[PATCH 1/2] nvmem: u-boot-env: support specifying the env storage size

[PATCH 1/2] nvmem: u-boot-env: support specifying the env storage size

[Shiji Yang]

In the current code, we always assume that the env storage size is
the same as the mtd partition size. U-boot supports customizing the
size of the environment area. If its size is different from the MTD
partition size. This will result in CRC32 verification error. This
patch will introduce a new property env-size to give users a chance
to configure the correct env storage size.

Signed-off-by: Shiji Yang <yangshiji66@outlook.com>
---
 drivers/nvmem/u-boot-env.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/nvmem/u-boot-env.c b/drivers/nvmem/u-boot-env.c
index ced414fc9..ac9858010 100644
--- a/drivers/nvmem/u-boot-env.c
+++ b/drivers/nvmem/u-boot-env.c
@@ -52,6 +52,7 @@ static int u_boot_env_probe(struct platform_device *pdev)
 	struct device *dev = &pdev->dev;
 	struct device_node *np = dev->of_node;
 	struct u_boot_env *priv;
+	u32 env_size;
 
 	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
 	if (!priv)
@@ -68,7 +69,12 @@ static int u_boot_env_probe(struct platform_device *pdev)
 
 	config.dev = dev;
 	config.priv = priv;
-	config.size = priv->mtd->size;
+
+	if (!of_property_read_u32(np, "env-size", &env_size) &&
+	    env_size <= priv->mtd->size)
+		config.size = env_size;
+	else
+		config.size = priv->mtd->size;
 
 	priv->nvmem = devm_nvmem_register(dev, &config);
 	if (IS_ERR(priv->nvmem))
-- 
2.50.0

[PATCH 2/2] dt-bindings: nvmem: add env-size property for u-boot env layout

[Shiji Yang]

This newly introduced property allows users to declare the size of
the environment storage area.

Signed-off-by: Shiji Yang <yangshiji66@outlook.com>
---
 .../devicetree/bindings/nvmem/layouts/u-boot,env.yaml      | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/Documentation/devicetree/bindings/nvmem/layouts/u-boot,env.yaml b/Documentation/devicetree/bindings/nvmem/layouts/u-boot,env.yaml
index 56a8f55d4..e0b65a53e 100644
--- a/Documentation/devicetree/bindings/nvmem/layouts/u-boot,env.yaml
+++ b/Documentation/devicetree/bindings/nvmem/layouts/u-boot,env.yaml
@@ -46,6 +46,12 @@ properties:
     type: object
     description: Command to use for automatic booting
 
+  env-size:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    description:
+      Size of the environment storage area in bytes. If this property
+      is not defined, the default size is the partition size.
+
   ethaddr:
     type: object
     description: Ethernet interfaces base MAC address.
@@ -85,6 +91,7 @@ examples:
         env: partition@40000 {
             compatible = "u-boot,env";
             reg = <0x40000 0x10000>;
+            env-size = <0x1000>;
 
             mac: ethaddr {
                 #nvmem-cell-cells = <1>;
-- 
2.50.0

Re: [PATCH 2/2] dt-bindings: nvmem: add env-size property for u-boot env layout

[Krzysztof Kozlowski]

On 30/07/2025 15:17, Shiji Yang wrote:
> This newly introduced property allows users to declare the size of
> the environment storage area.

Bindings come before the user.

Your commit msg should explain WHY you are doing this, not what you did
here. I see from the diff everything what you said above. I don't see
the reason to limit the env size.

Best regards,
Krzysztof

Re: [PATCH 2/2] dt-bindings: nvmem: add env-size property for u-boot env layout

[Rob Herring]

On Wed, Jul 30, 2025 at 09:17:47PM +0800, Shiji Yang wrote:
> This newly introduced property allows users to declare the size of
> the environment storage area.

Why do you need it to be less than the partition size? They commit msg 
needs to explain that.

The partition size for fixed partitions in particular are purely a DT 
construct. No reason the partition size can't always be the env size.

