[PATCH 0/5] mtd: core: OTP nvmem provider support

[PATCH 0/5] mtd: core: OTP nvmem provider support

[Michael Walle]

The goal is to fetch a (base) MAC address from the OTP region of a SPI NOR
flash.

This is the first part, where I try to add the nvmem provider support to
the MTD core.

I'm not sure about the device tree bindings. Consider the following two
variants:

(1)
    flash@0 {
        ..

        otp {
            compatible = "mtd-user-otp";
            #address-cells = <1>;
            #size-cells = <1>;

            serial-number@0 {
                reg = <0x0 0x8>;
            };
        };
    };

(2)
    flash@0 {
        ..

        otp {
            compatible = "mtd-user-otp";
            #address-cells = <1>;
            #size-cells = <1>;

			some-useful-name {
                compatible = "nvmem-cells";

                serial-number@0 {
                    reg = <0x0 0x8>;
                };
			};
        };
    };

Both bindings use a subnode "opt[-N]". We cannot have the nvmem cells as
children to the flash node because of the legacy partition binding.

(1) seems to be the form which is used almost everywhere in the kernel.
That is, the nvmem cells are just children of the parent node.

(2) seem to be more natural, because there might also be other properties
inside the otp subnode and might be more future-proof.

At the moment this patch implements (1).

Michael Walle (5):
  nvmem: core: allow specifying of_node
  dt-bindings: mtd: add YAML schema for the generic MTD bindings
  dt-bindings: mtd: add OTP bindings
  dt-bindings: mtd: spi-nor: add otp property
  mtd: core: add OTP nvmem provider support

 .../devicetree/bindings/mtd/common.txt        |  16 +-
 .../bindings/mtd/jedec,spi-nor.yaml           |   6 +
 .../devicetree/bindings/mtd/mtd.yaml          |  89 +++++++++++
 drivers/mtd/mtdcore.c                         | 149 ++++++++++++++++++
 drivers/nvmem/core.c                          |   4 +-
 include/linux/mtd/mtd.h                       |   2 +
 include/linux/nvmem-provider.h                |   2 +
 7 files changed, 252 insertions(+), 16 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/mtd/mtd.yaml

-- 
2.20.1


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[PATCH 1/5] nvmem: core: allow specifying of_node

[Michael Walle]

Until now, the of_node of the parent device is used. Some devices
provide more than just the nvmem provider. To avoid name space clashes,
add a way to allow specifying the nvmem cells in subnodes. Consider the
following example:

    flash@0 {
        compatible = "jedec,spi-nor";

        partitions {
            compatible = "fixed-partitions";
            #address-cells = <1>;
            #size-cells = <1>;

            partition@0 {
                reg = <0x000000 0x010000>;
            };
	};

        otp {
            compatible = "mtd-user-otp";
            #address-cells = <1>;
            #size-cells = <1>;

            serial-number@0 {
                reg = <0x0 0x8>;
            };
        };
    };

There the nvmem provider might be the MTD partition or the OTP region of
the flash.

Add a new config->of_node parameter, which if set, will be used instead
of the parent's of_node.

Signed-off-by: Michael Walle <michael@walle.cc>
Acked-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
---
Changes since RFC:
 - none

 drivers/nvmem/core.c           | 4 +++-
 include/linux/nvmem-provider.h | 2 ++
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
index bca671ff4e54..62d363a399d3 100644
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -789,7 +789,9 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
 	nvmem->reg_write = config->reg_write;
 	nvmem->keepout = config->keepout;
 	nvmem->nkeepout = config->nkeepout;
-	if (!config->no_of_node)
+	if (config->of_node)
+		nvmem->dev.of_node = config->of_node;
+	else if (!config->no_of_node)
 		nvmem->dev.of_node = config->dev->of_node;
 
