On my laptop (TUXEDO Aura 15 laptop,
cat /proc/cpuinfo => AMD Ryzen 4500U with (integrated)
Radeon Graphics) with Qubes OS the backlight control does not work (backlight always uncomfortably bright). In short pressing the dedicated brightness key strokes
[fn+F8/F9] changes the value in
/sys/class/backlight/acpi_video0/brightness, but it does not affect the brightness of my screen (instead just opens the “[Dom0] Display” configuration window). (A more comprehensive analysis of the symptoms has been discussed here: Changing brighness via shortcut fails to change screen brighness)
On a Ubuntu Live System running on my laptop the brightness control works, but in Ubuntu I find the directory
/sys/class/backlight/amdgpu_bl0 instead of
/sys/class/backlight/acpi_video0/brightness in Qubes OS. I guess the difference is that Ubuntu has the appropriate GPU driver at hand. However, I am not an expert.
My questions are:
- What is the difference between
/sys/class/backlight/acpi_video0/brightness? Is it that Ubuntu uses the appropriate GPU driver?
- If yes, does that mean that the appropriate GPU driver is a prerequisite that brightness control can work on my laptop?
- If yes or no, does this indicate a way to fix or enable brightness control on my laptop by another way than through the GPU driver? (I would prefer that for security reasons.)