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 <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>

diff --git a/arch/arm64/boot/dts/mediatek/mt7986a-bananapi-bpi-r3.dts b/arch/arm64/boot/dts/mediatek/mt7986a-bananapi-bpi-r3.dts
index e7654dc9a1c9b4ddaa3d296a86ed3f1909c916df..19f538d160ab5f9d0484ce6ef5c355f564c80dcd 100644 (file)
--- a/arch/arm64/boot/dts/mediatek/mt7986a-bananapi-bpi-r3.dts
+++ b/arch/arm64/boot/dts/mediatek/mt7986a-bananapi-bpi-r3.dts
@@ -42,7 +42,7 @@
                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";
        };