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Tue, 02 Sep 2025 05:09:04 -0700 (PDT) Message-ID: Date: Tue, 2 Sep 2025 14:09:02 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7 2/9] dt-bindings: display/msm: dp-controller: fix fallback for SM6350 To: Dmitry Baryshkov Cc: Rob Clark , Dmitry Baryshkov , Abhinav Kumar , Jessica Zhang , Sean Paul , Marijn Suijten , David Airlie , Simona Vetter , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Kuogee Hsieh , Abel Vesa , Mahadevan , Bjorn Andersson , Konrad Dybcio , linux-arm-msm@vger.kernel.org, dri-devel@lists.freedesktop.org, freedreno@lists.freedesktop.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org References: <20250829-dp_mst_bindings-v7-0-2b268a43917b@oss.qualcomm.com> <20250829-dp_mst_bindings-v7-2-2b268a43917b@oss.qualcomm.com> <20250901-arboreal-gay-wolf-bcaaec@kuoka> <24999a53-ea5a-4823-a84f-2ca0ca184bb4@linaro.org> From: Krzysztof Kozlowski Content-Language: en-US Autocrypt: addr=krzysztof.kozlowski@linaro.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 02/09/2025 12:01, Dmitry Baryshkov wrote: > On Tue, Sep 02, 2025 at 08:04:54AM +0200, Krzysztof Kozlowski wrote: >> On 02/09/2025 06:03, Dmitry Baryshkov wrote: >>> On Mon, Sep 01, 2025 at 05:45:49AM +0200, Krzysztof Kozlowski wrote: >>>> On Fri, Aug 29, 2025 at 01:48:15AM +0300, Dmitry Baryshkov wrote: >>>>> The SM6350 doesn't have MST support, as such it is not compatible with >>>>> the SM8350 platform. Add new entry for SM6350 with fallback to SC7180 >>>>> (which belongs to the same generation and also doesn't have MST >>>>> support). >>>>> >>>>> Fixes: 39086151593a ("dt-bindings: display: msm: dp-controller: document SM6350 compatible") >>>>> Signed-off-by: Dmitry Baryshkov >>>>> --- >>>>> .../devicetree/bindings/display/msm/dp-controller.yaml | 14 +++++++++++++- >>>>> 1 file changed, 13 insertions(+), 1 deletion(-) >>>>> >>>>> diff --git a/Documentation/devicetree/bindings/display/msm/dp-controller.yaml b/Documentation/devicetree/bindings/display/msm/dp-controller.yaml >>>>> index aed3bafa67e3c24d2a876acd29660378b367603a..0f814aa6f51406fdbdd7386027f88dfbacb24392 100644 >>>>> --- a/Documentation/devicetree/bindings/display/msm/dp-controller.yaml >>>>> +++ b/Documentation/devicetree/bindings/display/msm/dp-controller.yaml >>>>> @@ -31,13 +31,25 @@ properties: >>>>> - qcom,sm8650-dp >>>>> - items: >>>>> - enum: >>>>> - - qcom,sar2130p-dp >>>>> - qcom,sm6350-dp >>>>> + - const: qcom,sc7180-dp >>>>> + >>>>> + # deprecated entry for compatibility with old DT >>>>> + - items: >>>>> + - enum: >>>>> + - qcom,sm6350-dp >>>>> + - const: qcom,sm8350-dp >>>>> + deprecated: true >>>> >>>> If it is only about bindings then there is little benefit in keeping >>>> this, just drop this case. However you cannot drop it from DTS, so this >>>> is a bit pointless. >>> >>> Our plan is: >>> - land updated DT bindings, describing MST clocks on MST-enabled >>> platforms, >>> - land updated DTS, adding MST clocks where applicable, >> >> This part breaks all out-of-tree users of DTS. > > User of which one? SM6350 or all DTS? SM6350. > > It extends the ABI, so no, it shouldn't. We add regions and clocks, No, it does not extend the ABI. You are changing the fallback, so you are changing the ABI. > existing users can use the previously defined feature set. > > Anyway, is it about adding more explicit note to the cover letter and/or > commit message or would you have any other proposal on how to handle the > issue? Please be explicit if Linux was working with the old fallback or not. In the DTS change be explicit about impact, e.g. that sc7180 fallback is there since forever. > >> >>> - land driver changes, keeping legacy support for non-MST DTs on >>> MST-enabled SoCs >>> >>>> >>>> Lack of MST support is not informative enough to claim it is not >>>> compatible with 8350. For example if it was working fine via fallback, >>>> then that statement is simply not correct. >>>> >>>> And it HAD to work fine, because there is nothing binding to >>>> qcom,sm6350-dp. >>> >>> It is working fine since currently we don't have MST support on the >>> driver side (nor do we describe MST clocks in DT). It's true that the >>> driver will have to handle non-MST DT for SM8350. However I definitely >>> don't want to describe both cases in the bindings. SM6350 is not going >>> to be compatible with the MST-enabled SM8350 schema. >> >> The question is rather: is SM6350 going to be compatible (working) with >> MST-enabled drivers. > > If somebody implements e.g. U-Boot DP MST support after we land DP MST > bindings, I would not guarantee that. SM8350 will already have second > stream clock. Having second stream clock does not mean device stops working with Linux kernel. I can easily imagine both cases after adding MST to the drivers, the SM6350 stops working or keeps working... Best regards, Krzysztof