > > > +- `CONFIG_OF_BOARD` was added in rpi_patch_ for Raspberry Pi, which does have
> > > > > > +  an in-tree devicetree, but this feature has since been used for boards that
> > > > > > +  don't
> > > > > > +- `CONFIG_OF_PRIOR_STAGE` was added in bcm_patch_ as part of a larger Broadcom
> > > > > > +  change with a tag indicating it only affected one board, so the change in
> > > > > > +  behaviour was not noticed at the time. It has since been used by RISC-V qemu
> > > > > > +  boards.
> > > > > > +
> > > > > > +Once this bug is fixed, CONFIG_OF_BOARD and CONFIG_OF_PRIOR_STAGE will override
> > > > > > +(at runtime) the devicetree suppled with U-Boot, but will otherwise use
> > > > > > +CONFIG_OF_SEPARATE for the in-tree build. So these two will become options,
> > > > > > +moving out of the 'choice' in `dts/Kconfig`
> > > > > > +
> > > > > > +Offending boards are:
> > > > > > +
> > > > > > +- bcm7260
> > > > > > +- bcm7445
> > > > > > +- qemu_arm64
> > > > > > +- qemu_arm
> > > > > > +- qemu-ppce500
> > > > > > +- qemu-riscv32
> > > > > > +- qemu-riscv32_smode
> > > > > > +- qemu-riscv64
> > > > > > +- qemu-riscv64_smode
> > > > > > +
> > > > > > +All of these need to have a devicetree added in-tree. This is targeted to be
> > > > > > +fixed in the 2022.01 release.
> > > > >
> > > > > Do you have some idea of how to support the QEMU case, if not using
> > > > > CONFIG_OF_PRIOR_STAGE?
> > > >
> > > > To be clear, I am not planning to remove this option. It will still work.
> > > >
> > > > But I do want to have an in-tree devicetree for all boards, and
> > > > someone will need to update qemu to support adding U-Boot
> > > > nodes/properties. It always has an array of options controlling what
> > > > it presents to BIOS/UEFI, for example, so this should not be too
> > > > controversial.
> > >
> > > I think there is some misunderstanding.
> > >
> > > Adding U-Boot nodes/properties is not a problem for QEMU, but the
> > > thing is that these QEMU targets don't require U-Boot specific
> > > nodes/properties. It's just that QEMU will generate the DTB on the fly
> > > based on different command-line options, so the DTB is dynamic and we
> > > can't hardcode one in the U-Boot tree.
> > 
> > That's fine, but I do want some sort of sample in the tree, like we
> > have for qemu-x86 and others. For some reason ARM and RISC-V don't
> > have one.
> > 
> > Also, QEMU needs a way to add properties and nodes that are specific
> > to U-Boot, since at present there is no way at all to pass these
> > through (/config node, u-boot,dm-xxx tags, etc.).
> 
> I suppose some of the /config stuff could be nice and that the device
> tree is indeed the most appropriate way to pass runtime options from
> QEMU to U-Boot.  But I'd say U-Boot should still work (with reasonable
> defaults) if no U-Boot specific options are present in the device
> tree.
> 
> My understanding is that the u-boot,dm-xxx tags are for SPL.  It seems
> that for most scenarios having where there is some prior firmware that
> passes a device tree, SPL isn't used.  That certainly is the case for
> QEMU, Raspberry Pi and my Apple M1 work.

This is key, for moving forward.  We need to be able to function wholly
and correctly with a device tree we are given by whatever stars "us"
off.  When we talk about QEMU, we need to keep in mind what QEMU is
being used for, as the use cases.   I feel like QEMU-as-QEMU really is
to enable CI and perhaps enable debug/development workflows.
QEMU-as-hardware (SiFive from Bin's recent patch, sabrelite that QEMU
6.1.0 supports, integrator, malta like we do today, and so on) should be
"let us act like it's the real hardware".  So if we're expecting a
device tree to have X in it, we need to work with whatever the relevant
upstreams are to have it.

-- 
Tom

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Re: [PATCH] doc: Add documentation about devicetree usage

[Tom Rini]

