Now the new kernel has used pwm-fan kernel driver to deal with the fan control, so the old pwm fan scripts won’t work. Here is a guide on how to customize your onw pwm fan curve since different cases/environment/fans need different fan curve.
I will take armbian’s kernel as example because I use armbian as my daily use os. But it will be similar if you’re using official radxa’s kernel, radxa’s kernel uses different cooling levels.
If you take a look at the devicetree of rock5b, there is a node fan0 with this property:
cooling-levels = <72 94 117 139 162 184 207 229 255>;
This property works togather with property trips defined in node soc_thermal
Here is the default pwm fan curve defined in armbian’s kernel devicetree:
| cooling level value | trip temp defined in device tree | working temperature |
|---|---|---|
| 72 | temp < 45 | |
| 94 | 45 | 45-50 |
| 117 | 50 | 50-55 |
| 139 | 55 | 55-60 |
| 162 | 60 | 60-65 |
| 184 | 65 | 65-70 |
| 207 | 70 | 70-75 |
| 229 | 75 | 75-80 |
| 255 | 80 | temp > 80 |
Cooling level vaule ranges from 0 to 255, which is the pwm value of the fan. It doesn’t start from 0 in the devicetree because I want the fan keeps spinning at its lowest speed so that I can get a stable temperature when it’s idle.
So we need another 9 pwm values like 72 94 117 139 162 184 207 229 255 for our own fan. Here is how to do it:
- Login to root, and set the thermal policy to
user_space:
echo user_space > /sys/class/thermal/thermal_zone0/policy
- Then you can set the fan speed by setting pwm value, for example, if you want to set the speed to max, just set it to 255:
echo 255 > /sys/devices/platform/pwm-fan/hwmon/hwmon8/pwm1
- Find the miminal pwm value that makes the fan spinning. I set the default value to 72 because it’s the minimal value of my fan.
- After you get your minimal pwm value, let’s make it 120 as an example, we just have to fill the other 7 values between 120 and 255, like
120 135 150 165 180 195 210 235 255 - Then create a devicetree overlay to set the new pwm fan curve:
/dts-v1/;
/plugin/;
/ {
fragment@0 {
target = <&fan0>;
__overlay__ {
cooling-levels = <120 135 150 165 180 195 210 235 255>;
};
};
};
- If you save the devicetree overlay as filename
pwm-fan.dts, then use the following command to apply it:
sudo armbian-add-overlay pwm-fan.dts
- Then reboot to see if it is applied. Make sure you’re using
step_wisefor your thermal_zone0:
$ cat /sys/class/thermal/thermal_zone0/policy
step_wise
- And check if your pwm value changes with temperature:
watch -n1 cat /sys/devices/platform/pwm-fan/hwmon/hwmon8/pwm1 /sys/class/thermal/thermal_zone0/temp