linux-kernel - Re: [PATCH RFC 24/24] arm64: dts: qcom: x1e80100: Describe GPU

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Message-ID: <aIevIuMDA5R8igmi@linaro.org>
Date: Mon, 28 Jul 2025 19:10:58 +0200
From: Stephan Gerhold <stephan.gerhold@...aro.org>
To: Konrad Dybcio <konradybcio@...nel.org>
Cc: Ulf Hansson <ulf.hansson@...aro.org>,
	Johan Hovold <johan+linaro@...nel.org>,
	Bjorn Andersson <andersson@...nel.org>,
	Taniya Das <taniya.das@....qualcomm.com>,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...nel.org>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Taniya Das <quic_tdas@...cinc.com>,
	Imran Shaik <quic_imrashai@...cinc.com>,
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
	Dmitry Baryshkov <lumag@...nel.org>,
	cros-qcom-dts-watchers@...omium.org,
	Douglas Anderson <dianders@...omium.org>,
	Vinod Koul <vkoul@...nel.org>,
	Richard Acayan <mailingradian@...il.com>,
	Andy Gross <andy.gross@...aro.org>,
	Ajit Pandey <quic_ajipan@...cinc.com>,
	Luca Weiss <luca.weiss@...rphone.com>,
	Jonathan Marek <jonathan@...ek.ca>,
	Neil Armstrong <neil.armstrong@...aro.org>,
	Jagadeesh Kona <quic_jkona@...cinc.com>,
	Akhil P Oommen <akhilpo@....qualcomm.com>,
	Marijn Suijten <marijn.suijten@...ainline.org>,
	linux-arm-msm@...r.kernel.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-clk@...r.kernel.org,
	devicetree@...r.kernel.org,
	Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
	Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Subject: Re: [PATCH RFC 24/24] arm64: dts: qcom: x1e80100: Describe GPU_CC
 power plumbing requirements

On Mon, Jul 28, 2025 at 06:16:24PM +0200, Konrad Dybcio wrote:
> From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
> 
> A number of power rails must be powered on in order for GPU_CC to
> function. Ensure that's conveyed to the OS.
> 
> Fixes: 721e38301b79 ("arm64: dts: qcom: x1e80100: Add gpu support")
> Signed-off-by: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
> ---
>  arch/arm64/boot/dts/qcom/x1e80100.dtsi | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/arch/arm64/boot/dts/qcom/x1e80100.dtsi b/arch/arm64/boot/dts/qcom/x1e80100.dtsi
> index 5e9a8fa3cf96468b12775f91192cbd779d5ce946..6620517fbb0f3ed715c4901ec53dcbc6235be88f 100644
> --- a/arch/arm64/boot/dts/qcom/x1e80100.dtsi
> +++ b/arch/arm64/boot/dts/qcom/x1e80100.dtsi
> @@ -3928,6 +3928,12 @@ gpucc: clock-controller@...0000 {
>  			clocks = <&bi_tcxo_div2>,
>  				 <&gcc GCC_GPU_GPLL0_CPH_CLK_SRC>,
>  				 <&gcc GCC_GPU_GPLL0_DIV_CPH_CLK_SRC>;
> +
> +			power-domains = <&rpmhpd RPMHPD_CX>,
> +					<&rpmhpd RPMHPD_MX>,
> +					<&rpmhpd RPMHPD_GFX>,
> +					<&rpmhpd RPMHPD_GMXC>;
> +
>  			#clock-cells = <1>;
>  			#reset-cells = <1>;
>  			#power-domain-cells = <1>;
> 

To repeat your own message from a couple of months back [1]:

> You shouldn't be messing with VDD_GFX on platforms with a GMU.
>
> Parts of the clock controller are backed by one of the MX rails,
> with some logic depending on CX/GFX, but handling of the latter is
> fully deferred to the GMU firmware.
>
> Konrad

Please describe somewhere in the cover letter or the individual patches
how this relates to the responsibilities of the GMU. I searched for
"GMU" in the patch series and couldn't find any note about this.

Also: How much is a plain "power on" votes (without a corresponding
"required-opps") really worth nowadays? An arbitrary low voltage level
on those rails won't be sufficient to make the GPU_CC actually
"function". Do you need "required-opps" here? In the videocc/camcc case
we have those.

Thanks,
Stephan

[1]: https://lore.kernel.org/linux-arm-msm/2dae7d88-4b3e-452f-9555-05f10b42dabc@oss.qualcomm.com/