linux-kernel - Re: [PATCH 1/7] arm64: dts: qcom: sc8280xp: remove GCC from CX power domain

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Message-ID: <CAJB8c06F8MaDWEgNOVgL51NG3vgnxcuC2ta2UpbyrG2BqcOVfQ@mail.gmail.com>
Date:   Sat, 31 Dec 2022 11:04:30 +0000
From:   "Bryan O'Donoghue" <pure.logic@...us-software.ie>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/7] arm64: dts: qcom: sc8280xp: remove GCC from CX power domain

On Fri, Dec 30, 2022 at 4:04 PM Krzysztof Kozlowski
<krzysztof.kozlowski@...aro.org> wrote:
>
> Bindings do not allow power-domain property in GCC clock controller and
> documentation does not indicate that GCC is part of VDD_CX.
>
> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
>
> ---
>
> Maybe the bindings should be fixed? Maybe this was added as workaround?
> Anyway looking at documentation I do not see such relation, except
> downstream vdd_cx-supply (which is the same as in other SoCs and we do
> not represent it in upstream).
> ---
>  arch/arm64/boot/dts/qcom/sc8280xp.dtsi | 1 -
>  1 file changed, 1 deletion(-)
>
> diff --git a/arch/arm64/boot/dts/qcom/sc8280xp.dtsi b/arch/arm64/boot/dts/qcom/sc8280xp.dtsi
> index 1d1420c8720c..d14663c9f34c 100644
> --- a/arch/arm64/boot/dts/qcom/sc8280xp.dtsi
> +++ b/arch/arm64/boot/dts/qcom/sc8280xp.dtsi
> @@ -799,7 +799,6 @@ gcc: clock-controller@...000 {
>                                  <&pcie4_phy>,
>                                  <0>,
>                                  <0>;
> -                       power-domains = <&rpmhpd SC8280XP_CX>;
>                 };
>
>                 ipcc: mailbox@...000 {
> --
> 2.34.1
>

You'd be better off adding the documentation. The CX rail is required
to power the clock controller.
If you are pulling this out and finding nothing breaks, its probably
because the bootloader left it on.

Per my understanding of what dts is though, we ought to be
representing the hardware dependency.

gcc is a root clock for just about every peripheral so, you can be
sure it is on when you boot.

Seems to me as if the right thing to do is to retain the dts and
update the documentation.

---
bod