 	switch (config->id) {
diff --git a/include/linux/nvmem-provider.h b/include/linux/nvmem-provider.h
index e162b757b6d5..471cb7b9e896 100644
--- a/include/linux/nvmem-provider.h
+++ b/include/linux/nvmem-provider.h
@@ -57,6 +57,7 @@ struct nvmem_keepout {
  * @type:	Type of the nvmem storage
  * @read_only:	Device is read-only.
  * @root_only:	Device is accessibly to root only.
+ * @of_node:	If given, this will be used instead of the parent's of_node.
  * @no_of_node:	Device should not use the parent's of_node even if it's !NULL.
  * @reg_read:	Callback to read data.
  * @reg_write:	Callback to write data.
@@ -86,6 +87,7 @@ struct nvmem_config {
 	enum nvmem_type		type;
 	bool			read_only;
 	bool			root_only;
+	struct device_node	*of_node;
 	bool			no_of_node;
 	nvmem_reg_read_t	reg_read;
 	nvmem_reg_write_t	reg_write;
-- 
2.20.1


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[PATCH 2/5] dt-bindings: mtd: add YAML schema for the generic MTD bindings

[Michael Walle]

Convert MTD's common.txt to mtd.yaml.

Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Rob Herring <robh@kernel.org>
---
Changes since RFC:
 - use real device compatibles

 .../devicetree/bindings/mtd/common.txt        | 16 +-------
 .../devicetree/bindings/mtd/mtd.yaml          | 39 +++++++++++++++++++
 2 files changed, 40 insertions(+), 15 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/mtd/mtd.yaml

diff --git a/Documentation/devicetree/bindings/mtd/common.txt b/Documentation/devicetree/bindings/mtd/common.txt
index fc068b923d7a..ae16f9ea8606 100644
--- a/Documentation/devicetree/bindings/mtd/common.txt
+++ b/Documentation/devicetree/bindings/mtd/common.txt
@@ -1,15 +1 @@
-* Common properties of all MTD devices
-
-Optional properties:
-- label: user-defined MTD device name. Can be used to assign user
-  friendly names to MTD devices (instead of the flash model or flash
-  controller based name) in order to ease flash device identification
-  and/or describe what they are used for.
-
-Example:
-
-	flash@0 {
-		label = "System-firmware";
-
-		/* flash type specific properties */
-	};
+This file has been moved to mtd.yaml.
diff --git a/Documentation/devicetree/bindings/mtd/mtd.yaml b/Documentation/devicetree/bindings/mtd/mtd.yaml
new file mode 100644
index 000000000000..086b0ecd1604
--- /dev/null
+++ b/Documentation/devicetree/bindings/mtd/mtd.yaml
@@ -0,0 +1,39 @@
+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/mtd/mtd.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: MTD (Memory Technology Device) Device Tree Bindings
+
+maintainers:
+  - Miquel Raynal <miquel.raynal@bootlin.com>
+  - Richard Weinberger <richard@nod.at>
+
+properties:
+  $nodename:
+    pattern: "^flash(@.*)?$"
+
+  label:
+    description:
+      User-defined MTD device name. Can be used to assign user friendly
+      names to MTD devices (instead of the flash model or flash controller
+      based name) in order to ease flash device identification and/or
+      describe what they are used for.
+
+additionalProperties: true
+
+examples:
+  - |
+    spi {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        flash@0 {
+            reg = <0>;
+            compatible = "jedec,spi-nor";
+            label = "System-firmware";
+        };
+    };
+
+...
-- 
2.20.1


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[PATCH 3/5] dt-bindings: mtd: add OTP bindings

[Michael Walle]

Flash devices can have one-time-programmable regions. Add a nvmem
binding so they can be used as a nvmem provider.

Signed-off-by: Michael Walle <michael@walle.cc>
---
Changes since RFC:
 - added missing "$"
 - dropped first example
 - use real device compatibles

   Please note, that this will lead to an error without patch 4/5, which
   introduces that property for the jedec,spi-nor. Should I keep it
   seperate or should I squash that patch into this one?

