Comment 4 for bug 1944094

Update to my previous comment - I've extensively tested different configurations (mostly kernel parameters) on my Legion 5 15ach6. I did manage to get the brightness to change when using just the dedicated GPU (selected as such within the BIOS,) using the parameter --

nvidia.NVreg_RegistryDwords=EnableBrightnessControl=1

This causes the nvidia gpu to show up in /sys/class/backlight/ and writing to the control files works as intended. However, in hybrid mode the dGPU is alongside the iGPU, but modifying either of the /sys/class/backlight/*/brightness files does nothing.

In integrated only mode (using optimus-manager to disable the dGPU, I think its still technically still hybrid mode, but xorg doesn't know the dGPU exists.)

acpi_backlight=video/vendor/native/none

all do nothing, i tested each individually with

amdgpu.backlight=1 and amdgpu.backlight=0,

and did not get any hint of a way to control backlight, only the AMD iGPU showed up in /sys/class/backlight/, (because it was integrated only) and changing the brightness value did nothing.

Something else of note was that I noticed that when using just the dedicated NVIDIA card, xrandr showed DP-1 as the active montior, while when I was using the AMD iGPU, it was showing as eDP. Does anyone know if the MUX switch needs something from the kernel or nvidia driver to work properly? Is there any way for us to be able to check the position of the switch?