> Signed-off-by: Shiji Yang <yangshiji66@outlook.com>
> ---
>  .../devicetree/bindings/nvmem/layouts/u-boot,env.yaml      | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/nvmem/layouts/u-boot,env.yaml b/Documentation/devicetree/bindings/nvmem/layouts/u-boot,env.yaml
> index 56a8f55d4..e0b65a53e 100644
> --- a/Documentation/devicetree/bindings/nvmem/layouts/u-boot,env.yaml
> +++ b/Documentation/devicetree/bindings/nvmem/layouts/u-boot,env.yaml
> @@ -46,6 +46,12 @@ properties:
>      type: object
>      description: Command to use for automatic booting
>  
> +  env-size:
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    description:
> +      Size of the environment storage area in bytes. If this property
> +      is not defined, the default size is the partition size.
> +
>    ethaddr:
>      type: object
>      description: Ethernet interfaces base MAC address.
> @@ -85,6 +91,7 @@ examples:
>          env: partition@40000 {
>              compatible = "u-boot,env";
>              reg = <0x40000 0x10000>;
> +            env-size = <0x1000>;
>  
>              mac: ethaddr {
>                  #nvmem-cell-cells = <1>;
> -- 
> 2.50.0
> 

Re: [PATCH 2/2] dt-bindings: nvmem: add env-size property for u-boot env layout

[Alexander Dahl]

Hei hei,

just hooking in, because it relates to a U-Boot feature I'm using, too.

Am Wed, Jul 30, 2025 at 06:52:14PM -0500 schrieb Rob Herring:
> On Wed, Jul 30, 2025 at 09:17:47PM +0800, Shiji Yang wrote:
> > This newly introduced property allows users to declare the size of
> > the environment storage area.
> 
> Why do you need it to be less than the partition size? They commit msg 
> needs to explain that.

+1

> The partition size for fixed partitions in particular are purely a DT 
> construct. No reason the partition size can't always be the env size.

You can set CONFIG_ENV_RANGE and CONFIG_ENV_SIZE to different values
in U-Boot to allow bad block handling.  I have a board here where the
U-Boot env is stored directly in NAND flash.  The mtd partition size
is 2 times the nand block size (ENV_RANGE=0x40000) while the env size
is exactly one nand block size (ENV_SIZE=0x20000).  So the partition
is 2 blocks, but the env size is only 1 block.  This way the first
block can become bad and U-Boot will skip it and use the second block.
This would not be possible if the env would always use the whole
partition.  The usable size of the partition would be too small to
keep the env then.

The help text for this is present in U-Boot since 2010, so I guess the
feature is there even longer:

  - CONFIG_ENV_RANGE (optional):
  
    Specifies the length of the region in which the environment
    can be written.  This should be a multiple of the NAND device's
    block size.  Specifying a range with more erase blocks than
    are needed to hold CONFIG_ENV_SIZE allows bad blocks within
    the range to be avoided.

HTH & Greets
Alex

> 
> > Signed-off-by: Shiji Yang <yangshiji66@outlook.com>
> > ---
> >  .../devicetree/bindings/nvmem/layouts/u-boot,env.yaml      | 7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/nvmem/layouts/u-boot,env.yaml b/Documentation/devicetree/bindings/nvmem/layouts/u-boot,env.yaml
> > index 56a8f55d4..e0b65a53e 100644
> > --- a/Documentation/devicetree/bindings/nvmem/layouts/u-boot,env.yaml
> > +++ b/Documentation/devicetree/bindings/nvmem/layouts/u-boot,env.yaml
> > @@ -46,6 +46,12 @@ properties:
> >      type: object
> >      description: Command to use for automatic booting
> >  
> > +  env-size:
> > +    $ref: /schemas/types.yaml#/definitions/uint32
> > +    description:
> > +      Size of the environment storage area in bytes. If this property
> > +      is not defined, the default size is the partition size.
> > +
> >    ethaddr:
> >      type: object
> >      description: Ethernet interfaces base MAC address.
> > @@ -85,6 +91,7 @@ examples:
> >          env: partition@40000 {
> >              compatible = "u-boot,env";
> >              reg = <0x40000 0x10000>;
> > +            env-size = <0x1000>;
> >  
> >              mac: ethaddr {
> >                  #nvmem-cell-cells = <1>;
> > -- 
> > 2.50.0
> > 
>