 .../devicetree/bindings/mtd/mtd.yaml          | 50 +++++++++++++++++++
 1 file changed, 50 insertions(+)

diff --git a/Documentation/devicetree/bindings/mtd/mtd.yaml b/Documentation/devicetree/bindings/mtd/mtd.yaml
index 086b0ecd1604..dd43fb8b4fd1 100644
--- a/Documentation/devicetree/bindings/mtd/mtd.yaml
+++ b/Documentation/devicetree/bindings/mtd/mtd.yaml
@@ -21,6 +21,25 @@ properties:
       based name) in order to ease flash device identification and/or
       describe what they are used for.
 
+patternProperties:
+  "^otp(-[0-9]+)?$":
+    type: object
+    $ref: ../nvmem/nvmem.yaml#
+
+    description: |
+      An OTP memory region. Some flashes provide a one-time-programmable
+      memory whose content can either be programmed by a user or is already
+      pre-programmed by the factory. Some flashes might provide both.
+
+    properties:
+      compatible:
+        enum:
+          - mtd-user-otp
+          - mtd-factory-otp
+
+    required:
+      - compatible
+
 additionalProperties: true
 
 examples:
@@ -36,4 +55,35 @@ examples:
         };
     };
 
+  - |
+    spi {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        flash@0 {
+            reg = <0>;
+            compatible = "jedec,spi-nor";
+
+            otp-1 {
+                compatible = "mtd-factory-otp";
+                #address-cells = <1>;
+                #size-cells = <1>;
+
+                electronic-serial-number@0 {
+                    reg = <0 8>;
+                };
+            };
+
+            otp-2 {
+                compatible = "mtd-user-otp";
+                #address-cells = <1>;
+                #size-cells = <1>;
+
+                mac-address@0 {
+                    reg = <0 6>;
+                };
+            };
+        };
+    };
+
 ...
-- 
2.20.1


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Re: [PATCH 3/5] dt-bindings: mtd: add OTP bindings

[Rob Herring]

On Fri, 16 Apr 2021 13:49:26 +0200, Michael Walle wrote:
> Flash devices can have one-time-programmable regions. Add a nvmem
> binding so they can be used as a nvmem provider.
> 
> Signed-off-by: Michael Walle <michael@walle.cc>
> ---
> Changes since RFC:
>  - added missing "$"
>  - dropped first example
>  - use real device compatibles
> 
>    Please note, that this will lead to an error without patch 4/5, which
>    introduces that property for the jedec,spi-nor. Should I keep it
>    seperate or should I squash that patch into this one?
> 
>  .../devicetree/bindings/mtd/mtd.yaml          | 50 +++++++++++++++++++
>  1 file changed, 50 insertions(+)
> 

My bot found errors running 'make DT_CHECKER_FLAGS=-m dt_binding_check'
on your patch (DT_CHECKER_FLAGS is new in v5.13):

yamllint warnings/errors:

dtschema/dtc warnings/errors:
/builds/robherring/linux-dt-review/Documentation/devicetree/bindings/mtd/mtd.example.dt.yaml: flash@0: 'otp-1', 'otp-2' do not match any of the regexes: '^partition@', 'pinctrl-[0-9]+'
	From schema: /builds/robherring/linux-dt-review/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml

See https://patchwork.ozlabs.org/patch/1467024

This check can fail if there are any dependencies. The base for a patch
series is generally the most recent rc1.

If you already ran 'make dt_binding_check' and didn't see the above
error(s), then make sure 'yamllint' is installed and dt-schema is up to
date:

pip3 install dtschema --upgrade

Please check and re-submit.


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Re: [PATCH 3/5] dt-bindings: mtd: add OTP bindings

[Rob Herring]