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On Sun, Aug 29, 2021 at 07:03:14AM -0600, Simon Glass wrote:
> Hi Mark,
> 
> On Sun, 29 Aug 2021 at 02:19, Mark Kettenis <mark.kettenis@xs4all.nl> wrote:
> >
> > > From: Simon Glass <sjg@chromium.org>
> > > Date: Sat, 28 Aug 2021 20:07:27 -0600
> > >
> > > Hi Bin,
> > >
> > > On Sat, 28 Aug 2021 at 19:29, Bin Meng <bmeng.cn@gmail.com> wrote:
> > > >
> > > > Hi Simon,
> > > >
> > > > On Sun, Aug 29, 2021 at 12:45 AM Simon Glass <sjg@chromium.org> wrote:
> > > > >
> > > > > Hi Bin,
> > > > >
> > > > > On Sat, 28 Aug 2021 at 07:15, Bin Meng <bmeng.cn@gmail.com> wrote:
> > > > > >
> > > > > > Hi Simon,
> > > > > >
> > > > > > On Sat, Aug 28, 2021 at 11:23 AM Simon Glass <sjg@chromium.org> wrote:
> > > > > > >
> > > > > > > At present some of the ideas and techniques behind devicetree in U-Boot
> > > > > > > are assumed, implied or unsaid. Add some documentation to cover how
> > > > > > > devicetree is build, how it can be modified and the rules about using
> > > > > > > the various CONFIG_OF_... options.
> > > > > > >
> > > > > > > Signed-off-by: Simon Glass <sjg@chromium.org>
> > > > > > > ---
> > > > > > >
> > > > > > >  doc/develop/index.rst              |   1 +
> > > > > > >  doc/develop/package/devicetree.rst | 315 +++++++++++++++++++++++++++++
> > > > > > >  doc/develop/package/index.rst      |   1 +
> > > > > > >  3 files changed, 317 insertions(+)
> > > > > > >  create mode 100644 doc/develop/package/devicetree.rst
> > > > > > >
> > > > > > > diff --git a/doc/develop/index.rst b/doc/develop/index.rst
> > > > > > > index 83c929babda..d5ad8f9fe53 100644
> > > > > > > --- a/doc/develop/index.rst
> > > > > > > +++ b/doc/develop/index.rst
> > > > > > > @@ -36,6 +36,7 @@ Packaging
> > > > > > >     :maxdepth: 1
> > > > > > >
> > > > > > >     package/index
> > > > > > > +   package/devicetree
> > > > > > >
> > > > > > >  Testing
> > > > > > >  -------
> > > > > > > diff --git a/doc/develop/package/devicetree.rst b/doc/develop/package/devicetree.rst
> > > > > > > new file mode 100644
> > > > > > > index 00000000000..fccbb182f3e
> > > > > > > --- /dev/null
> > > > > > > +++ b/doc/develop/package/devicetree.rst
> > > > > > > @@ -0,0 +1,315 @@
> > > > > > > +.. SPDX-License-Identifier: GPL-2.0+
> > > > > > > +
> > > > > > > +Updating the devicetree
> > > > > > > +=======================
> > > > > > > +
> > > > > > > +U-Boot uses devicetree for runtime configuration and storing required blobs or
> > > > > > > +any other information it needs to operate. It is possible to update the
> > > > > > > +devicetree separately from actually building U-Boot. This provides a good degree
> > > > > > > +of control and flexibility for firmware that uses U-Boot in conjunction with
> > > > > > > +other project.
> > > > > > > +
> > > > > > > +There are many reasons why it is useful to modify the devicetree after building
> > > > > > > +it:
> > > > > > > +
> > > > > > > +- Configuration can be changed, e.g. which UART to use
> > > > > > > +- A serial number can be added
> > > > > > > +- Public keys can be added to allow image verification
> > > > > > > +- Console output can be changed (e.g. to select serial or vidconsole)
> > > > > > > +
> > > > > > > +This section describes how to work with devicetree to accomplish your goals.
> > > > > > > +
> > > > > > > +See also :doc:`../devicetree/control` for a basic summary of the available
> > > > > > > +features.
> > > > > > > +
> > > > > > > +
> > > > > > > +Devicetree source
> > > > > > > +-----------------
> > > > > > > +
> > > > > > > +Every board in U-Boot must include a devicetree sufficient to build and boot
> > > > > > > +that board on suitable hardware (or emulation). This is specified using the
> > > > > > > +`CONFIG DEFAULT_DEVICE_TREE` option.
> > > > > > > +
> > > > > > > +
> > > > > > > +Current situation (August 2021)
> > > > > > > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > > > > > +
> > > > > > > +As an aside, at present U-Boot allows `CONFIG_DEFAULT_DEVICE_TREE` to be empty,
> > > > > > > +e.g. if `CONFIG_OF_BOARD` or `CONFIG_OF_PRIOR_STAGE` are used. This has
> > > > > > > +unfortunately created an enormous amount of confusion and some wasted effort.
> > > > > > > +This was not intended and this bug will be fixed soon. Specifically:
> > > > > > > +
> > > > > > > +- `CONFIG_OF_BOARD` was added in rpi_patch_ for Raspberry Pi, which does have
> > > > > > > +  an in-tree devicetree, but this feature has since been used for boards that
> > > > > > > +  don't
> > > > > > > +- `CONFIG_OF_PRIOR_STAGE` was added in bcm_patch_ as part of a larger Broadcom
> > > > > > > +  change with a tag indicating it only affected one board, so the change in
> > > > > > > +  behaviour was not noticed at the time. It has since been used by RISC-V qemu
> > > > > > > +  boards.
> > > > > > > +
> > > > > > > +Once this bug is fixed, CONFIG_OF_BOARD and CONFIG_OF_PRIOR_STAGE will override
> > > > > > > +(at runtime) the devicetree suppled with U-Boot, but will otherwise use
> > > > > > > +CONFIG_OF_SEPARATE for the in-tree build. So these two will become options,
> > > > > > > +moving out of the 'choice' in `dts/Kconfig`
> > > > > > > +
> > > > > > > +Offending boards are:
> > > > > > > +
> > > > > > > +- bcm7260
> > > > > > > +- bcm7445
> > > > > > > +- qemu_arm64
> > > > > > > +- qemu_arm
> > > > > > > +- qemu-ppce500
> > > > > > > +- qemu-riscv32
> > > > > > > +- qemu-riscv32_smode
> > > > > > > +- qemu-riscv64
> > > > > > > +- qemu-riscv64_smode
> > > > > > > +
> > > > > > > +All of these need to have a devicetree added in-tree. This is targeted to be
> > > > > > > +fixed in the 2022.01 release.
> > > > > >
> > > > > > Do you have some idea of how to support the QEMU case, if not using
> > > > > > CONFIG_OF_PRIOR_STAGE?
> > > > >
> > > > > To be clear, I am not planning to remove this option. It will still work.
> > > > >
> > > > > But I do want to have an in-tree devicetree for all boards, and
> > > > > someone will need to update qemu to support adding U-Boot
> > > > > nodes/properties. It always has an array of options controlling what
> > > > > it presents to BIOS/UEFI, for example, so this should not be too
> > > > > controversial.
> > > >
> > > > I think there is some misunderstanding.
> > > >
> > > > Adding U-Boot nodes/properties is not a problem for QEMU, but the
> > > > thing is that these QEMU targets don't require U-Boot specific
> > > > nodes/properties. It's just that QEMU will generate the DTB on the fly
> > > > based on different command-line options, so the DTB is dynamic and we
> > > > can't hardcode one in the U-Boot tree.
> > >
> > > That's fine, but I do want some sort of sample in the tree, like we
> > > have for qemu-x86 and others. For some reason ARM and RISC-V don't
> > > have one.
> > >
> > > Also, QEMU needs a way to add properties and nodes that are specific
> > > to U-Boot, since at present there is no way at all to pass these
> > > through (/config node, u-boot,dm-xxx tags, etc.).
> >
> > I suppose some of the /config stuff could be nice and that the device
> > tree is indeed the most appropriate way to pass runtime options from
> > QEMU to U-Boot.  But I'd say U-Boot should still work (with reasonable
> > defaults) if no U-Boot specific options are present in the device
> > tree.
> 
> Well I believe it does and actually I think CI currently checks
> this.The config node is certainly optional. But it would not support
> booting signed images, for example, without the public key.

The public key would need to be included in what's passed to us, yes?

