linux-kernel - [PATCH] ARM: dts: rockchip: Add dynamic-power-coefficient for rk3288

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Date:   Thu, 11 Apr 2019 17:01:58 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Heiko Stuebner <heiko@...ech.de>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Douglas Anderson <dianders@...omium.org>,
        Matthias Kaehlcke <mka@...omium.org>
Subject: [PATCH] ARM: dts: rockchip: Add dynamic-power-coefficient for rk3288

The value was determined with the following method:

- take CPUs 1-3 offline
- for each OPP
  - set cpufreq min and max freq to OPP freq
  - start dhrystone benchmark
  - measure CPU power consumption during 10s
  - calculate Cx for OPPx
    - Cx = (Px - P1) / (Vx²fx - V1²f1)          [1]
      using the following units: mW / Ghz / V   [2]
- C = avg(C2, ..., Cn)

[1] see commit 4daa001a1773 ("arm64: dts: juno: Add cpu
     dynamic-power-coefficient information")
[2] https://patchwork.kernel.org/patch/10493615/#22158551

FTR, these are the values for the different OPPs:

freq (kHz)   	mV		Px (mW)		Cx

126000		900		39
216000		900		66		370
312000		900		95		372
408000		900		122		363
600000		900		177		359
696000		950		230		363
816000		1000		297		361
1008000		1050		404		362
1200000		1100		528		362
1416000		1200		770		377
1512000		1300		984		385
1608000		1350		1156		394

Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
---
I couldn't find any really comprehensive information on determining
the dynamic-power-coefficient, the method used is my understanding
mostly derived from the sources mentioned above, the resulting value
is within a reasonable range and the range of the intermediate Cx
values is consistent. If someone knows better and things should be
done differently please share your knowledge :)
---
 arch/arm/boot/dts/rk3288.dtsi | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/arm/boot/dts/rk3288.dtsi b/arch/arm/boot/dts/rk3288.dtsi
index 23e9c5253019..f0d92b045c57 100644
--- a/arch/arm/boot/dts/rk3288.dtsi
+++ b/arch/arm/boot/dts/rk3288.dtsi
@@ -61,6 +61,7 @@
 			reg = <0x500>;
 			resets = <&cru SRST_CORE0>;
 			operating-points-v2 = <&cpu_opp_table>;
+			dynamic-power-coefficient = <370>;
 			#cooling-cells = <2>; /* min followed by max */
 			clock-latency = <40000>;
 			clocks = <&cru ARMCLK>;
@@ -71,6 +72,7 @@
 			reg = <0x501>;
 			resets = <&cru SRST_CORE1>;
 			operating-points = <&cpu_opp_table>;
+			dynamic-power-coefficient = <370>;
 			#cooling-cells = <2>; /* min followed by max */
 			clock-latency = <40000>;
 			clocks = <&cru ARMCLK>;
@@ -81,6 +83,7 @@
 			reg = <0x502>;
 			resets = <&cru SRST_CORE2>;
 			operating-points = <&cpu_opp_table>;
+			dynamic-power-coefficient = <370>;
 			#cooling-cells = <2>; /* min followed by max */
 			clock-latency = <40000>;
 			clocks = <&cru ARMCLK>;
@@ -91,6 +94,7 @@
 			reg = <0x503>;
 			resets = <&cru SRST_CORE3>;
 			operating-points = <&cpu_opp_table>;
+			dynamic-power-coefficient = <370>;
 			#cooling-cells = <2>; /* min followed by max */
 			clock-latency = <40000>;
 			clocks = <&cru ARMCLK>;
-- 
2.21.0.392.gf8f6787159e-goog