mediatek: fix pwn fan settings for sinovoip bpi-r3 (v3)

backport upstream commit 095151b (mediatek: fix pwn fan settings for
sinovoip bpi-r3 (v3))

Popular cheap PWM fans for this machine, like the ones coming in
heatsink+fan combos will not work properly at the currently defined
medium speed. Trying different pwm setting using a command

  echo $value > /sys/devices/platform/pwm-fan/hwmon/hwmon1/pwm1

I found:

  pwm1 value     fan rotation speed   cpu temperature     notes
  -----------------------------------------------------------------
    0            maximal              31.5 Celsius        too noisy
   40            optimal              35.2 Celsius        no noise hearable
   95            minimal
   above 95      does not rotate      55.5 Celsius
  -----------------------------------------------------------------

Current cooling levels are:

	cooling-levels = <255 96 0>;

Thus only cpu-active-high and cpu-active-low modes are usable.
This patch fixes cpu-active-medium settings for bpi-r3 board.

This patch may not be enough. Users may wants to tweak their thermal_zone0
trip points, thus tuning fan rotation speed depending on cpu temperature.
That can be done on the base of the following example:

  === example =========
  # cpu temperature below 25 Celsius degrees, no rotation
  echo 25000 > /sys/class/thermal/thermal_zone0/trip_point_4_temp
  # cpu temperature in [25..32] Celsius degrees, normal rotation speed
  echo 32000 > /sys/class/thermal/thermal_zone0/trip_point_3_temp
  # cpu temperature above 50 Celsius degrees, max rotation speed
  echo 50000 > /sys/class/thermal/thermal_zone0/trip_point_2_temp
  =====================

Changes v2:
* put patch to a proper directory
* updated patch description
* tested with latest openwrt based on linux-6.6

Changes v3:
* use upstream linux patch
* update patch description

Signed-off-by: Mikhail Kshevetskiy <[email protected]>
Link: openwrt/openwrt#21252
Signed-off-by: Robert Marko <[email protected]>

Author: mkshevetskiy

target/linux/mediatek/patches-6.6/197-dts-mt7986a-bpi-r3-Change-fan-PWM-value.patch

@@ -0,0 +1,72 @@
+From 5f271fe1365b63f67fc384ca8d50d473d09de0d1 Mon Sep 17 00:00:00 2001
+From: Mikhail Kshevetskiy <[email protected]>
+Date: Tue, 3 Dec 2024 07:33:55 +0300
+Subject: [PATCH] arm64: dts: mediatek: mt7986-bpi-r3: Change fan PWM value for
+ mid speed
+
+Popular cheap PWM fans for this machine, like the ones coming in
+heatsink+fan combos will not work properly at the currently defined
+medium speed. Trying different pwm setting using a command
+
+  echo $value > /sys/devices/platform/pwm-fan/hwmon/hwmon1/pwm1
+
+I found:
+
+  pwm1 value     fan rotation speed   cpu temperature     notes
+  -----------------------------------------------------------------
+    0            maximal              31.5 Celsius        too noisy
+   40            optimal              35.2 Celsius        no noise hearable
+   95            minimal
+   above 95      does not rotate      55.5 Celsius
+  -----------------------------------------------------------------
+
+Thus only cpu-active-high and cpu-active-low modes are usable.
+I think this is wrong.
+
+This patch fixes cpu-active-medium settings for bpi-r3 board.
+
+I know, the patch is not ideal as it can break pwm fan for some users.
+Likely this is the only official mt7986-bpi-r3 heatsink+fan solution
+available on the market.
+
+This patch may not be enough. Users may wants to tweak their thermal_zone0
+trip points, thus tuning fan rotation speed depending on cpu temperature.
+That can be done on the base of the following example:
+
+  === example =========
+  # cpu temperature below 25 Celsius degrees, no rotation
+  echo 25000 > /sys/class/thermal/thermal_zone0/trip_point_4_temp
+  # cpu temperature in [25..32] Celsius degrees, normal rotation speed
+  echo 32000 > /sys/class/thermal/thermal_zone0/trip_point_3_temp
+  # cpu temperature above 50 Celsius degrees, max rotation speed
+  echo 50000 > /sys/class/thermal/thermal_zone0/trip_point_2_temp
+  =====================
+
+Signed-off-by: Mikhail Kshevetskiy <[email protected]>
+Acked-by: Frank Wunderlich <[email protected]>
+Reviewed-by: AngeloGioacchino Del Regno <[email protected]>
+
+---
+Changes from v1 to v2:
+ * improve patch description
+
+Changes from v2 to v3:
+ * added question to Frank Wunderlich
+
+Changes from v3 to v4:
+ * Acked by Frank Wunderlich
+---
+ arch/arm64/boot/dts/mediatek/mt7986a-bananapi-bpi-r3.dts | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+--- a/arch/arm64/boot/dts/mediatek/mt7986a-bananapi-bpi-r3.dts
++++ b/arch/arm64/boot/dts/mediatek/mt7986a-bananapi-bpi-r3.dts
+@@ -46,7 +46,7 @@
+ 		compatible = "pwm-fan";
+ 		#cooling-cells = <2>;
+ 		/* cooling level (0, 1, 2) - pwm inverted */
+-		cooling-levels = <255 96 0>;
++		cooling-levels = <255 40 0>;
+ 		pwms = <&pwm 0 10000>;
+ 		status = "okay";
+ 	};