-- 
Tom

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Re: [PATCH] doc: Add documentation about devicetree usage

[Tom Rini]

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On Sun, Aug 29, 2021 at 09:43:12PM +0800, Bin Meng wrote:
> Hi Simon,
> 
> On Sun, Aug 29, 2021 at 9:03 PM Simon Glass <sjg@chromium.org> wrote:
> >
> > Hi Mark,
> >
> > On Sun, 29 Aug 2021 at 02:19, Mark Kettenis <mark.kettenis@xs4all.nl> wrote:
> > >
> > > > From: Simon Glass <sjg@chromium.org>
> > > > Date: Sat, 28 Aug 2021 20:07:27 -0600
> > > >
> > > > Hi Bin,
> > > >
> > > > On Sat, 28 Aug 2021 at 19:29, Bin Meng <bmeng.cn@gmail.com> wrote:
> > > > >
> > > > > Hi Simon,
> > > > >
> > > > > On Sun, Aug 29, 2021 at 12:45 AM Simon Glass <sjg@chromium.org> wrote:
> > > > > >
> > > > > > Hi Bin,
> > > > > >
> > > > > > On Sat, 28 Aug 2021 at 07:15, Bin Meng <bmeng.cn@gmail.com> wrote:
> > > > > > >
> > > > > > > Hi Simon,
> > > > > > >
> > > > > > > On Sat, Aug 28, 2021 at 11:23 AM Simon Glass <sjg@chromium.org> wrote:
> > > > > > > >
> > > > > > > > At present some of the ideas and techniques behind devicetree in U-Boot
> > > > > > > > are assumed, implied or unsaid. Add some documentation to cover how
> > > > > > > > devicetree is build, how it can be modified and the rules about using
> > > > > > > > the various CONFIG_OF_... options.
> > > > > > > >
> > > > > > > > Signed-off-by: Simon Glass <sjg@chromium.org>
> > > > > > > > ---
> > > > > > > >
> > > > > > > >  doc/develop/index.rst              |   1 +
> > > > > > > >  doc/develop/package/devicetree.rst | 315 +++++++++++++++++++++++++++++
> > > > > > > >  doc/develop/package/index.rst      |   1 +
> > > > > > > >  3 files changed, 317 insertions(+)
> > > > > > > >  create mode 100644 doc/develop/package/devicetree.rst
> > > > > > > >
> > > > > > > > diff --git a/doc/develop/index.rst b/doc/develop/index.rst
> > > > > > > > index 83c929babda..d5ad8f9fe53 100644
> > > > > > > > --- a/doc/develop/index.rst
> > > > > > > > +++ b/doc/develop/index.rst
> > > > > > > > @@ -36,6 +36,7 @@ Packaging
> > > > > > > >     :maxdepth: 1
> > > > > > > >
> > > > > > > >     package/index
> > > > > > > > +   package/devicetree
> > > > > > > >
> > > > > > > >  Testing
> > > > > > > >  -------
> > > > > > > > diff --git a/doc/develop/package/devicetree.rst b/doc/develop/package/devicetree.rst
> > > > > > > > new file mode 100644
> > > > > > > > index 00000000000..fccbb182f3e
> > > > > > > > --- /dev/null
> > > > > > > > +++ b/doc/develop/package/devicetree.rst
> > > > > > > > @@ -0,0 +1,315 @@
> > > > > > > > +.. SPDX-License-Identifier: GPL-2.0+
> > > > > > > > +
> > > > > > > > +Updating the devicetree
> > > > > > > > +=======================
> > > > > > > > +
> > > > > > > > +U-Boot uses devicetree for runtime configuration and storing required blobs or
> > > > > > > > +any other information it needs to operate. It is possible to update the
> > > > > > > > +devicetree separately from actually building U-Boot. This provides a good degree
> > > > > > > > +of control and flexibility for firmware that uses U-Boot in conjunction with
> > > > > > > > +other project.
> > > > > > > > +
> > > > > > > > +There are many reasons why it is useful to modify the devicetree after building
> > > > > > > > +it:
> > > > > > > > +
> > > > > > > > +- Configuration can be changed, e.g. which UART to use
> > > > > > > > +- A serial number can be added
> > > > > > > > +- Public keys can be added to allow image verification
> > > > > > > > +- Console output can be changed (e.g. to select serial or vidconsole)
> > > > > > > > +
> > > > > > > > +This section describes how to work with devicetree to accomplish your goals.
> > > > > > > > +
> > > > > > > > +See also :doc:`../devicetree/control` for a basic summary of the available
> > > > > > > > +features.
> > > > > > > > +
> > > > > > > > +
> > > > > > > > +Devicetree source
> > > > > > > > +-----------------
> > > > > > > > +
> > > > > > > > +Every board in U-Boot must include a devicetree sufficient to build and boot
> > > > > > > > +that board on suitable hardware (or emulation). This is specified using the
> > > > > > > > +`CONFIG DEFAULT_DEVICE_TREE` option.
> > > > > > > > +
> > > > > > > > +
> > > > > > > > +Current situation (August 2021)
> > > > > > > > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > > > > > > +
> > > > > > > > +As an aside, at present U-Boot allows `CONFIG_DEFAULT_DEVICE_TREE` to be empty,
> > > > > > > > +e.g. if `CONFIG_OF_BOARD` or `CONFIG_OF_PRIOR_STAGE` are used. This has
> > > > > > > > +unfortunately created an enormous amount of confusion and some wasted effort.
> > > > > > > > +This was not intended and this bug will be fixed soon. Specifically:
> > > > > > > > +
> > > > > > > > +- `CONFIG_OF_BOARD` was added in rpi_patch_ for Raspberry Pi, which does have
> > > > > > > > +  an in-tree devicetree, but this feature has since been used for boards that
> > > > > > > > +  don't
> > > > > > > > +- `CONFIG_OF_PRIOR_STAGE` was added in bcm_patch_ as part of a larger Broadcom
> > > > > > > > +  change with a tag indicating it only affected one board, so the change in
> > > > > > > > +  behaviour was not noticed at the time. It has since been used by RISC-V qemu
> > > > > > > > +  boards.
> > > > > > > > +
> > > > > > > > +Once this bug is fixed, CONFIG_OF_BOARD and CONFIG_OF_PRIOR_STAGE will override
> > > > > > > > +(at runtime) the devicetree suppled with U-Boot, but will otherwise use
> > > > > > > > +CONFIG_OF_SEPARATE for the in-tree build. So these two will become options,
> > > > > > > > +moving out of the 'choice' in `dts/Kconfig`
> > > > > > > > +
> > > > > > > > +Offending boards are:
> > > > > > > > +
> > > > > > > > +- bcm7260
> > > > > > > > +- bcm7445
> > > > > > > > +- qemu_arm64
> > > > > > > > +- qemu_arm
> > > > > > > > +- qemu-ppce500
> > > > > > > > +- qemu-riscv32
> > > > > > > > +- qemu-riscv32_smode
> > > > > > > > +- qemu-riscv64
> > > > > > > > +- qemu-riscv64_smode
> > > > > > > > +
> > > > > > > > +All of these need to have a devicetree added in-tree. This is targeted to be
> > > > > > > > +fixed in the 2022.01 release.
> > > > > > >
> > > > > > > Do you have some idea of how to support the QEMU case, if not using
> > > > > > > CONFIG_OF_PRIOR_STAGE?
> > > > > >
> > > > > > To be clear, I am not planning to remove this option. It will still work.
> > > > > >
> > > > > > But I do want to have an in-tree devicetree for all boards, and
> > > > > > someone will need to update qemu to support adding U-Boot
> > > > > > nodes/properties. It always has an array of options controlling what
> > > > > > it presents to BIOS/UEFI, for example, so this should not be too
> > > > > > controversial.
> > > > >
> > > > > I think there is some misunderstanding.
> > > > >
> > > > > Adding U-Boot nodes/properties is not a problem for QEMU, but the
> > > > > thing is that these QEMU targets don't require U-Boot specific
> > > > > nodes/properties. It's just that QEMU will generate the DTB on the fly
> > > > > based on different command-line options, so the DTB is dynamic and we
> > > > > can't hardcode one in the U-Boot tree.
> > > >
> > > > That's fine, but I do want some sort of sample in the tree, like we
> > > > have for qemu-x86 and others. For some reason ARM and RISC-V don't
> > > > have one.
> > > >
> > > > Also, QEMU needs a way to add properties and nodes that are specific
> > > > to U-Boot, since at present there is no way at all to pass these
> > > > through (/config node, u-boot,dm-xxx tags, etc.).
> > >
> > > I suppose some of the /config stuff could be nice and that the device
> > > tree is indeed the most appropriate way to pass runtime options from
> > > QEMU to U-Boot.  But I'd say U-Boot should still work (with reasonable
> > > defaults) if no U-Boot specific options are present in the device
> > > tree.
> >
> > Well I believe it does and actually I think CI currently checks
> > this.The config node is certainly optional. But it would not support
> > booting signed images, for example, without the public key.
> >
> > >
> > > My understanding is that the u-boot,dm-xxx tags are for SPL.  It seems
> > > that for most scenarios having where there is some prior firmware that
> > > passes a device tree, SPL isn't used.  That certainly is the case for
> > > QEMU, Raspberry Pi and my Apple M1 work.
> >
> > Yes that is true and I suppose is how things are able to work at present.
> >
> > But I do see QMU for RISC-V with an SPL boot, although it is only
> > mentioned in the docs, so perhaps it is not in the CI yet. If there
> > are few enough devices and enough memory (and you don't care about
> > boot speed) then the u-boot,dm-xxx tags are not strictly necessary.
> > But then we are using QEMU in a somewhat unrealistic state.
> >
> 
> RISC-V SPL is in CI testing. See qemu_riscv{32,64}_spl targets in the
> u-boot/master and the recent patches for SiFive Unleashed.