On Fri, Apr 16, 2021 at 01:30:01PM -0500, Rob Herring wrote:
> On Fri, 16 Apr 2021 13:49:26 +0200, Michael Walle wrote:
> > Flash devices can have one-time-programmable regions. Add a nvmem
> > binding so they can be used as a nvmem provider.
> > 
> > Signed-off-by: Michael Walle <michael@walle.cc>
> > ---
> > Changes since RFC:
> >  - added missing "$"
> >  - dropped first example
> >  - use real device compatibles
> > 
> >    Please note, that this will lead to an error without patch 4/5, which
> >    introduces that property for the jedec,spi-nor. Should I keep it
> >    seperate or should I squash that patch into this one?
> > 
> >  .../devicetree/bindings/mtd/mtd.yaml          | 50 +++++++++++++++++++
> >  1 file changed, 50 insertions(+)
> > 
> 
> My bot found errors running 'make DT_CHECKER_FLAGS=-m dt_binding_check'
> on your patch (DT_CHECKER_FLAGS is new in v5.13):
> 
> yamllint warnings/errors:
> 
> dtschema/dtc warnings/errors:
> /builds/robherring/linux-dt-review/Documentation/devicetree/bindings/mtd/mtd.example.dt.yaml: flash@0: 'otp-1', 'otp-2' do not match any of the regexes: '^partition@', 'pinctrl-[0-9]+'
> 	From schema: /builds/robherring/linux-dt-review/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml

Don't worry about this one if the series passes. There's not really a 
good way to avoid it other than moving the example.

Rob

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[PATCH 4/5] dt-bindings: mtd: spi-nor: add otp property

[Michael Walle]

SPI-NOR flashes may have OTP regions and have a nvmem binding. This
binding is described in mtd.yaml.

Signed-off-by: Michael Walle <michael@walle.cc>
---
Changes since RFC:
 - new patch

 Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml b/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml
index 5e7e5349f9a1..ed590d7c6e37 100644
--- a/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml
+++ b/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml
@@ -9,6 +9,9 @@ title: SPI NOR flash ST M25Pxx (and similar) serial flash chips
 maintainers:
   - Rob Herring <robh@kernel.org>
 
+allOf:
+  - $ref: "mtd.yaml#"
+
 properties:
   compatible:
     oneOf:
@@ -82,6 +85,9 @@ patternProperties:
   '^partition@':
     type: object
 
+  "^otp(-[0-9]+)?$":
+    type: object
+
 additionalProperties: false
 
 examples:
-- 
2.20.1


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Re: [PATCH 4/5] dt-bindings: mtd: spi-nor: add otp property

[Rob Herring]

On Fri, 16 Apr 2021 13:49:27 +0200, Michael Walle wrote:
> SPI-NOR flashes may have OTP regions and have a nvmem binding. This
> binding is described in mtd.yaml.
> 
> Signed-off-by: Michael Walle <michael@walle.cc>
> ---
> Changes since RFC:
>  - new patch
> 
>  Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml | 6 ++++++
>  1 file changed, 6 insertions(+)
> 

My bot found errors running 'make DT_CHECKER_FLAGS=-m dt_binding_check'
on your patch (DT_CHECKER_FLAGS is new in v5.13):

yamllint warnings/errors:

dtschema/dtc warnings/errors:
Unknown file referenced: [Errno 2] No such file or directory: '/usr/local/lib/python3.8/dist-packages/dtschema/schemas/mtd/mtd.yaml'
xargs: dt-doc-validate: exited with status 255; aborting
make[1]: *** Deleting file 'Documentation/devicetree/bindings/spi/st,stm32-qspi.example.dt.yaml'
Unknown file referenced: [Errno 2] No such file or directory: '/usr/local/lib/python3.8/dist-packages/dtschema/schemas/mtd/mtd.yaml'
make[1]: *** [scripts/Makefile.lib:377: Documentation/devicetree/bindings/spi/st,stm32-qspi.example.dt.yaml] Error 255
make[1]: *** Waiting for unfinished jobs....
make[1]: *** Deleting file 'Documentation/devicetree/bindings/spi/qcom,spi-qcom-qspi.example.dt.yaml'
Unknown file referenced: [Errno 2] No such file or directory: '/usr/local/lib/python3.8/dist-packages/dtschema/schemas/mtd/mtd.yaml'
make[1]: *** [scripts/Makefile.lib:377: Documentation/devicetree/bindings/spi/qcom,spi-qcom-qspi.example.dt.yaml] Error 255
make: *** [Makefile:1414: dt_binding_check] Error 2

See https://patchwork.ozlabs.org/patch/1467025

This check can fail if there are any dependencies. The base for a patch
series is generally the most recent rc1.

