linux-kernel - Re: [PATCH 2/3] arm64: dts: qcom: sdm845-db845c: correct SPI2 pins drive strength

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Date:   Mon, 3 Oct 2022 19:57:44 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Doug Anderson <dianders@...omium.org>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Rob Clark <robdclark@...omium.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        "# 4.0+" <stable@...r.kernel.org>
Subject: Re: [PATCH 2/3] arm64: dts: qcom: sdm845-db845c: correct SPI2 pins
 drive strength

On 03/10/2022 17:40, Doug Anderson wrote:
>>>>
>>>> diff --git a/arch/arm64/boot/dts/qcom/sdm845-db845c.dts b/arch/arm64/boot/dts/qcom/sdm845-db845c.dts
>>>> index 132417e2d11e..a157eab66dee 100644
>>>> --- a/arch/arm64/boot/dts/qcom/sdm845-db845c.dts
>>>> +++ b/arch/arm64/boot/dts/qcom/sdm845-db845c.dts
>>>> @@ -1123,7 +1123,9 @@ &wifi {
>>>>
>>>>  /* PINCTRL - additions to nodes defined in sdm845.dtsi */
>>>>  &qup_spi2_default {
>>>> -       drive-strength = <16>;
>>>> +       pinmux {
>>>> +               drive-strength = <16>;
>>>> +       };
>>>
>>> The convention on Qualcomm boards of this era is that muxing (setting
>>> the function) is done under a "pinmux" node and, unless some of the
>>> pins need to be treated differently like for the UARTs, configuration
>>> (bias, drive strength, etc) is done under a "pinconf" subnode.
>>
>> Yes, although this was not expressed in bindings.
>>
>>> I
>>> believe that the "pinconf" subnode also needs to replicate the list of
>>> pins, or at least that's what we did everywhere else on sdm845 /
>>> sc7180.
>>
>> Yes.
>>
>>>
>>> Thus to match conventions, I assume you'd do:
>>>
>>> &qup_spi2_default {
>>>   pinconf {
>>
>> No, because I want a convention of all pinctrl bindings and drivers, not
>> convention of old pinctrl ones. The new ones are already moved or being
>> moved to "-state" and "-pins". In the same time I am also unifying the
>> requirement of "function" property - enforcing it in each node, thus
>> "pinconf" will not be valid anymore.
> 
> Regardless of where we want to end up, it feels like as of ${SUBJECT}
> patch this should match existing conventions in this file. If a later
> patch wants to change the conventions in this file then it can, but
> having just this one patch leaving things in an inconsistent state
> isn't great IMO...
> 
> If this really has to be one-off then the subnode shouldn't be called
> "pinmux". A subnode called "pinmux" implies that it just has muxing
> information in it. After your patch this is called "pinmux" but has
> _configuration_ in it.
> 

It is a poor argument to keep some convention which is both
undocumented, not kept in this file and known only to some folks
(although that's effect of lack of documentation). Even the bindings do
not say it should be "pinconf" but they mention "config" in example. The
existing sdm845.dts uses config - so why now there should be "pinconf"?
By this "convention" we have both "pinmux" and "mux", perfect. Several
other pins do not have pinmux/mux/config at all.

This convention was never implemented, so there is nothing to keep/match.

Changing it to "config" (because this is the most used "convention" in
the file and bindings) would also mean to add useless "pins" which will
be in next patch removed.

Best regards,
Krzysztof