The qemu cases are so that we have the SPL flow in CI, right?

-- 
Tom

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Re: [PATCH] doc: Add documentation about devicetree usage

[Bin Meng]

On Sun, Aug 29, 2021 at 10:47 PM Tom Rini <trini@konsulko.com> wrote:
>
> On Sun, Aug 29, 2021 at 09:43:12PM +0800, Bin Meng wrote:
> > Hi Simon,
> >
> > On Sun, Aug 29, 2021 at 9:03 PM Simon Glass <sjg@chromium.org> wrote:
> > >
> > > Hi Mark,
> > >
> > > On Sun, 29 Aug 2021 at 02:19, Mark Kettenis <mark.kettenis@xs4all.nl> wrote:
> > > >
> > > > > From: Simon Glass <sjg@chromium.org>
> > > > > Date: Sat, 28 Aug 2021 20:07:27 -0600
> > > > >
> > > > > Hi Bin,
> > > > >
> > > > > On Sat, 28 Aug 2021 at 19:29, Bin Meng <bmeng.cn@gmail.com> wrote:
> > > > > >
> > > > > > Hi Simon,
> > > > > >
> > > > > > On Sun, Aug 29, 2021 at 12:45 AM Simon Glass <sjg@chromium.org> wrote:
> > > > > > >
> > > > > > > Hi Bin,
> > > > > > >
> > > > > > > On Sat, 28 Aug 2021 at 07:15, Bin Meng <bmeng.cn@gmail.com> wrote:
> > > > > > > >
> > > > > > > > Hi Simon,
> > > > > > > >
> > > > > > > > On Sat, Aug 28, 2021 at 11:23 AM Simon Glass <sjg@chromium.org> wrote:
> > > > > > > > >
> > > > > > > > > At present some of the ideas and techniques behind devicetree in U-Boot
> > > > > > > > > are assumed, implied or unsaid. Add some documentation to cover how
> > > > > > > > > devicetree is build, how it can be modified and the rules about using
> > > > > > > > > the various CONFIG_OF_... options.
> > > > > > > > >
> > > > > > > > > Signed-off-by: Simon Glass <sjg@chromium.org>
> > > > > > > > > ---
> > > > > > > > >
> > > > > > > > >  doc/develop/index.rst              |   1 +
> > > > > > > > >  doc/develop/package/devicetree.rst | 315 +++++++++++++++++++++++++++++
> > > > > > > > >  doc/develop/package/index.rst      |   1 +
> > > > > > > > >  3 files changed, 317 insertions(+)
> > > > > > > > >  create mode 100644 doc/develop/package/devicetree.rst
> > > > > > > > >
> > > > > > > > > diff --git a/doc/develop/index.rst b/doc/develop/index.rst
> > > > > > > > > index 83c929babda..d5ad8f9fe53 100644
> > > > > > > > > --- a/doc/develop/index.rst
> > > > > > > > > +++ b/doc/develop/index.rst
> > > > > > > > > @@ -36,6 +36,7 @@ Packaging
> > > > > > > > >     :maxdepth: 1
> > > > > > > > >
> > > > > > > > >     package/index
> > > > > > > > > +   package/devicetree
> > > > > > > > >
> > > > > > > > >  Testing
> > > > > > > > >  -------
> > > > > > > > > diff --git a/doc/develop/package/devicetree.rst b/doc/develop/package/devicetree.rst
> > > > > > > > > new file mode 100644
> > > > > > > > > index 00000000000..fccbb182f3e
> > > > > > > > > --- /dev/null
> > > > > > > > > +++ b/doc/develop/package/devicetree.rst
> > > > > > > > > @@ -0,0 +1,315 @@
> > > > > > > > > +.. SPDX-License-Identifier: GPL-2.0+
> > > > > > > > > +
> > > > > > > > > +Updating the devicetree
> > > > > > > > > +=======================
> > > > > > > > > +
> > > > > > > > > +U-Boot uses devicetree for runtime configuration and storing required blobs or
> > > > > > > > > +any other information it needs to operate. It is possible to update the
> > > > > > > > > +devicetree separately from actually building U-Boot. This provides a good degree
> > > > > > > > > +of control and flexibility for firmware that uses U-Boot in conjunction with
> > > > > > > > > +other project.
> > > > > > > > > +
> > > > > > > > > +There are many reasons why it is useful to modify the devicetree after building
> > > > > > > > > +it:
> > > > > > > > > +
> > > > > > > > > +- Configuration can be changed, e.g. which UART to use
> > > > > > > > > +- A serial number can be added
> > > > > > > > > +- Public keys can be added to allow image verification
> > > > > > > > > +- Console output can be changed (e.g. to select serial or vidconsole)
> > > > > > > > > +
> > > > > > > > > +This section describes how to work with devicetree to accomplish your goals.
> > > > > > > > > +
> > > > > > > > > +See also :doc:`../devicetree/control` for a basic summary of the available
> > > > > > > > > +features.
> > > > > > > > > +
> > > > > > > > > +
> > > > > > > > > +Devicetree source
> > > > > > > > > +-----------------
> > > > > > > > > +
> > > > > > > > > +Every board in U-Boot must include a devicetree sufficient to build and boot
> > > > > > > > > +that board on suitable hardware (or emulation). This is specified using the
> > > > > > > > > +`CONFIG DEFAULT_DEVICE_TREE` option.
> > > > > > > > > +
> > > > > > > > > +
> > > > > > > > > +Current situation (August 2021)
> > > > > > > > > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > > > > > > > +
> > > > > > > > > +As an aside, at present U-Boot allows `CONFIG_DEFAULT_DEVICE_TREE` to be empty,
