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

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Date:   Mon, 26 Jun 2023 22:28:41 +0200
From:   Marijn Suijten <marijn.suijten@...ainline.org>
To:     Konrad Dybcio <konrad.dybcio@...aro.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 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.

- 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