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arm64: dts: mediatek: mt7986-bpi-r3: Change fan PWM value for mid speed

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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 <mikhail.kshevetskiy@iopsys.eu>
Acked-by: Frank Wunderlich <frank-w@public-files.de>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
This commit is contained in:
Mikhail Kshevetskiy 2025-09-30 05:16:56 +03:00 committed by AngeloGioacchino Del Regno
parent bbfb1118fe
commit 8365a3e1fd
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GPG Key ID: 9A3604CFAD978478
1 changed files with 1 additions and 1 deletions
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arch/arm64/boot/dts/mediatek/mt7986a-bananapi-bpi-r3.dts
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@ -42,7 +42,7 @@ fan: pwm-fan {
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";
};