> > > > > > > > > +e.g. if `CONFIG_OF_BOARD` or `CONFIG_OF_PRIOR_STAGE` are used. This has
> > > > > > > > > +unfortunately created an enormous amount of confusion and some wasted effort.
> > > > > > > > > +This was not intended and this bug will be fixed soon. Specifically:
> > > > > > > > > +
> > > > > > > > > +- `CONFIG_OF_BOARD` was added in rpi_patch_ for Raspberry Pi, which does have
> > > > > > > > > +  an in-tree devicetree, but this feature has since been used for boards that
> > > > > > > > > +  don't
> > > > > > > > > +- `CONFIG_OF_PRIOR_STAGE` was added in bcm_patch_ as part of a larger Broadcom
> > > > > > > > > +  change with a tag indicating it only affected one board, so the change in
> > > > > > > > > +  behaviour was not noticed at the time. It has since been used by RISC-V qemu
> > > > > > > > > +  boards.
> > > > > > > > > +
> > > > > > > > > +Once this bug is fixed, CONFIG_OF_BOARD and CONFIG_OF_PRIOR_STAGE will override
> > > > > > > > > +(at runtime) the devicetree suppled with U-Boot, but will otherwise use
> > > > > > > > > +CONFIG_OF_SEPARATE for the in-tree build. So these two will become options,
> > > > > > > > > +moving out of the 'choice' in `dts/Kconfig`
> > > > > > > > > +
> > > > > > > > > +Offending boards are:
> > > > > > > > > +
> > > > > > > > > +- bcm7260
> > > > > > > > > +- bcm7445
> > > > > > > > > +- qemu_arm64
> > > > > > > > > +- qemu_arm
> > > > > > > > > +- qemu-ppce500
> > > > > > > > > +- qemu-riscv32
> > > > > > > > > +- qemu-riscv32_smode
> > > > > > > > > +- qemu-riscv64
> > > > > > > > > +- qemu-riscv64_smode
> > > > > > > > > +
> > > > > > > > > +All of these need to have a devicetree added in-tree. This is targeted to be
> > > > > > > > > +fixed in the 2022.01 release.
> > > > > > > >
> > > > > > > > Do you have some idea of how to support the QEMU case, if not using
> > > > > > > > CONFIG_OF_PRIOR_STAGE?
> > > > > > >
> > > > > > > To be clear, I am not planning to remove this option. It will still work.
> > > > > > >
> > > > > > > But I do want to have an in-tree devicetree for all boards, and
> > > > > > > someone will need to update qemu to support adding U-Boot
> > > > > > > nodes/properties. It always has an array of options controlling what
> > > > > > > it presents to BIOS/UEFI, for example, so this should not be too
> > > > > > > controversial.
> > > > > >
> > > > > > I think there is some misunderstanding.
> > > > > >
> > > > > > Adding U-Boot nodes/properties is not a problem for QEMU, but the
> > > > > > thing is that these QEMU targets don't require U-Boot specific
> > > > > > nodes/properties. It's just that QEMU will generate the DTB on the fly
> > > > > > based on different command-line options, so the DTB is dynamic and we
> > > > > > can't hardcode one in the U-Boot tree.
> > > > >
> > > > > That's fine, but I do want some sort of sample in the tree, like we
> > > > > have for qemu-x86 and others. For some reason ARM and RISC-V don't
> > > > > have one.
> > > > >
> > > > > Also, QEMU needs a way to add properties and nodes that are specific
> > > > > to U-Boot, since at present there is no way at all to pass these
> > > > > through (/config node, u-boot,dm-xxx tags, etc.).
> > > >
> > > > I suppose some of the /config stuff could be nice and that the device
> > > > tree is indeed the most appropriate way to pass runtime options from
> > > > QEMU to U-Boot.  But I'd say U-Boot should still work (with reasonable
> > > > defaults) if no U-Boot specific options are present in the device
> > > > tree.
> > >
> > > Well I believe it does and actually I think CI currently checks
> > > this.The config node is certainly optional. But it would not support
> > > booting signed images, for example, without the public key.
> > >
> > > >
> > > > My understanding is that the u-boot,dm-xxx tags are for SPL.  It seems
> > > > that for most scenarios having where there is some prior firmware that
> > > > passes a device tree, SPL isn't used.  That certainly is the case for
> > > > QEMU, Raspberry Pi and my Apple M1 work.
> > >
> > > Yes that is true and I suppose is how things are able to work at present.
> > >
> > > But I do see QMU for RISC-V with an SPL boot, although it is only
> > > mentioned in the docs, so perhaps it is not in the CI yet. If there
> > > are few enough devices and enough memory (and you don't care about
> > > boot speed) then the u-boot,dm-xxx tags are not strictly necessary.
> > > But then we are using QEMU in a somewhat unrealistic state.
> > >
> >
> > RISC-V SPL is in CI testing. See qemu_riscv{32,64}_spl targets in the
> > u-boot/master and the recent patches for SiFive Unleashed.
>
> The qemu cases are so that we have the SPL flow in CI, right?

Yes, for both QEMU-as-QEMU case and QEMU-as-hardware.

