# /etc/modprobe.d/dell_wmi.conf
install dell_wmi /bin/true

Vendor modules are always trouble.

Hardware: https://ubuntu.com/certified/202111-29708/20.04%20LTS
Renoir graphics with Ryzen 5 5625U.

Symptoms:

• /sys/class/backlight/acpi_video0/brightness exists and contains values and can be changed but will not change the actual brightness on the laptop panel.

• Whenever a value is written to the above file, the Display Settings pop up. Yes, the actual xfce4-display-settings program is started. I'm assuming that it detects a display change. It even pops up if you use the Fn buttons to change the brightness if you have given control of the brightness to xfce4-power-manager (which you should).

• The Fn keys will emit "dell_wmi: Invalid length of WMI event" but this is a red herring, ignore this sort of warning.

• Your laptop's panel will only go up to 70Hz or 77Hz.

I tried many of the solutions that float around the web and only a combination of two of them plus something that I found myself in synaptic worked. Specifically:

(As root)

• Enable backports and install the kernel 5.18.0-0.bpo.1-amd64 (headers and image)

• Edit /etc/default/grub and change the CMDLINE to: GRUB_CMDLINE_LINUX_DEFAULT="quiet amdgpu.backlight=0"

• Run update-grub.

• Install firmware-amd-graphics

Reboot and acpi_video0 will go away and instead you'll have amdgpu_bl0 which actually works with Fn keys and by writting values to the /sys/class/backlight/amdgpu_bl0/brightness file. You'll also have 120Hz refresh rate.

I had tried individually the three important components of the solution and they didn't seem to work.

The only other issue that I encountered with this laptop was that the external mic doesn't work with ALSA at all, and the internal mic works but has no volume control. Pulseaudio somehow makes them work, which makes me think that there is a way to make them work with ALSA too, since PA uses ALSA if I am not mistaken. I may try to solve that in the future since I dislike PAs overhead (CPU and latency).

I hope this helps someone.