[U-Boot] [RFC PATCH v2 3/6] fdt: Add support for a separate device tree (CONFIG_OF_SEPARATE)

[Simon Glass <sjg@chromium.org>]

Hi Grant,

On Wed, Sep 14, 2011 at 9:48 AM, Grant Likely <grant.likely@secretlab.ca> wrote:
> On Mon, Sep 12, 2011 at 03:04:24PM -0700, Simon Glass wrote:
>> This adds support for an FDT to be build as a separate binary file called
>> u-boot.dtb. This can be concatenated with the U-Boot binary to provide a
>> device tree located at run-time by U-Boot.
>
> Hahaha, I should the entire thread of patches before commenting. ?I
> strongly feel that this should be the only method and that
> CONFIG_OF_EMBED should be dropped.

:-)

Please see my comments in the other thread.

Regards,
Simon

>
>>
>> Signed-off-by: Simon Glass <sjg@chromium.org>
>> ---
>> ?.gitignore ? ? ? ? ? ? | ? ?1 +
>> ?Makefile ? ? ? ? ? ? ? | ? ?5 ++
>> ?README ? ? ? ? ? ? ? ? | ? 11 +++-
>> ?doc/README.fdt-control | ?168 ++++++++++++++++++++++++++++++++++++++++++++++++
>> ?4 files changed, 183 insertions(+), 2 deletions(-)
>> ?create mode 100644 doc/README.fdt-control
>>
>> diff --git a/.gitignore b/.gitignore
>> index dbf545f..c4ebd34 100644
>> --- a/.gitignore
>> +++ b/.gitignore
>> @@ -34,6 +34,7 @@
>> ?/u-boot.dis
>> ?/u-boot.lds
>> ?/u-boot.ubl
>> +/u-boot.dtb
>>
>> ?#
>> ?# Generated files
>> diff --git a/Makefile b/Makefile
>> index 658a622..d73efa1 100644
>> --- a/Makefile
>> +++ b/Makefile
>> @@ -352,9 +352,14 @@ ALL-$(CONFIG_ONENAND_U_BOOT) += $(obj)u-boot-onenand.bin
>> ?ONENAND_BIN ?= $(obj)onenand_ipl/onenand-ipl-2k.bin
>> ?ALL-$(CONFIG_MMC_U_BOOT) += $(obj)mmc_spl/u-boot-mmc-spl.bin
>> ?ALL-$(CONFIG_SPL) += $(obj)spl/u-boot-spl.bin
>> +ALL-$(CONFIG_OF_SEPARATE) += $(obj)u-boot.dtb
>>
>> ?all: ? ? ? ? $(ALL-y)
>>
>> +$(obj)u-boot.dtb: ? ?$(obj)u-boot
>> + ? ? ? ? ? ? $(MAKE) -C dts binary
>> + ? ? ? ? ? ? mv $(obj)dts/dt.dtb $@
>> +
>> ?$(obj)u-boot.hex: ? ?$(obj)u-boot
>> ? ? ? ? ? ? ? $(OBJCOPY) ${OBJCFLAGS} -O ihex $< $@
>>
>> diff --git a/README b/README
>> index 5a2f060..0b8f338 100644
>> --- a/README
>> +++ b/README
>> @@ -803,8 +803,8 @@ The following options need to be configured:
>> ? ? ? ? ? ? ? experimental and only available on a few boards. The device
>> ? ? ? ? ? ? ? tree is available in the global data as gd->blob.
>>
>> - ? ? ? ? ? ? U-Boot needs to get its device tree from somewhere. At present
>> - ? ? ? ? ? ? the only way is to embed it in the image with CONFIG_OF_EMBED.
>> + ? ? ? ? ? ? U-Boot needs to get its device tree from somewhere. This can
>> + ? ? ? ? ? ? be done using one of the two options below:
>>
>> ? ? ? ? ? ? ? CONFIG_OF_EMBED
>> ? ? ? ? ? ? ? If this variable is defined, U-Boot will embed a device tree
>> @@ -813,6 +813,13 @@ The following options need to be configured:
>> ? ? ? ? ? ? ? is then picked up in board_init_f() and made available through
>> ? ? ? ? ? ? ? the global data structure as gd->blob.
>>
>> + ? ? ? ? ? ? CONFIG_OF_SEPARATE
>> + ? ? ? ? ? ? If this variable is defined, U-Boot will build a device tree
>> + ? ? ? ? ? ? binary. It will be called u-boot.dtb. Architecture-specific
>> + ? ? ? ? ? ? code will locate it at run-time. Generally this works by:
>> +
>> + ? ? ? ? ? ? ? ? ? ? cat u-boot.bin u-boot.dtb >image.bin
>> +
>> ?- Watchdog:
>> ? ? ? ? ? ? ? CONFIG_WATCHDOG
