linux-kernel - Re: [PATCH v2 01/31] arm64: dts: qcom: msm8916: correct sleep clock frequency

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Message-ID: <Z0rnRC_BqgkE3w1P@gerhold.net>
Date: Sat, 30 Nov 2024 11:21:56 +0100
From: Stephan Gerhold <stephan@...hold.net>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc: Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konradybcio@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, Leo Yan <leo.yan@...ux.dev>,
	Joseph Gates <jgates@...areup.com>,
	Georgi Djakov <djakov@...nel.org>, Shawn Guo <shawn.guo@...aro.org>,
	Zac Crosby <zac@...areup.com>,
	Bastian Köcher <git@...r.de>,
	Andy Gross <andy.gross@...aro.org>,
	Jeremy McNicoll <jeremymc@...hat.com>,
	Rohit Agarwal <quic_rohiagar@...cinc.com>,
	Melody Olvera <quic_molvera@...cinc.com>,
	Bhupesh Sharma <bhupesh.sharma@...aro.org>,
	cros-qcom-dts-watchers@...omium.org,
	Stephen Boyd <swboyd@...omium.org>,
	Rajendra Nayak <quic_rjendra@...cinc.com>,
	Martin Botka <martin.botka@...ainline.org>,
	Jonathan Marek <jonathan@...ek.ca>, Vinod Koul <vkoul@...nel.org>,
	Tengfei Fan <quic_tengfan@...cinc.com>,
	Fenglin Wu <quic_fenglinw@...cinc.com>,
	Neil Armstrong <neil.armstrong@...aro.org>,
	Abel Vesa <abel.vesa@...aro.org>,
	Alexandru Marc Serdeliuc <serdeliuk@...oo.com>,
	Vladimir Zapolskiy <vladimir.zapolskiy@...aro.org>,
	Sibi Sankar <quic_sibis@...cinc.com>,
	Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
	Jun Nie <jun.nie@...aro.org>, James Willcox <jwillcox@...areup.com>,
	Max Chen <mchen@...areup.com>,
	Vincent Knecht <vincent.knecht@...loo.org>,
	Benjamin Li <benl@...areup.com>,
	Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
	linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Stephan Gerhold <stephan.gerhold@...aro.org>
Subject: Re: [PATCH v2 01/31] arm64: dts: qcom: msm8916: correct sleep clock
 frequency

On Sat, Nov 30, 2024 at 03:44:13AM +0200, Dmitry Baryshkov wrote:
>The MSM8916 platform uses PM8916 to provide sleep clock. According to the
>documentation, that clock has 32.7645 kHz frequency. Correct the sleep
>clock definition.
>
>Fixes: f4fb6aeafaaa ("arm64: dts: qcom: msm8916: Add fixed rate on-board oscillators")
>Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>

Thanks for spotting this! This fix looks good independent of the more
controversial "arm64: dts: qcom: move board clocks to SoC DTSI files"
changes. Maybe move these to a separate series?

>---
> arch/arm64/boot/dts/qcom/msm8916.dtsi | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
>diff --git a/arch/arm64/boot/dts/qcom/msm8916.dtsi b/arch/arm64/boot/dts/qcom/msm8916.dtsi
>index 5e558bcc9d87893486352e5e211f131d4a1f67e5..8f35c9af18782aa1da7089988692e6588c4b7c5d 100644
>--- a/arch/arm64/boot/dts/qcom/msm8916.dtsi
>+++ b/arch/arm64/boot/dts/qcom/msm8916.dtsi
>@@ -125,7 +125,7 @@ xo_board: xo-board {
> 		sleep_clk: sleep-clk {
> 			compatible = "fixed-clock";
> 			#clock-cells = <0>;
>-			clock-frequency = <32768>;
>+			clock-frequency = <32764>;

To be precise the PM8916 specification says the sleep clock is "The 19.2
MHz XO divided by 586". Maybe we can actually describe it that way with
a fixed-factor-clock?

		sleep_clk: sleep-clk {
			compatible = "fixed-factor-clock";
			clocks = <&xo_board>;
			#clock-cells = <0>;
			clock-div = <586>;
			clock-mult = <1>;
		};

If we keep the fixed-clock with the hardcoded frequency I wonder if we
should put 32765 instead of 32764. If you calculate it exactly it's
slightly closer to 32765 than 32764. :-)

	19200000/586 = 32764.505119453926 = ~32765

Thanks,
Stephan