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

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Date:   Fri, 30 Sep 2022 13:12:59 -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 2/3] arm64: dts: qcom: sdm845-db845c: correct SPI2 pins
 drive strength

Hi,

On Fri, Sep 30, 2022 at 11:22 AM Krzysztof Kozlowski
<krzysztof.kozlowski@...aro.org> wrote:
>
> The pin configuration (done with generic pin controller helpers and
> as expressed by bindings) requires children nodes with either:
> 1. "pins" property and the actual configuration,
> 2. another set of nodes with above point.
>
> The qup_spi2_default pin configuration used second method - with a
> "pinmux" child.
>
> Fixes: 8d23a0040475 ("arm64: dts: qcom: db845c: add Low speed expansion i2c and spi nodes")
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
>
> ---
>
> Not tested on hardware.
> ---
>  arch/arm64/boot/dts/qcom/sdm845-db845c.dts | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> 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. 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.

Thus to match conventions, I assume you'd do:

&qup_spi2_default {
  pinconf {
    pins = "gpio27", "gpio28", "gpio29", "gpio30";
    drive-strength = <16>;
  };
};

We've since moved away from this to a less cumbersome approach, but
for "older" boards like db845c we should probably match the existing
convention, or have a flag day and change all sdm845 boards over to
the new convention.

-Doug