linux-kernel - Re: [PATCH 03/15] dt-bindings: clock: qcom,dispcc-sm6125: Require GCC PLL0 DIV clock

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Date:   Mon, 26 Jun 2023 18:15:13 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Marijn Suijten <marijn.suijten@...ainline.org>,
        Konrad Dybcio <konrad.dybcio@...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 03/15] dt-bindings: clock: qcom,dispcc-sm6125: Require GCC
 PLL0 DIV clock

On 26/06/2023 16:26, Marijn Suijten wrote:
> On 2023-06-26 11:43:39, Konrad Dybcio wrote:
>> On 25.06.2023 21:48, Marijn Suijten wrote:
>>> On 2023-06-24 03:45:02, Konrad Dybcio wrote:
>>>> On 24.06.2023 02:41, Marijn Suijten wrote:
>>>>> The "gcc_disp_gpll0_div_clk_src" clock is consumed by the driver, will
>>>>> be passed from DT, and should be required by the bindings.
>>>>>
>>>>> Fixes: 8397c9c0c26b ("dt-bindings: clock: add QCOM SM6125 display clock bindings")
>>>>> Signed-off-by: Marijn Suijten <marijn.suijten@...ainline.org>
>>>>> ---
>>>> Ideally, you'd stick it at the bottom of the list, as the items: order
>>>> is part of the ABI
>>>
>>> This isn't an ABI break, as this driver nor its bindings require/declare
>>> a fixed order: they declare a relation between clocks and clock-names.
>> Bindings describe the ABI, drivers implement compliant code flow.
> 
> That is how bindings are supposed to be...  However typically the driver
> is written/ported first and then the bindings are simply created to

Your development process does not matter for the bindings. Whatever you
decide to do "typically" is your choice, although of course I understand
why you do it like that. You can argument the same that "I never create
bindings in my process, so the driver defines the ABI".

> reflect this, and sometimes (as is the case with this patch)
> incorrectly.
> 
> That, together with a lack of DTS and known-working device with it
> (which is why I'm submitting driver+bindings+dts in one series now!)
> makes us shoot ourselves in the foot by locking everyone into an ABI
> that makes no sense.

No one is locked into the ABI. SoC maintainer decides on this. However
unjustified ABI breaking or not caring about it at all is not the way to
go. It is not the correct process.

> 
>>> This orders the GCC clock just like other dispccs.  And the previous
>>> patch dropped the unused cfg_ahb_clk from the bindings, so all bets are
>>> off anyway.
>> Thinking about it again, the binding has not been consumed by any upstream
>> DT to date, so it should (tm) be fine to let it slide..
> 
> Exactly, I hope/doubt anyone was already using these incomplete
> bindings.  And again: the ABI here is the name->phandle mapping, the
> order Does Not Matter™.

No, it's not. Your one driver does not define the ABI. There are many
different drivers, many different operating systems and other software
components.

Best regards,
Krzysztof