Regards,
Bin

Re: [PATCH] doc: Add documentation about devicetree usage

[Simon Glass]

Hi,

On Sun, 29 Aug 2021 at 08:47, Tom Rini <trini@konsulko.com> wrote:
>
> On Sun, Aug 29, 2021 at 09:43:12PM +0800, Bin Meng wrote:
> > Hi Simon,
> >
> > On Sun, Aug 29, 2021 at 9:03 PM Simon Glass <sjg@chromium.org> wrote:
> > >
> > > Hi Mark,
> > >
> > > On Sun, 29 Aug 2021 at 02:19, Mark Kettenis <mark.kettenis@xs4all.nl> wrote:
> > > >
> > > > > From: Simon Glass <sjg@chromium.org>
> > > > > Date: Sat, 28 Aug 2021 20:07:27 -0600
> > > > >
> > > > > Hi Bin,
> > > > >
> > > > > On Sat, 28 Aug 2021 at 19:29, Bin Meng <bmeng.cn@gmail.com> wrote:
> > > > > >
> > > > > > Hi Simon,
> > > > > >
> > > > > > On Sun, Aug 29, 2021 at 12:45 AM Simon Glass <sjg@chromium.org> wrote:
> > > > > > >
> > > > > > > Hi Bin,
> > > > > > >
> > > > > > > On Sat, 28 Aug 2021 at 07:15, Bin Meng <bmeng.cn@gmail.com> wrote:
> > > > > > > >
> > > > > > > > Hi Simon,
> > > > > > > >
> > > > > > > > On Sat, Aug 28, 2021 at 11:23 AM Simon Glass <sjg@chromium.org> wrote:
> > > > > > > > >
> > > > > > > > > At present some of the ideas and techniques behind devicetree in U-Boot
> > > > > > > > > are assumed, implied or unsaid. Add some documentation to cover how
> > > > > > > > > devicetree is build, how it can be modified and the rules about using
> > > > > > > > > the various CONFIG_OF_... options.
> > > > > > > > >
> > > > > > > > > Signed-off-by: Simon Glass <sjg@chromium.org>
> > > > > > > > > ---
> > > > > > > > >
> > > > > > > > >  doc/develop/index.rst              |   1 +
> > > > > > > > >  doc/develop/package/devicetree.rst | 315 +++++++++++++++++++++++++++++
> > > > > > > > >  doc/develop/package/index.rst      |   1 +
> > > > > > > > >  3 files changed, 317 insertions(+)
> > > > > > > > >  create mode 100644 doc/develop/package/devicetree.rst
> > > > > > > > >
> > > > > > > > > diff --git a/doc/develop/index.rst b/doc/develop/index.rst
> > > > > > > > > index 83c929babda..d5ad8f9fe53 100644
> > > > > > > > > --- a/doc/develop/index.rst
> > > > > > > > > +++ b/doc/develop/index.rst
> > > > > > > > > @@ -36,6 +36,7 @@ Packaging
> > > > > > > > >     :maxdepth: 1
> > > > > > > > >
> > > > > > > > >     package/index
> > > > > > > > > +   package/devicetree
> > > > > > > > >
> > > > > > > > >  Testing
> > > > > > > > >  -------
> > > > > > > > > diff --git a/doc/develop/package/devicetree.rst b/doc/develop/package/devicetree.rst
> > > > > > > > > new file mode 100644
> > > > > > > > > index 00000000000..fccbb182f3e
> > > > > > > > > --- /dev/null
> > > > > > > > > +++ b/doc/develop/package/devicetree.rst
> > > > > > > > > @@ -0,0 +1,315 @@
> > > > > > > > > +.. SPDX-License-Identifier: GPL-2.0+
> > > > > > > > > +
> > > > > > > > > +Updating the devicetree
> > > > > > > > > +=======================
> > > > > > > > > +
> > > > > > > > > +U-Boot uses devicetree for runtime configuration and storing required blobs or
> > > > > > > > > +any other information it needs to operate. It is possible to update the
> > > > > > > > > +devicetree separately from actually building U-Boot. This provides a good degree
> > > > > > > > > +of control and flexibility for firmware that uses U-Boot in conjunction with
> > > > > > > > > +other project.
> > > > > > > > > +
> > > > > > > > > +There are many reasons why it is useful to modify the devicetree after building
> > > > > > > > > +it:
> > > > > > > > > +
> > > > > > > > > +- Configuration can be changed, e.g. which UART to use
> > > > > > > > > +- A serial number can be added
> > > > > > > > > +- Public keys can be added to allow image verification
> > > > > > > > > +- Console output can be changed (e.g. to select serial or vidconsole)
> > > > > > > > > +
> > > > > > > > > +This section describes how to work with devicetree to accomplish your goals.
> > > > > > > > > +
> > > > > > > > > +See also :doc:`../devicetree/control` for a basic summary of the available
> > > > > > > > > +features.
> > > > > > > > > +
> > > > > > > > > +
> > > > > > > > > +Devicetree source
> > > > > > > > > +-----------------
> > > > > > > > > +
> > > > > > > > > +Every board in U-Boot must include a devicetree sufficient to build and boot
> > > > > > > > > +that board on suitable hardware (or emulation). This is specified using the
> > > > > > > > > +`CONFIG DEFAULT_DEVICE_TREE` option.
> > > > > > > > > +
> > > > > > > > > +
> > > > > > > > > +Current situation (August 2021)
> > > > > > > > > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > > > > > > > +
> > > > > > > > > +As an aside, at present U-Boot allows `CONFIG_DEFAULT_DEVICE_TREE` to be empty,
> > > > > > > > > +e.g. if `CONFIG_OF_BOARD` or `CONFIG_OF_PRIOR_STAGE` are used. This has
