linux-kernel - Re: [PATCH v7 8/9] arm64: dts: qcom: sm6350: correct DP compatibility strings

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Message-ID: <37ax7uhzopemvmz5fgtayzz3hmnxmfcbyjhwgfgkdglynuo5oj@fud24vsqodnj>
Date: Tue, 2 Sep 2025 13:07:17 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc: Rob Clark <robin.clark@....qualcomm.com>,
        Dmitry Baryshkov <lumag@...nel.org>,
        Abhinav Kumar <abhinav.kumar@...ux.dev>,
        Jessica Zhang <jessica.zhang@....qualcomm.com>,
        Sean Paul <sean@...rly.run>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Kuogee Hsieh <quic_khsieh@...cinc.com>,
        Abel Vesa <abel.vesa@...aro.org>, Mahadevan <quic_mahap@...cinc.com>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>, linux-arm-msm@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 8/9] arm64: dts: qcom: sm6350: correct DP
 compatibility strings

On Tue, Sep 02, 2025 at 08:07:22AM +0200, Krzysztof Kozlowski wrote:
> On 02/09/2025 06:04, Dmitry Baryshkov wrote:
> >>>
> >>> diff --git a/arch/arm64/boot/dts/qcom/sm6350.dtsi b/arch/arm64/boot/dts/qcom/sm6350.dtsi
> >>> index 2493b9611dcb675f4c33794ecc0ee9e8823e24d4..8459b27cacc72a4827a2e289e669163ad6250059 100644
> >>> --- a/arch/arm64/boot/dts/qcom/sm6350.dtsi
> >>> +++ b/arch/arm64/boot/dts/qcom/sm6350.dtsi
> >>> @@ -2249,7 +2249,7 @@ opp-560000000 {
> >>>  			};
> >>>  
> >>>  			mdss_dp: displayport-controller@...0000 {
> >>> -				compatible = "qcom,sm6350-dp", "qcom,sm8350-dp";
> >>> +				compatible = "qcom,sm6350-dp", "qcom,sc7180-dp";
> >>
> >> No, that's breaking all the users.
> > 
> > WHy though? Both old and new lines are using fallbacks to bind the
> > driver to the device.
> 
> Kernel has sc7180 fallback, but what if other DTS user does not and that
> other user was relying on sm8350 fallback compatible? That other user
> won't have sm6350 dedicated handling as well.

Oh, a user which has SM8350 support, wants to support SM6350, but
doesn't support SC7180 DP? How hypothetical should be our users?

> 
> That breaking of users I meant.
> 
> With the kernel it should work, assuming SC7180-dp was introduced
> similar time as 8350-dp.

SC7180 DP was introduced several years ahead of SM8350, if my memory
doesn't deceive me.

> 
> Best regards,
> Krzysztof

-- 
With best wishes
Dmitry