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

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Message-ID: <950f3844-ed7e-4f18-9a27-f06c7947af02@linaro.org>
Date:   Tue, 4 Oct 2022 08:46:55 +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 1/3] arm64: dts: qcom: sdm630: fix UART1 pin bias

On 03/10/2022 17:29, Doug Anderson wrote:
> 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. 

If the default is safe, then could be. But it is still causing a risk of
developer just forgetting to configure the configs for his board.
Bringup of DTS should be a conscious decision, not just "copy and hope
it works", therefore recommendation is to configure per-board properties
in board. Even if it means duplication. The same was for board-provided
clocks or aliases.

> 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. :(

Which might not help in reducing amount of code...



Best regards,
Krzysztof