> > > > > > > > > +unfortunately created an enormous amount of confusion and some wasted effort.
> > > > > > > > > +This was not intended and this bug will be fixed soon. Specifically:
> > > > > > > > > +
> > > > > > > > > +- `CONFIG_OF_BOARD` was added in rpi_patch_ for Raspberry Pi, which does have
> > > > > > > > > +  an in-tree devicetree, but this feature has since been used for boards that
> > > > > > > > > +  don't
> > > > > > > > > +- `CONFIG_OF_PRIOR_STAGE` was added in bcm_patch_ as part of a larger Broadcom
> > > > > > > > > +  change with a tag indicating it only affected one board, so the change in
> > > > > > > > > +  behaviour was not noticed at the time. It has since been used by RISC-V qemu
> > > > > > > > > +  boards.
> > > > > > > > > +
> > > > > > > > > +Once this bug is fixed, CONFIG_OF_BOARD and CONFIG_OF_PRIOR_STAGE will override
> > > > > > > > > +(at runtime) the devicetree suppled with U-Boot, but will otherwise use
> > > > > > > > > +CONFIG_OF_SEPARATE for the in-tree build. So these two will become options,
> > > > > > > > > +moving out of the 'choice' in `dts/Kconfig`
> > > > > > > > > +
> > > > > > > > > +Offending boards are:
> > > > > > > > > +
> > > > > > > > > +- bcm7260
> > > > > > > > > +- bcm7445
> > > > > > > > > +- qemu_arm64
> > > > > > > > > +- qemu_arm
> > > > > > > > > +- qemu-ppce500
> > > > > > > > > +- qemu-riscv32
> > > > > > > > > +- qemu-riscv32_smode
> > > > > > > > > +- qemu-riscv64
> > > > > > > > > +- qemu-riscv64_smode
> > > > > > > > > +
> > > > > > > > > +All of these need to have a devicetree added in-tree. This is targeted to be
> > > > > > > > > +fixed in the 2022.01 release.
> > > > > > > >
> > > > > > > > Do you have some idea of how to support the QEMU case, if not using
> > > > > > > > CONFIG_OF_PRIOR_STAGE?
> > > > > > >
> > > > > > > To be clear, I am not planning to remove this option. It will still work.
> > > > > > >
> > > > > > > But I do want to have an in-tree devicetree for all boards, and
> > > > > > > someone will need to update qemu to support adding U-Boot
> > > > > > > nodes/properties. It always has an array of options controlling what
> > > > > > > it presents to BIOS/UEFI, for example, so this should not be too
> > > > > > > controversial.
> > > > > >
> > > > > > I think there is some misunderstanding.
> > > > > >
> > > > > > Adding U-Boot nodes/properties is not a problem for QEMU, but the
> > > > > > thing is that these QEMU targets don't require U-Boot specific
> > > > > > nodes/properties. It's just that QEMU will generate the DTB on the fly
> > > > > > based on different command-line options, so the DTB is dynamic and we
> > > > > > can't hardcode one in the U-Boot tree.
> > > > >
> > > > > That's fine, but I do want some sort of sample in the tree, like we
> > > > > have for qemu-x86 and others. For some reason ARM and RISC-V don't
> > > > > have one.
> > > > >
> > > > > Also, QEMU needs a way to add properties and nodes that are specific
> > > > > to U-Boot, since at present there is no way at all to pass these
> > > > > through (/config node, u-boot,dm-xxx tags, etc.).
> > > >
> > > > I suppose some of the /config stuff could be nice and that the device
> > > > tree is indeed the most appropriate way to pass runtime options from
> > > > QEMU to U-Boot.  But I'd say U-Boot should still work (with reasonable
> > > > defaults) if no U-Boot specific options are present in the device
> > > > tree.
> > >
> > > Well I believe it does and actually I think CI currently checks
> > > this.The config node is certainly optional. But it would not support
> > > booting signed images, for example, without the public key.
> > >
> > > >
> > > > My understanding is that the u-boot,dm-xxx tags are for SPL.  It seems
> > > > that for most scenarios having where there is some prior firmware that
> > > > passes a device tree, SPL isn't used.  That certainly is the case for
> > > > QEMU, Raspberry Pi and my Apple M1 work.
> > >
> > > Yes that is true and I suppose is how things are able to work at present.
> > >
> > > But I do see QMU for RISC-V with an SPL boot, although it is only
> > > mentioned in the docs, so perhaps it is not in the CI yet. If there
> > > are few enough devices and enough memory (and you don't care about
> > > boot speed) then the u-boot,dm-xxx tags are not strictly necessary.
> > > But then we are using QEMU in a somewhat unrealistic state.
> > >
> >
> > RISC-V SPL is in CI testing. See qemu_riscv{32,64}_spl targets in the
> > u-boot/master and the recent patches for SiFive Unleashed.
>
> The qemu cases are so that we have the SPL flow in CI, right?

