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

[Stephan Gerhold <stephan@gerhold.net>]

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@linaro.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