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@xxxxxxxxx>
---
Changes from v1 to v2:
* improve patch description
---
arch/arm64/boot/dts/mediatek/mt7986a-bananapi-bpi-r3.dts | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
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 ed79ad1ae871..b0cc0cbdff0f 100644
--- 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 @@ 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";
};
--
2.47.2