My guess is that we need to add some u-boot,dm... tags to test this properly.

Regards,
Simon

Re: [PATCH] doc: Add documentation about devicetree usage

[Simon Glass]

Hi Tom,

On Sun, 29 Aug 2021 at 08:46, Tom Rini <trini@konsulko.com> wrote:
>
> On Sun, Aug 29, 2021 at 07:03:14AM -0600, Simon Glass wrote:
> > Hi Mark,
> >
> > On Sun, 29 Aug 2021 at 02:19, Mark Kettenis <mark.kettenis@xs4all.nl> wrote:
> > >
> > > > From: Simon Glass <sjg@chromium.org>
> > > > Date: Sat, 28 Aug 2021 20:07:27 -0600
> > > >
> > > > Hi Bin,
> > > >
> > > > On Sat, 28 Aug 2021 at 19:29, Bin Meng <bmeng.cn@gmail.com> wrote:
> > > > >
> > > > > Hi Simon,
> > > > >
> > > > > On Sun, Aug 29, 2021 at 12:45 AM Simon Glass <sjg@chromium.org> wrote:
> > > > > >
> > > > > > Hi Bin,
> > > > > >
> > > > > > On Sat, 28 Aug 2021 at 07:15, Bin Meng <bmeng.cn@gmail.com> wrote:
> > > > > > >
> > > > > > > Hi Simon,
> > > > > > >
> > > > > > > On Sat, Aug 28, 2021 at 11:23 AM Simon Glass <sjg@chromium.org> wrote:
> > > > > > > >
> > > > > > > > At present some of the ideas and techniques behind devicetree in U-Boot
> > > > > > > > are assumed, implied or unsaid. Add some documentation to cover how
> > > > > > > > devicetree is build, how it can be modified and the rules about using
> > > > > > > > the various CONFIG_OF_... options.
> > > > > > > >
> > > > > > > > Signed-off-by: Simon Glass <sjg@chromium.org>
> > > > > > > > ---
> > > > > > > >
> > > > > > > >  doc/develop/index.rst              |   1 +
> > > > > > > >  doc/develop/package/devicetree.rst | 315 +++++++++++++++++++++++++++++
> > > > > > > >  doc/develop/package/index.rst      |   1 +
> > > > > > > >  3 files changed, 317 insertions(+)
> > > > > > > >  create mode 100644 doc/develop/package/devicetree.rst
> > > > > > > >
> > > > > > > > diff --git a/doc/develop/index.rst b/doc/develop/index.rst
> > > > > > > > index 83c929babda..d5ad8f9fe53 100644
> > > > > > > > --- a/doc/develop/index.rst
> > > > > > > > +++ b/doc/develop/index.rst
> > > > > > > > @@ -36,6 +36,7 @@ Packaging
> > > > > > > >     :maxdepth: 1
> > > > > > > >
> > > > > > > >     package/index
> > > > > > > > +   package/devicetree
> > > > > > > >
> > > > > > > >  Testing
> > > > > > > >  -------
> > > > > > > > diff --git a/doc/develop/package/devicetree.rst b/doc/develop/package/devicetree.rst
> > > > > > > > new file mode 100644
> > > > > > > > index 00000000000..fccbb182f3e
> > > > > > > > --- /dev/null
> > > > > > > > +++ b/doc/develop/package/devicetree.rst
> > > > > > > > @@ -0,0 +1,315 @@
> > > > > > > > +.. SPDX-License-Identifier: GPL-2.0+
> > > > > > > > +
> > > > > > > > +Updating the devicetree
> > > > > > > > +=======================
> > > > > > > > +
> > > > > > > > +U-Boot uses devicetree for runtime configuration and storing required blobs or
> > > > > > > > +any other information it needs to operate. It is possible to update the
> > > > > > > > +devicetree separately from actually building U-Boot. This provides a good degree
> > > > > > > > +of control and flexibility for firmware that uses U-Boot in conjunction with
> > > > > > > > +other project.
> > > > > > > > +
> > > > > > > > +There are many reasons why it is useful to modify the devicetree after building
> > > > > > > > +it:
> > > > > > > > +
> > > > > > > > +- Configuration can be changed, e.g. which UART to use
> > > > > > > > +- A serial number can be added
> > > > > > > > +- Public keys can be added to allow image verification
> > > > > > > > +- Console output can be changed (e.g. to select serial or vidconsole)
> > > > > > > > +
> > > > > > > > +This section describes how to work with devicetree to accomplish your goals.
> > > > > > > > +
> > > > > > > > +See also :doc:`../devicetree/control` for a basic summary of the available
> > > > > > > > +features.
> > > > > > > > +
> > > > > > > > +
> > > > > > > > +Devicetree source
> > > > > > > > +-----------------
> > > > > > > > +
> > > > > > > > +Every board in U-Boot must include a devicetree sufficient to build and boot
> > > > > > > > +that board on suitable hardware (or emulation). This is specified using the
> > > > > > > > +`CONFIG DEFAULT_DEVICE_TREE` option.
> > > > > > > > +
> > > > > > > > +
> > > > > > > > +Current situation (August 2021)
> > > > > > > > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > > > > > > +
> > > > > > > > +As an aside, at present U-Boot allows `CONFIG_DEFAULT_DEVICE_TREE` to be empty,
> > > > > > > > +e.g. if `CONFIG_OF_BOARD` or `CONFIG_OF_PRIOR_STAGE` are used. This has
> > > > > > > > +unfortunately created an enormous amount of confusion and some wasted effort.
> > > > > > > > +This was not intended and this bug will be fixed soon. Specifically:
> > > > > > > > +
> > > > > > > > +- `CONFIG_OF_BOARD` was added in rpi_patch_ for Raspberry Pi, which does have
> > > > > > > > +  an in-tree devicetree, but this feature has since been used for boards that
> > > > > > > > +  don't
> > > > > > > > +- `CONFIG_OF_PRIOR_STAGE` was added in bcm_patch_ as part of a larger Broadcom
> > > > > > > > +  change with a tag indicating it only affected one board, so the change in
> > > > > > > > +  behaviour was not noticed at the time. It has since been used by RISC-V qemu
> > > > > > > > +  boards.
> > > > > > > > +
> > > > > > > > +Once this bug is fixed, CONFIG_OF_BOARD and CONFIG_OF_PRIOR_STAGE will override
> > > > > > > > +(at runtime) the devicetree suppled with U-Boot, but will otherwise use
> > > > > > > > +CONFIG_OF_SEPARATE for the in-tree build. So these two will become options,
> > > > > > > > +moving out of the 'choice' in `dts/Kconfig`
> > > > > > > > +
> > > > > > > > +Offending boards are:
> > > > > > > > +
> > > > > > > > +- bcm7260
> > > > > > > > +- bcm7445
> > > > > > > > +- qemu_arm64
> > > > > > > > +- qemu_arm
> > > > > > > > +- qemu-ppce500
> > > > > > > > +- qemu-riscv32
> > > > > > > > +- qemu-riscv32_smode
> > > > > > > > +- qemu-riscv64
> > > > > > > > +- qemu-riscv64_smode
> > > > > > > > +
> > > > > > > > +All of these need to have a devicetree added in-tree. This is targeted to be
> > > > > > > > +fixed in the 2022.01 release.
> > > > > > >
> > > > > > > Do you have some idea of how to support the QEMU case, if not using
> > > > > > > CONFIG_OF_PRIOR_STAGE?
> > > > > >
> > > > > > To be clear, I am not planning to remove this option. It will still work.
> > > > > >
> > > > > > But I do want to have an in-tree devicetree for all boards, and
> > > > > > someone will need to update qemu to support adding U-Boot
> > > > > > nodes/properties. It always has an array of options controlling what
> > > > > > it presents to BIOS/UEFI, for example, so this should not be too
> > > > > > controversial.
> > > > >
> > > > > I think there is some misunderstanding.
> > > > >
> > > > > Adding U-Boot nodes/properties is not a problem for QEMU, but the
> > > > > thing is that these QEMU targets don't require U-Boot specific
> > > > > nodes/properties. It's just that QEMU will generate the DTB on the fly
> > > > > based on different command-line options, so the DTB is dynamic and we
> > > > > can't hardcode one in the U-Boot tree.
> > > >
> > > > That's fine, but I do want some sort of sample in the tree, like we
> > > > have for qemu-x86 and others. For some reason ARM and RISC-V don't
> > > > have one.
> > > >
> > > > Also, QEMU needs a way to add properties and nodes that are specific
> > > > to U-Boot, since at present there is no way at all to pass these
> > > > through (/config node, u-boot,dm-xxx tags, etc.).
> > >
> > > I suppose some of the /config stuff could be nice and that the device
> > > tree is indeed the most appropriate way to pass runtime options from
> > > QEMU to U-Boot.  But I'd say U-Boot should still work (with reasonable
> > > defaults) if no U-Boot specific options are present in the device
> > > tree.
> >
> > Well I believe it does and actually I think CI currently checks
> > this.The config node is certainly optional. But it would not support
> > booting signed images, for example, without the public key.
>
> The public key would need to be included in what's passed to us, yes?
>

Yes, I suggest adding a -dtsi flag or similar, to provide a DT to
merge with the generated one. Then we could add a vboot test using
qemu, for example, in addition to the sandbox ones.

Regards,
Simon