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From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@collabora.com>
To:     robh+dt@kernel.org
Cc:     krzysztof.kozlowski+dt@linaro.org, matthias.bgg@gmail.com,
        tinghan.shen@mediatek.com, seiya.wang@mediatek.com,
        angelogioacchino.delregno@collabora.com,
        devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: [PATCH] arm64: dts: mediatek: mt8195: Fix CPUs capacity-dmips-mhz
Date:   Wed,  5 Oct 2022 11:34:03 +0200
Message-Id: <20221005093404.33102-1-angelogioacchino.delregno@collabora.com>
MIME-Version: 1.0
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The capacity-dmips-mhz parameter was miscalculated: this SoC runs
the first (Cortex-A55) cluster at a maximum of 2000MHz and the
second (Cortex-A78) cluster at a maximum of 3000MHz.

In order to calculate the right capacity-dmips-mhz, the following
test was performed:
1. CPUFREQ governor was set to 'performance' on both clusters
2. Ran dhrystone with 500000000 iterations for 10 times on each cluster
3. Calculate the mean result for each cluster
4. Calculate DMIPS/MHz: dmips_mhz = dmips_per_second / cpu_mhz
5. Scale results to 1024:
   result_c0 = (dmips_mhz_c0 - min_dmips_mhz(c0, c1)) /
               (max_dmips_mhz(c0, c1) - min_dmips_mhz(c0, c1)) * 1024

The mean results for this SoC are:
Cluster 0 (LITTLE): 11990400 Dhry/s
Cluster 1 (BIG): 59809036 Dhry/s

The calculated scaled results are:
Cluster 0: 307,934312801831 (rounded to 308)
Cluster 1: 1024

Fixes: 37f2582883be ("arm64: dts: Add mediatek SoC mt8195 and evaluation board")
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
---
 arch/arm64/boot/dts/mediatek/mt8195.dtsi | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/boot/dts/mediatek/mt8195.dtsi b/arch/arm64/boot/dts/mediatek/mt8195.dtsi
index 905d1a90b406..0b85b5874a4f 100644
--- a/arch/arm64/boot/dts/mediatek/mt8195.dtsi
+++ b/arch/arm64/boot/dts/mediatek/mt8195.dtsi
@@ -36,7 +36,7 @@ cpu0: cpu@0 {
 			enable-method = "psci";
 			performance-domains = <&performance 0>;
 			clock-frequency = <1701000000>;
-			capacity-dmips-mhz = <578>;
+			capacity-dmips-mhz = <308>;
 			cpu-idle-states = <&cpu_off_l &cluster_off_l>;
 			next-level-cache = <&l2_0>;
 			#cooling-cells = <2>;
@@ -49,7 +49,7 @@ cpu1: cpu@100 {
 			enable-method = "psci";
 			performance-domains = <&performance 0>;
 			clock-frequency = <1701000000>;
-			capacity-dmips-mhz = <578>;
+			capacity-dmips-mhz = <308>;
 			cpu-idle-states = <&cpu_off_l &cluster_off_l>;
 			next-level-cache = <&l2_0>;
 			#cooling-cells = <2>;
@@ -62,7 +62,7 @@ cpu2: cpu@200 {
 			enable-method = "psci";
 			performance-domains = <&performance 0>;
 			clock-frequency = <1701000000>;
-			capacity-dmips-mhz = <578>;
+			capacity-dmips-mhz = <308>;
 			cpu-idle-states = <&cpu_off_l &cluster_off_l>;
 			next-level-cache = <&l2_0>;
 			#cooling-cells = <2>;
@@ -75,7 +75,7 @@ cpu3: cpu@300 {
 			enable-method = "psci";
 			performance-domains = <&performance 0>;
 			clock-frequency = <1701000000>;
-			capacity-dmips-mhz = <578>;
+			capacity-dmips-mhz = <308>;
 			cpu-idle-states = <&cpu_off_l &cluster_off_l>;
 			next-level-cache = <&l2_0>;
 			#cooling-cells = <2>;
-- 
2.37.2