linux-kernel - Re: [PATCH 06/15] dt-bindings: display/msm: sc7180-dpu: Describe SM6125

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Date:   Mon, 26 Jun 2023 20:57:51 +0200
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Marijn Suijten <marijn.suijten@...ainline.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Krishna Manikandan <quic_mkrishn@...cinc.com>,
        ~postmarketos/upstreaming@...ts.sr.ht,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Martin Botka <martin.botka@...ainline.org>,
        Jami Kettunen <jami.kettunen@...ainline.org>,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Krzysztof Kozlowski <krzk@...nel.org>,
        linux-clk@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, Lux Aliaga <they@...t.lgbt>
Subject: Re: [PATCH 06/15] dt-bindings: display/msm: sc7180-dpu: Describe
 SM6125

On 26.06.2023 19:54, Marijn Suijten wrote:
> On 2023-06-26 18:16:58, Krzysztof Kozlowski wrote:
>> On 25/06/2023 21:52, Marijn Suijten wrote:
>>> On 2023-06-24 11:12:52, Krzysztof Kozlowski wrote:
>>>> On 24/06/2023 02:41, Marijn Suijten wrote:
>>>>> SM6125 is identical to SM6375 except that while downstream also defines
>>>>> a throttle clock, its presence results in timeouts whereas SM6375
>>>>> requires it to not observe any timeouts.
>>>>
>>>> Then it should not be allowed, so you need either "else:" block or
>>>> another "if: properties: compatible:" to disallow it. Because in current
>>>> patch it would be allowed.
>>>
>>> That means this binding is wrong/incomplete for all other SoCs then.
>>> clock(-name)s has 6 items, and sets `minItems: 6`.  Only for sm6375-dpu
> 
> Of course meant to say that clock(-name)s has **7** items, not 6.
> 
>>> does it set `minItems: 7`, but an else case is missing.
>>
>> Ask the author why it is done like this.
> 
> Konrad, can you clarify why other 
6375 needs the throttle clk and the clock(-names) are strongly ordered
so having minItems: 6 discards the last entry

Konrad
> 
>>> Shall I send a Fixes: ed41005f5b7c ("dt-bindings: display/msm:
>>> sc7180-dpu: Describe SM6350 and SM6375") for that, and should maxItems:
>>> 6 be the default under clock(-name)s or in an else:?
>>
>> There is no bug to fix. Or at least it is not yet known. Whether other
>> devices should be constrained as well - sure, sounds reasonable, but I
>> did not check the code exactly.
> 
> I don't know either, but we need this information to decide whether to
> use `maxItems: 6`:
> 
> 1. Directly on the property;
> 2. In an `else:` case on the current `if: sm6375-dpu` (should have the
>    same effect as 1., afaik);
> 3. In a second `if:` case that lists all SoCS explicitly.
> 
> Since we don't have this information, I think option 3. is the right way
> to go, setting `maxItems: 6` for qcom,sm6125-dpu.
> 
> However, it is not yet understood why downstream is able to use the
> throttle clock without repercussions.
> 
>> We talk here about this patch.
> 
> We used this patch to discover that other SoCs are similarly
> unconstrained.  But if you don't want me to look into it, by all means!
> Saves me a lot of time.  So I will go with option 3.
> 
> - Marijn