If you already ran 'make dt_binding_check' and didn't see the above
error(s), then make sure 'yamllint' is installed and dt-schema is up to
date:

pip3 install dtschema --upgrade

Please check and re-submit.


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[PATCH 5/5] mtd: core: add OTP nvmem provider support

[Michael Walle]

Flash OTP regions can already be read via user space. Some boards have
their serial number or MAC addresses stored in the OTP regions. Add
support for them being a (read-only) nvmem provider.

The API to read the OTP data is already in place. It distinguishes
between factory and user OTP, thus there are up to two different
providers.

Signed-off-by: Michael Walle <michael@walle.cc>
---
Changes since RFC:
 - none

 drivers/mtd/mtdcore.c   | 149 ++++++++++++++++++++++++++++++++++++++++
 include/linux/mtd/mtd.h |   2 +
 2 files changed, 151 insertions(+)

diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
index 0bc6871c3863..92201e3d187a 100644
--- a/drivers/mtd/mtdcore.c
+++ b/drivers/mtd/mtdcore.c
@@ -777,6 +777,147 @@ static void mtd_set_dev_defaults(struct mtd_info *mtd)
 	mutex_init(&mtd->master.chrdev_lock);
 }
 
+static ssize_t mtd_otp_size(struct mtd_info *mtd, bool is_user)
+{
+	struct otp_info *info = kmalloc(PAGE_SIZE, GFP_KERNEL);
+	ssize_t size = 0;
+	unsigned int i;
+	size_t retlen;
+	int ret;
+
+	if (is_user)
+		ret = mtd_get_user_prot_info(mtd, PAGE_SIZE, &retlen, info);
+	else
+		ret = mtd_get_fact_prot_info(mtd, PAGE_SIZE, &retlen, info);
+	if (ret)
+		goto err;
+
+	for (i = 0; i < retlen / sizeof(*info); i++) {
+		size += info->length;
+		info++;
+	}
+
+	kfree(info);
+	return size;
+
+err:
+	kfree(info);
+	return ret;
+}
+
+static struct nvmem_device *mtd_otp_nvmem_register(struct mtd_info *mtd,
+						   const char *name, int size,
+						   nvmem_reg_read_t reg_read,
+						   const char *compatible)
+{
+	struct nvmem_device *nvmem = NULL;
+	struct nvmem_config config = {};
+	struct device_node *np;
+
+	/* DT binding is optional */
+	np = of_get_compatible_child(mtd->dev.of_node, compatible);
+
+	/* OTP nvmem will be registered on the physical device */
+	config.dev = mtd->dev.parent;
+	config.name = name;
+	config.id = NVMEM_DEVID_NONE;
+	config.owner = THIS_MODULE;
+	config.type = NVMEM_TYPE_OTP;
+	config.root_only = true;
+	config.reg_read = reg_read;
+	config.size = size;
+	config.of_node = np;
+	config.priv = mtd;
+
+	nvmem = nvmem_register(&config);
+	/* Just ignore if there is no NVMEM support in the kernel */
+	if (IS_ERR(nvmem) && PTR_ERR(nvmem) == -EOPNOTSUPP)
+		nvmem = NULL;
+
+	of_node_put(np);
+
+	return nvmem;
+}
+
+static int mtd_nvmem_user_otp_reg_read(void *priv, unsigned int offset,
+				       void *val, size_t bytes)
+{
+	struct mtd_info *mtd = priv;
+	size_t retlen;
+	int ret;
+
+	ret = mtd_read_user_prot_reg(mtd, offset, bytes, &retlen, val);
+	if (ret)
+		return ret;
+
+	return retlen == bytes ? 0 : -EIO;
+}
+
+static int mtd_nvmem_fact_otp_reg_read(void *priv, unsigned int offset,
+				       void *val, size_t bytes)
+{
+	struct mtd_info *mtd = priv;
+	size_t retlen;
+	int ret;
+
+	ret = mtd_read_fact_prot_reg(mtd, offset, bytes, &retlen, val);
+	if (ret)
+		return ret;
+
+	return retlen == bytes ? 0 : -EIO;
+}
+
+static int mtd_otp_nvmem_add(struct mtd_info *mtd)
+{
+	struct nvmem_device *nvmem;
+	ssize_t size;
+	int err;
+
+	if (mtd->_get_user_prot_info && mtd->_read_user_prot_reg) {
+		size = mtd_otp_size(mtd, true);
+		if (size < 0)
+			return size;
+
+		if (size > 0) {
+			nvmem = mtd_otp_nvmem_register(mtd, "user-otp", size,
+						       mtd_nvmem_user_otp_reg_read,
+						       "mtd-user-otp");
+			if (IS_ERR(nvmem)) {
+				dev_err(&mtd->dev, "Failed to register OTP NVMEM device\n");
+				return PTR_ERR(nvmem);
+			}
+			mtd->otp_user_nvmem = nvmem;
+		}
+	}
+
+	if (mtd->_get_fact_prot_info && mtd->_read_fact_prot_reg) {
+		size = mtd_otp_size(mtd, false);
+		if (size < 0) {
+			err = size;
+			goto err;
+		}
+
+		if (size > 0) {
+			nvmem = mtd_otp_nvmem_register(mtd, "factory-otp", size,
+						       mtd_nvmem_fact_otp_reg_read,
+						       "mtd-factory-otp");
+			if (IS_ERR(nvmem)) {
+				dev_err(&mtd->dev, "Failed to register OTP NVMEM device\n");
+				err = PTR_ERR(nvmem);
+				goto err;
+			}
+			mtd->otp_factory_nvmem = nvmem;
+		}
+	}
+
+	return 0;
+
+err:
+	if (mtd->otp_user_nvmem)
+		nvmem_unregister(mtd->otp_user_nvmem);
+	return err;
+}
+
 /**
  * mtd_device_parse_register - parse partitions and register an MTD device.
  *
@@ -852,6 +993,8 @@ int mtd_device_parse_register(struct mtd_info *mtd, const char * const *types,
 		register_reboot_notifier(&mtd->reboot_notifier);
 	}
 
