linux-kernel - Re: [PATCH 2/3] dt-bindings: mtd: Add a property to declare secure regions in Qcom NANDc

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Date:   Tue, 23 Feb 2021 17:49:22 +0100
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     richard@....at, vigneshr@...com, robh+dt@...nel.org,
        linux-arm-msm@...r.kernel.org, linux-mtd@...ts.infradead.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        boris.brezillon@...labora.com
Subject: Re: [PATCH 2/3] dt-bindings: mtd: Add a property to declare secure
 regions in Qcom NANDc

Hi Manivannan,

Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org> wrote on Mon,
22 Feb 2021 17:32:58 +0530:

> On a typical end product, a vendor may choose to secure some regions in
> the NAND memory which are supposed to stay intact between FW upgrades.
> The access to those regions will be blocked by a secure element like
> Trustzone. So the normal world software like Linux kernel should not
> touch these regions (including reading).
> 
> So let's add a property for declaring such secure regions so that the
> driver can skip touching them.
> 
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> ---
>  Documentation/devicetree/bindings/mtd/qcom,nandc.yaml | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/mtd/qcom,nandc.yaml b/Documentation/devicetree/bindings/mtd/qcom,nandc.yaml
> index 84ad7ff30121..7500e20da9c1 100644
> --- a/Documentation/devicetree/bindings/mtd/qcom,nandc.yaml
> +++ b/Documentation/devicetree/bindings/mtd/qcom,nandc.yaml
> @@ -48,6 +48,13 @@ patternProperties:
>          enum:
>            - 512
>  
> +      qcom,secure-regions:
> +        $ref: /schemas/types.yaml#/definitions/uint32-array
> +        description:
> +          Regions in the NAND memory which are protected using a secure element
> +          like Trustzone. This property contains the start address and size of
> +          the secure regions present (optional).

What does this "(optional)" means? If you mean the property is optional
then it should be described accordingly in the yaml file, or am I
missing something?

I wonder if it wouldn't be better to make this a NAND chip node
property. I don't think a qcom prefix is needed as potentially many
other SoCs might have the same "feature".

I'm fine adding support for it in the qcom driver only though.

> +
>  allOf:
>    - $ref: "nand-controller.yaml#"
>  

Thanks,
Miquèl