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

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Message-ID: <1808f43b-5a76-d4e6-a36d-88779ecd3836@linaro.org>
Date:   Tue, 27 Jun 2023 00:46:28 +0200
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Marijn Suijten <marijn.suijten@...ainline.org>
Cc:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        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 22:28, Marijn Suijten wrote:
> On 2023-06-26 20:57:51, Konrad Dybcio wrote:
>> 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 
> 
> (Looks like I forgot to complete this sentence before sending,
> apologies)
> 
>> 6375 needs the throttle clk and the clock(-names) are strongly ordered
>> so having minItems: 6 discards the last entry
> 
> The question is whether or not we should have maxItems: 6 to disallow
> the clock from being passed: right now it is optional and either is
> allowed for any !6375 SoC.
That's a very good question. I don't have a 7180 to test, but for
you it seems to cause inexplicable issues on 6125..

Konrad
> 
> - Marijn
> 
>>
>> 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