+	ret = mtd_otp_nvmem_add(mtd);
+
 out:
 	if (ret && device_is_registered(&mtd->dev))
 		del_mtd_device(mtd);
@@ -873,6 +1016,12 @@ int mtd_device_unregister(struct mtd_info *master)
 	if (master->_reboot)
 		unregister_reboot_notifier(&master->reboot_notifier);
 
+	if (master->otp_user_nvmem)
+		nvmem_unregister(master->otp_user_nvmem);
+
+	if (master->otp_factory_nvmem)
+		nvmem_unregister(master->otp_factory_nvmem);
+
 	err = del_mtd_partitions(master);
 	if (err)
 		return err;
diff --git a/include/linux/mtd/mtd.h b/include/linux/mtd/mtd.h
index 4aac200ca8b5..71e751d18c22 100644
--- a/include/linux/mtd/mtd.h
+++ b/include/linux/mtd/mtd.h
@@ -379,6 +379,8 @@ struct mtd_info {
 	int usecount;
 	struct mtd_debug_info dbg;
 	struct nvmem_device *nvmem;
+	struct nvmem_device *otp_user_nvmem;
+	struct nvmem_device *otp_factory_nvmem;
 
 	/*
 	 * Parent device from the MTD partition point of view.
-- 
2.20.1


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Re: [PATCH 0/5] mtd: core: OTP nvmem provider support

[Rob Herring]

On Fri, Apr 16, 2021 at 01:49:23PM +0200, Michael Walle wrote:
> The goal is to fetch a (base) MAC address from the OTP region of a SPI NOR
> flash.
> 
> This is the first part, where I try to add the nvmem provider support to
> the MTD core.
> 
> I'm not sure about the device tree bindings. Consider the following two
> variants:
> 
> (1)
>     flash@0 {
>         ..
> 
>         otp {
>             compatible = "mtd-user-otp";

mtd is a linuxism. Why not just 'nvmem-cells' here or as a fallback if 
we come up with a better name? 