>> ? ? ? ? ? ? ? If this variable is defined, it enables watchdog
>> diff --git a/doc/README.fdt-control b/doc/README.fdt-control
>> new file mode 100644
>> index 0000000..dfc8f06
>> --- /dev/null
>> +++ b/doc/README.fdt-control
>> @@ -0,0 +1,168 @@
>> +#
>> +# Copyright (c) 2011 The Chromium OS Authors.
>> +#
>> +# See file CREDITS for list of people who contributed to this
>> +# project.
>> +#
>> +# This program is free software; you can redistribute it and/or
>> +# modify it under the terms of the GNU General Public License as
>> +# published by the Free Software Foundatio; either version 2 of
>> +# the License, or (at your option) any later version.
>> +#
>> +# This program is distributed in the hope that it will be useful,
>> +# but WITHOUT ANY WARRANTY; without even the implied warranty of
>> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. ? ? ? See the
>> +# GNU General Public License for more details.
>> +#
>> +# You should have received a copy of the GNU General Public License
>> +# along with this program; if not, write to the Free Software
>> +# Foundation, Inc., 59 Temple Place, Suite 330, Boston,
>> +# MA 02111-1307 USA
>> +#
>> +
>> +Device Tree Control in U-Boot
>> +=============================
>> +
>> +This feature provides for run-time configuration of U-Boot via a flat
>> +device tree (fdt). U-Boot configuration has traditionally been done
>> +using CONFIG options in the board config file. This feature aims to
>> +make it possible for a single U-Boot binary to support multiple boards,
>> +with the exact configuration of each board controlled by a flat device
>> +tree (fdt). This is the approach recently taken by the ARM Linux kernel
>> +and has been used by PowerPC for some time.
>> +
>> +The fdt is a convenient vehicle for implementing run-time configuration
>> +for three reasons. Firstly it is easy to use, being a simple text file.
>> +It is extensible since it consists of nodes and properties in a nice
>> +hierarchical format.
>> +
>> +Finally, there is already excellent infrastructure for the fdt: a
>> +compiler checks the text file and converts it to a compact binary
>> +format, and a library is already available in U-Boot (libfdt) for
>> +handling this format.
>> +
>> +The dts directory contains a Makefile for building the device tree blob
>> +and embedding it in your U-Boot image. This is useful since it allows
>> +U-Boot to configure itself according to what it finds there. If you have
>> +a number of similar boards with different peripherals, you can describe
>> +the features of each board in the device tree file, and have a single
>> +generic source base.
>> +
>> +To enable this feature, add CONFIG_OF_CONTROL to your board config file.
>> +
>> +
>> +What is a Flat Device Tree?
>> +---------------------------
>> +
>> +An fdt can be specified in source format as a text file. To read about
>> +the fdt syntax, take a look at the specification here:
>> +
>> +https://www.power.org/resources/downloads/Power_ePAPR_APPROVED_v1.0.pdf
>> +
>> +You also might find this section of the Linux kernel documentation
>> +useful: (access this in the Linux kernel source code)
>> +
>> + ? ? Documentation/devicetree/booting-without-of.txt
>> +
>> +There is also a mailing list:
>> +
>> + ? ? http://lists.ozlabs.org/listinfo/devicetree-discuss
