/sys/class/hwmon/hwmonX/pwm1 missing after upgrading to 20.04

Question

I have an Asus ux360ua that is a good laptop but it's fan noise is quite loud and unpleasant. Unfortunately, the automatic control of the fan is also very aggressive and make it work at a quite high speed even if the cpu is cold (e.g. 3500 rpm at only 40°C...). I ended up writing a little deamon-like program that monitor the cpu temps and write in the file /sys/class/hwmon/hwmonX/pwm1 which control the fan speed.

Now my problem: I upgraded to 20.04 from 19.10 and surprise, this file do not exist anymore!

What I tried:

• Update the bios to the newest version: no effects.
• Reboot with the previous kernel (5.3 instead of 5.4) and the file /sys/class/hwmon/hwmonX/pwm1 came back.

Here is the return of dmesg | grep asus when booting with the kernel 5.3

dmesg | grep asus
[    3.729322] asus_wmi: ASUS WMI generic driver loaded
[    3.775279] asus_wmi: Initialization: 0x1
[    3.775352] asus_wmi: BIOS WMI version: 7.9
[    3.775429] asus_wmi: SFUN value: 0xa0065
[    3.775432] asus-nb-wmi asus-nb-wmi: Detected ATK, not ASUSWMI, use DSTS
[    3.775434] asus-nb-wmi asus-nb-wmi: Detected ATK, enable event queue
[    3.778639] input: Asus WMI hotkeys as /devices/platform/asus-nb-wmi/input/input25
[    3.791560] asus_wmi: Number of fans: 1

Here is the return of dmesg | grep asus when booting with the kernel 5.4

dmesg | grep asus
[    3.716565] asus_wmi: ASUS WMI generic driver loaded
[    3.747409] asus_wmi: Initialization: 0x1
[    3.747472] asus_wmi: BIOS WMI version: 7.9
[    3.747542] asus_wmi: SFUN value: 0xa0065
[    3.747544] asus-nb-wmi asus-nb-wmi: Detected ATK, not ASUSWMI, use DSTS
[    3.747546] asus-nb-wmi asus-nb-wmi: Detected ATK, enable event queue
[    3.750808] input: Asus WMI hotkeys as /devices/platform/asus-nb-wmi/input/input25

I'd really appreciate any suggestions, I'm currently sticking to the 5.3 as a short term solution because this useless fan noise drive me crazy... Many thanks!

Answer 1

I ended up using NBFC to control the fan.

For comparison with the previous method:

• Only 6 level vs 205
• No quiet ventilation is possible: the slowest level is noisy, so its either passive either noisy.
• maximum speed is about 70 % of the real maximum

The performance are worse than my previous configuration but the big and absolute advantage is that it works with newer kernels