>             #address-cells = <1>;
>             #size-cells = <1>;
> 
>             serial-number@0 {
>                 reg = <0x0 0x8>;
>             };
>         };
>     };
> 
> (2)
>     flash@0 {
>         ..
> 
>         otp {
>             compatible = "mtd-user-otp";
>             #address-cells = <1>;
>             #size-cells = <1>;
> 
> 			some-useful-name {
>                 compatible = "nvmem-cells";
> 
>                 serial-number@0 {
>                     reg = <0x0 0x8>;
>                 };
> 			};
>         };
>     };
> 
> Both bindings use a subnode "opt[-N]". We cannot have the nvmem cells as
> children to the flash node because of the legacy partition binding.
> 
> (1) seems to be the form which is used almost everywhere in the kernel.
> That is, the nvmem cells are just children of the parent node.
> 
> (2) seem to be more natural, because there might also be other properties
> inside the otp subnode and might be more future-proof.
> 
> At the moment this patch implements (1).

I think approach (1) seems fine.

Rob

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Re: [PATCH 0/5] mtd: core: OTP nvmem provider support

[Michael Walle]

Hi Rob,

Am 2021-04-16 20:44, schrieb Rob Herring:
> On Fri, Apr 16, 2021 at 01:49:23PM +0200, Michael Walle wrote:
>> The goal is to fetch a (base) MAC address from the OTP region of a SPI 
>> NOR
>> flash.
>> 
>> This is the first part, where I try to add the nvmem provider support 
>> to
>> the MTD core.
>> 
>> I'm not sure about the device tree bindings. Consider the following 
>> two
>> variants:
>> 
>> (1)
>>     flash@0 {
>>         ..
>> 
>>         otp {
>>             compatible = "mtd-user-otp";
> 
> mtd is a linuxism. Why not just 'nvmem-cells' here or as a fallback if
> we come up with a better name?

There are two different compatibles: "mtd-user-otp" and 
"mtd-factory-otp"
to differentiate what kind of OTP should be used (and both are possible
at the same time). Thus nvmem-cells alone won't be enough. We could drop
the "mtd-" prefix though.

Is there a benefit of having the following?
   compatible = "user-otp", "nvmem-cells";


>>             #address-cells = <1>;
>>             #size-cells = <1>;
>> 
>>             serial-number@0 {
>>                 reg = <0x0 0x8>;
>>             };
>>         };
>>     };
>> 
>> (2)
>>     flash@0 {
>>         ..
>> 
>>         otp {
>>             compatible = "mtd-user-otp";
>>             #address-cells = <1>;
>>             #size-cells = <1>;
>> 
>> 			some-useful-name {
>>                 compatible = "nvmem-cells";
>> 
>>                 serial-number@0 {
>>                     reg = <0x0 0x8>;
>>                 };
>> 			};
>>         };
>>     };
>> 
>> Both bindings use a subnode "opt[-N]". We cannot have the nvmem cells 
>> as
>> children to the flash node because of the legacy partition binding.
>> 
>> (1) seems to be the form which is used almost everywhere in the 
>> kernel.
>> That is, the nvmem cells are just children of the parent node.
>> 
>> (2) seem to be more natural, because there might also be other 
>> properties
>> inside the otp subnode and might be more future-proof.
>> 
>> At the moment this patch implements (1).
> 
> I think approach (1) seems fine.

ok

-michael

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Re: [PATCH 0/5] mtd: core: OTP nvmem provider support

[Rob Herring]

