linux-kernel - Re: [PATCH v2 1/1] arm64: dts: rockchip: rk3528: Add CPU frequency scaling support

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Message-ID: <5025631.aeNJFYEL58@phil>
Date: Thu, 10 Jul 2025 13:45:43 +0200
From: Heiko Stuebner <heiko@...ech.de>
To: Chukun Pan <amadeus@....edu.cn>
Cc: Yao Zi <ziyao@...root.org>, Rob Herring <robh@...nel.org>,
 Chukun Pan <amadeus@....edu.cn>, Jonas Karlman <jonas@...boo.se>,
 Conor Dooley <conor+dt@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 linux-arm-kernel@...ts.infradead.org, linux-rockchip@...ts.infradead.org,
 linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject:
 Re: [PATCH v2 1/1] arm64: dts: rockchip: rk3528: Add CPU frequency scaling
 support

Am Freitag, 20. Juni 2025, 12:00:10 Mitteleuropäische Sommerzeit schrieb Chukun Pan:
> By default, the CPUs on RK3528 operates at 1.5GHz. Add CPU frequency and
> voltage mapping to the device tree to enable dynamic scaling via cpufreq.
> 
> The OPP values come from downstream kernel[1]. Both 408MHz and 600MHz
> frequencies use the normal PLL, so use the corresponding highest voltage.
> 
> The voltage used for other frequencies can't be less than above (875mV).
> Therefore, 816MHz to 1200MHz also uses the corresponding highest voltage.

There has often been the argument that selecting a frequency that has the
same voltage as a faster frequency does not save any power.

Hence I remember that we dropped slower frequencies on other socs
that share the same voltage with a higher frequency.

> 
> The remaining 1416MHz to 2016MHz use a voltage close to actual frequency.
> 
> [1] https://github.com/rockchip-linux/kernel/blob/develop-5.10/arch/arm64/boot/dts/rockchip/rk3528.dtsi
> 
> Signed-off-by: Chukun Pan <amadeus@....edu.cn>
> ---
>  arch/arm64/boot/dts/rockchip/rk3528.dtsi | 64 ++++++++++++++++++++++++
>  1 file changed, 64 insertions(+)
> 
> diff --git a/arch/arm64/boot/dts/rockchip/rk3528.dtsi b/arch/arm64/boot/dts/rockchip/rk3528.dtsi
> index 829f980ea353..5cb7f10b79ed 100644
> --- a/arch/arm64/boot/dts/rockchip/rk3528.dtsi
> +++ b/arch/arm64/boot/dts/rockchip/rk3528.dtsi
> @@ -53,6 +53,7 @@ cpu0: cpu@0 {
>  			device_type = "cpu";
>  			enable-method = "psci";
>  			clocks = <&scmi_clk SCMI_CLK_CPU>;
> +			operating-points-v2 = <&cpu_opp_table>;
>  		};
>  
>  		cpu1: cpu@1 {
> @@ -61,6 +62,7 @@ cpu1: cpu@1 {
>  			device_type = "cpu";
>  			enable-method = "psci";
>  			clocks = <&scmi_clk SCMI_CLK_CPU>;
> +			operating-points-v2 = <&cpu_opp_table>;
>  		};
>  
>  		cpu2: cpu@2 {
> @@ -69,6 +71,7 @@ cpu2: cpu@2 {
>  			device_type = "cpu";
>  			enable-method = "psci";
>  			clocks = <&scmi_clk SCMI_CLK_CPU>;
> +			operating-points-v2 = <&cpu_opp_table>;
>  		};
>  
>  		cpu3: cpu@3 {
> @@ -77,6 +80,67 @@ cpu3: cpu@3 {
>  			device_type = "cpu";
>  			enable-method = "psci";
>  			clocks = <&scmi_clk SCMI_CLK_CPU>;
> +			operating-points-v2 = <&cpu_opp_table>;
> +		};
> +	};
> +
> +	cpu_opp_table: opp-table-cpu {
> +		compatible = "operating-points-v2";
> +		opp-shared;
> +
> +		opp-408000000 {
> +			opp-hz = /bits/ 64 <408000000>;
> +			opp-microvolt = <875000 875000 1100000>;
> +			clock-latency-ns = <40000>;
> +			opp-suspend;
> +		};
> +
> +		opp-600000000 {
> +			opp-hz = /bits/ 64 <600000000>;
> +			opp-microvolt = <875000 875000 1100000>;
> +			clock-latency-ns = <40000>;
> +		};
> +
> +		opp-816000000 {
> +			opp-hz = /bits/ 64 <816000000>;
> +			opp-microvolt = <875000 875000 1100000>;
> +			clock-latency-ns = <40000>;
> +		};
> +
> +		opp-1008000000 {
> +			opp-hz = /bits/ 64 <1008000000>;
> +			opp-microvolt = <875000 875000 1100000>;
> +			clock-latency-ns = <40000>;
> +		};
> +
> +		opp-1200000000 {
> +			opp-hz = /bits/ 64 <1200000000>;
> +			opp-microvolt = <900000 900000 1100000>;
> +			clock-latency-ns = <40000>;
> +		};
> +
> +		opp-1416000000 {
> +			opp-hz = /bits/ 64 <1416000000>;
> +			opp-microvolt = <925000 925000 1100000>;
> +			clock-latency-ns = <40000>;
> +		};
> +
> +		opp-1608000000 {
> +			opp-hz = /bits/ 64 <1608000000>;
> +			opp-microvolt = <975000 975000 1100000>;
> +			clock-latency-ns = <40000>;
> +		};
> +
> +		opp-1800000000 {
> +			opp-hz = /bits/ 64 <1800000000>;
> +			opp-microvolt = <1037500 1037500 1100000>;
> +			clock-latency-ns = <40000>;
> +		};
> +
> +		opp-2016000000 {
> +			opp-hz = /bits/ 64 <2016000000>;
> +			opp-microvolt = <1100000 1100000 1100000>;
> +			clock-latency-ns = <40000>;
>  		};
>  	};
>  
>