>> +
>> +In case you are wondering, OF stands for Open Firmware.
>> +
>> +
>> +Tools
>> +-----
>> +
>> +To use this feature you will need to get the device tree compiler here:
>> +
>> + ? ? git://jdl.com/software/dtc.git
>> +
>> +For example:
>> +
>> + ? ? $ git clone git://jdl.com/software/dtc.git
>> + ? ? $ cd dtc
>> + ? ? $ make
>> + ? ? $ sudo make install
>> +
>> +Then run the compiler (your version will vary):
>> +
>> + ? ? $ dtc -v
>> + ? ? Version: DTC 1.2.0-g2cb4b51f
>> + ? ? $ make tests
>> + ? ? $ cd tests
>> + ? ? $ ./run_tests.sh
>> + ? ? ********** TEST SUMMARY
>> + ? ? * ? ? Total testcases: ?1371
>> + ? ? * ? ? ? ? ? ? ? ?PASS: ?1371
>> + ? ? * ? ? ? ? ? ? ? ?FAIL: ?0
>> + ? ? * ? Bad configuration: ?0
>> + ? ? * Strange test result: ?0
>> +
>> +You will also find a useful ftdump utility for decoding a binary file.
>> +
>> +
>> +Where do I get an fdt file for my board?
>> +----------------------------------------
>> +
>> +You may find that the Linux kernel has a suitable file. Look in the
>> +kernel source in arch/<arch>/boot/dts.
>> +
>> +If not you might find other boards with suitable files that you can
>> +modify to your needs. Look in the board directories for files with a
>> +.dts extension.
>> +
>> +Failing that, you could write one from scratch yourself!
>> +
>> +
>> +Configuration
>> +-------------
>> +
>> +Use:
>> +
>> +#define CONFIG_DEFAULT_DEVICE_TREE ? "<name>"
>> +
>> +to set the filename of the device tree source. Then put your device tree
>> +file into
>> +
>> + ? ? board/<vendor>/<board>/<name>.dts
>> +
>> +If CONFIG_OF_EMBED is defined, then it will be picked up and built into
>> +the U-Boot image (including u-boot.bin).
>> +
>> +If CONFIG_OF_SEPARATE is defined, then it will be built and placed in
>> +a u-boot.dtb file alongside u-boot.bin. A common approach is then to
>> +join the two:
>> +
>> + ? ? cat u-boot.bin u-boot.dtb >image.bin
>> +
>> +and then flash image.bin onto your board.
>> +
>> +You cannot use both of these options at the same time.
>> +
>> +
>> +Limitations
>> +-----------
>> +
>> +U-Boot is designed to build with a single architecture type and CPU
>> +type. So for example it is not possible to build a single ARM binary
>> +which runs on your AT91 and OMAP boards, relying on an fdt to configure
>> +the various features. This is because you must select one of
>> +the CPU families within arch/arm/cpu/arm926ejs (omap or at91) at build
>> +time. Similarly you cannot build for multiple cpu types or
>> +architectures.
>> +
>> +That said the complexity reduction by using fdt to support variants of
>> +boards which use the same SOC / CPU can be substantial.
>> +
>> +It is important to understand that the fdt only selects options
>> +available in the platform / drivers. It cannot add new drivers (yet). So
>> +you must still have the CONFIG option to enable the driver. For example,
>> +you need to define CONFIG_SYS_NS16550 to bring in the NS16550 driver,
>> +but can use the fdt to specific the UART clock, peripheral address, etc.
>> +In very broad terms, the CONFIG options in general control *what* driver
>> +files are pulled in, and the fdt controls *how* those files work.
>> +
>> +--
>> +Simon Glass <sjg@chromium.org>
>> +1-Sep-11
>> --
>> 1.7.3.1
>>
>