linux-kernel - Re: [PATCH v3 1/2] dt-bindings: exynos-dw-mshc-common: add exynos78xx variants

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Date:   Sun, 12 Mar 2023 14:35:01 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Sergey Lisov <sleirsgoevy@...il.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Jaehoon Chung <jh80.chung@...sung.com>
Cc:     linux-mmc@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] dt-bindings: exynos-dw-mshc-common: add exynos78xx
 variants

On 12/03/2023 14:03, Sergey Lisov wrote:
> Some Samsung Exynos boards using the arm64 architecture have DW MMC
> controllers configured for a 32-bit data bus but a 64-bit FIFO. On these
> systems the 64-bit FIFO registers must be accessed in two 32-bit halves.
> 
> Add two new compatible strings, "samsung,exynos78xx-dw-mshc" and
> "samsung,exynos78xx-dw-mshc-smu" respectively, to denote exynos78xx
> boards that need this quirk. But it's very possible that all
> "samsung,exynos7-dw-mshc" boards are actually affected.
> ---
>  .../devicetree/bindings/mmc/samsung,exynos-dw-mshc.yaml         | 2 ++
>  arch/arm64/boot/dts/exynos/exynos7885.dtsi                      | 2 +-

Bindings and DTS (and driver) are always separate.

>  2 files changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/devicetree/bindings/mmc/samsung,exynos-dw-mshc.yaml b/Documentation/devicetree/bindings/mmc/samsung,exynos-dw-mshc.yaml
> index fdaa18481..a72a67792 100644
> --- a/Documentation/devicetree/bindings/mmc/samsung,exynos-dw-mshc.yaml
> +++ b/Documentation/devicetree/bindings/mmc/samsung,exynos-dw-mshc.yaml
> @@ -22,6 +22,8 @@ properties:
>        - samsung,exynos5420-dw-mshc-smu
>        - samsung,exynos7-dw-mshc
>        - samsung,exynos7-dw-mshc-smu
> +      - samsung,exynos78xx-dw-mshc
> +      - samsung,exynos78xx-dw-mshc-smu

Compatibles must be specific.

There is also no fallback, but I assume that's intentional - you say
these are not compatible?

>        - axis,artpec8-dw-mshc
>  
>    reg:
> diff --git a/arch/arm64/boot/dts/exynos/exynos7885.dtsi b/arch/arm64/boot/dts/exynos/exynos7885.dtsi
> index 23c2e0bb0..4b94ac9da 100644
> --- a/arch/arm64/boot/dts/exynos/exynos7885.dtsi
> +++ b/arch/arm64/boot/dts/exynos/exynos7885.dtsi
> @@ -294,7 +294,7 @@ pmu_system_controller: system-controller@...80000 {
>  		};
>  
>  		mmc_0: mmc@...00000 {
> -			compatible = "samsung,exynos7-dw-mshc-smu";
> +			compatible = "samsung,exynos78xx-dw-mshc-smu";

That's non-bisectable change (also breaking other users of DTS), so you
need to explain in commit msg rationale - devices were never compatible
and using exynos7 does not work in certain cases.



Best regards,
Krzysztof