linux-kernel - Re: [PATCH 1/3] arm64: dts: qcom: sdm630: fix UART1 pin bias

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Message-ID: <CAD=FV=WPrLNhJHhcutykGsE5rDCvxxPGcgqboWP6Oqs+Kw+M5Q@mail.gmail.com>
Date:   Mon, 3 Oct 2022 08:29:43 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.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 1/3] arm64: dts: qcom: sdm630: fix UART1 pin bias

Hi,

On Sat, Oct 1, 2022 at 2:58 AM Krzysztof Kozlowski
<krzysztof.kozlowski@...aro.org> wrote:
>
> > I would also note that convention on Qualcomm SoCs that I've worked on
> > was that bias shouldn't be specified in the SoC dtsi file and should
> > be left to board files. This is talked a bit about in a previous email
> > thread [1].
>
> Uh, that makes a lot of sense. It is almost always a property of a board.

Right, though it can make sense to have a "default" in the SoC
sometimes. For instance, for i2c you almost always want external
pullups so you can tune them to the speed/trace lengths. Thus having a
default in the SoC file to disable i2c pullups would make a lot of
sense. The problem is the ugly / non-obvious "delete-property" we need
to put in the board.dts file if we ever need to override the SoC's
pull. :(

I actually remember this not being a problem in Rockchip SoCs. I guess
it's because they end up having an extra level of indirection. I guess
there's no great way to do that for Qualcomm without changing the
bindings.


> > That being said, it does look like this was the intention of the
> > original commit, so thus:
> >
> > Reviewed-by: Douglas Anderson <dianders@...omium.org>
>
> Thanks.
>
> I can also drop the property entirely to match existing behavior (not
> the intention).

Hopefully someone who cares about this board can test and let you know
either way.


> > [1] https://lore.kernel.org/lkml/CAD=FV=VUL4GmjaibAMhKNdpEso_Hg_R=XeMaqah1LSj_9-Ce4Q@mail.gmail.com/