On Fri, Apr 16, 2021 at 09:26:03PM +0200, Michael Walle wrote:
> Hi Rob,
> 
> Am 2021-04-16 20:44, schrieb Rob Herring:
> > On Fri, Apr 16, 2021 at 01:49:23PM +0200, Michael Walle wrote:
> > > The goal is to fetch a (base) MAC address from the OTP region of a
> > > SPI NOR
> > > flash.
> > > 
> > > This is the first part, where I try to add the nvmem provider
> > > support to
> > > the MTD core.
> > > 
> > > I'm not sure about the device tree bindings. Consider the following
> > > two
> > > variants:
> > > 
> > > (1)
> > >     flash@0 {
> > >         ..
> > > 
> > >         otp {
> > >             compatible = "mtd-user-otp";
> > 
> > mtd is a linuxism. Why not just 'nvmem-cells' here or as a fallback if
> > we come up with a better name?
> 
> There are two different compatibles: "mtd-user-otp" and "mtd-factory-otp"
> to differentiate what kind of OTP should be used (and both are possible
> at the same time). Thus nvmem-cells alone won't be enough. We could drop
> the "mtd-" prefix though.
> 
> Is there a benefit of having the following?
>   compatible = "user-otp", "nvmem-cells";

Yes. I assume 'user-otp' tells you something about the region and 
'nvmem-cells' tells you that there are child nodes of nvmem data. Of 
course 'user-otp' could imply 'nvmem-cells' as you did. I'm fine with 
either way.

Rob

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Re: [PATCH 0/5] mtd: core: OTP nvmem provider support

[Michael Walle]

Hi Rob,

Am 2021-04-20 16:08, schrieb Rob Herring:
> On Fri, Apr 16, 2021 at 09:26:03PM +0200, Michael Walle wrote:
>> Am 2021-04-16 20:44, schrieb Rob Herring:
>> > On Fri, Apr 16, 2021 at 01:49:23PM +0200, Michael Walle wrote:
>> > > The goal is to fetch a (base) MAC address from the OTP region of a
>> > > SPI NOR
>> > > flash.
>> > >
>> > > This is the first part, where I try to add the nvmem provider
>> > > support to
>> > > the MTD core.
>> > >
>> > > I'm not sure about the device tree bindings. Consider the following
>> > > two
>> > > variants:
>> > >
>> > > (1)
>> > >     flash@0 {
>> > >         ..
>> > >
>> > >         otp {
>> > >             compatible = "mtd-user-otp";
>> >
>> > mtd is a linuxism. Why not just 'nvmem-cells' here or as a fallback if
>> > we come up with a better name?
>> 
>> There are two different compatibles: "mtd-user-otp" and 
>> "mtd-factory-otp"
>> to differentiate what kind of OTP should be used (and both are 
>> possible
>> at the same time). Thus nvmem-cells alone won't be enough. We could 
>> drop
>> the "mtd-" prefix though.
>> 
>> Is there a benefit of having the following?
>>   compatible = "user-otp", "nvmem-cells";
> 
> Yes. I assume 'user-otp' tells you something about the region and
> 'nvmem-cells' tells you that there are child nodes of nvmem data. Of
> course 'user-otp' could imply 'nvmem-cells' as you did. I'm fine with
> either way.

Ah, if I use both compatibles, then the
Documentation/devicetree/bindings/mtd/partitions/nvmem-cells.yaml
schema kicks in, which mandates 'compatible = "nvmem-cells";' and I
get the following errors:

   CHECK   Documentation/devicetree/bindings/mtd/mtd.example.dt.yaml
/home/mwalle/repos/b-linux-arm64/Documentation/devicetree/bindings/mtd/mtd.example.dt.yaml: 
otp-1: compatible:0: 'nvmem-cells' was expected
	From schema: 
/home/mwalle/repos/linux-mw/Documentation/devicetree/bindings/mtd/partitions/nvmem-cells.yaml
/home/mwalle/repos/b-linux-arm64/Documentation/devicetree/bindings/mtd/mtd.example.dt.yaml: 
otp-1: compatible: ['factory-otp', 'nvmem-cells'] is too long
	From schema: 
/home/mwalle/repos/linux-mw/Documentation/devicetree/bindings/mtd/partitions/nvmem-cells.yaml
/home/mwalle/repos/b-linux-arm64/Documentation/devicetree/bindings/mtd/mtd.example.dt.yaml: 
otp-1: compatible: Additional items are not allowed ('nvmem-cells' was 
unexpected)
	From schema: 
/home/mwalle/repos/linux-mw/Documentation/devicetree/bindings/mtd/partitions/nvmem-cells.yaml

Is there a way around that?

-michael

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