linux-kernel - Re: [PATCH 1/3] dt-bindings: nvmem: u-boot,env: Add support for u-boot,env-size

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Message-ID: <20230726163600.GA1549714-robh@kernel.org>
Date:   Wed, 26 Jul 2023 10:36:00 -0600
From:   Rob Herring <robh@...nel.org>
To:     Christian Marangi <ansuelsmth@...il.com>
Cc:     Rafał Miłecki <rafal@...ecki.pl>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] dt-bindings: nvmem: u-boot,env: Add support for
 u-boot,env-size

On Mon, Jul 24, 2023 at 10:26:30AM +0200, Christian Marangi wrote:
> Add support for u-boot,env-size new property.
> 
> Permit to declare a custom size of the U-Boot env that differs than the
> partition size where the U-Boot env is located.
> 
> U-Boot env is validated by calculating the CRC32 on the entire env
> and in some specific case, the env size might differ from the partition
> size resulting in wrong CRC32 calculation than the expected one saved at
> the start of the partition.

Why can't you just change the partition size? There is no size really 
because it is just defined in DT.
> 
> This happens when U-Boot is compiled by hardcoding a specific env size
> but the env is actually placed in a bigger partition, resulting in needing
> to provide a custom value.

If u-boot is compiled that way, then shouldn't it have that size 
contained within it? What happens when the DT doesn't match?

> 
> Declaring this property, this value will be used for NVMEM size instead of
> the mtd partition.
> 
> Add also an example to make it clear the scenario of mismatched
> partition size and actual U-Boot env.

If we do have this, then perhaps there is a generic need for a data 
size property.

> 
> Signed-off-by: Christian Marangi <ansuelsmth@...il.com>
> ---
>  .../devicetree/bindings/nvmem/u-boot,env.yaml | 47 +++++++++++++++++++
>  1 file changed, 47 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/nvmem/u-boot,env.yaml b/Documentation/devicetree/bindings/nvmem/u-boot,env.yaml
> index 36d97fb87865..3970725a2c57 100644
> --- a/Documentation/devicetree/bindings/nvmem/u-boot,env.yaml
> +++ b/Documentation/devicetree/bindings/nvmem/u-boot,env.yaml
> @@ -44,6 +44,24 @@ properties:
>    reg:
>      maxItems: 1
>  
> +  u-boot,env-size:
> +    description: |
> +      Permit to declare a custom size of the U-Boot env that differs than the
> +      partition size where the U-Boot env is located.
> +
> +      U-Boot env is validated by calculating the CRC32 on the entire env
> +      and in some specific case, the env size might differ from the partition
> +      size resulting in wrong CRC32 calculation than the expected one saved at
> +      the start of the partition.
> +
> +      This happens when U-Boot is compiled by hardcoding a specific env size
> +      but the env is actually placed in a bigger partition, resulting in needing
> +      to provide a custom value.
> +
> +      Declaring this property, this value will be used for NVMEM size instead of
> +      the mtd partition.
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +
>    bootcmd:
>      type: object
>      description: Command to use for automatic booting
> @@ -99,3 +117,32 @@ examples:
>              };
>          };
>      };
> +  - |
> +    partitions {
> +        compatible = "fixed-partitions";
> +        #address-cells = <1>;
> +        #size-cells = <1>;
> +
> +        partition@0 {
> +            reg = <0x0 0xc80000>;
> +            label = "qcadata";
> +            read-only;
> +        };
> +
> +        partition@...000 {
> +            label = "APPSBL";
> +            reg = <0xc80000 0x500000>;
> +            read-only;
> +        };
> +
> +        partition@...0000 {
> +            compatible = "u-boot,env";
> +            reg = <0x1180000 0x80000>;
> +
> +            u-boot,env-size = <0x40000>;
> +
> +            mac1: ethaddr {
> +                #nvmem-cell-cells = <1>;
> +            };
> +        };
> +    };
> -- 
> 2.40.1
>