Brightness controls being applied to incorrect graphics driver when cinnamon is active desktop environment

Distribution

Mint 21.1

Package version

5.6.8

Graphics hardware in use

Intel Corporation TigerLake-H GT1 [UHD Graphics] & NVIDIA Corporation GA107BM [GeForce RTX 3050 Mobile]

Frequency

Always

Bug description

Self-diagnosis has been chronicled here: (https://forums.linuxmint.com/viewtopic.php?p=2327170)

The full fledged description can be seen at the link above, I'll try to truncate it here. Essentially, the brightness controls on my laptop direct changes to the wrong graphics driver. When my laptop is set to "discrete" and only using the nvidia graphics, then it works. If it's set to hybrid, then the display is drawn using the intel graphics, and as such the backlight is controlled by the "intel_backlight" files, rather than the "nvidia_0," both of which appear in /sys/class/backlight. When nvidia prime is set to "performance" or "on-demand," backlight changes do not work, as the values are still sent to the "nvidia_0" files. When set to "power saving mode," then the nvidia driver is inactive and not present in the /sys/class/backlight.

Steps to reproduce

Essentially, values need to be sent to the active driver, in my case being "intel_backlight" and when the files in there are changed manually, the hardware responds (I'm limping by with a script I found that is getting the job done). Again, specifics are outlined in the link above, but I isolated this down to cinnamon by booting into pop_os live, seeing brightness works with intel active, installed that distro, installed Cinnamon on that distro, booted into cinnamon, and lost brightness control. I then went back to Mint, installed MATE, logged into MATE, brightness works as expected. Logged out of mate, back into cinnamon, brightness control lost.

Expected behavior

Brightness controls would change the values of whatever graphics driver is being used to draw the display, or potentially change both drivers values if need be

Additional information

I'll link to my mint forums thread again here: (https://forums.linuxmint.com/viewtopic.php?p=2327170)

and in that forum thread I linked to a KDE bug tracker that somebody reported the same issue and appears to be corrected: (https://invent.kde.org/plasma/powerdevil/-/commit/761fc8a4bf4bd70bcd9aca63fc67382c94ecf884)

Start by reviewing the linked Linux Mint forum thread and the KDE PowerDevil commit for the corresponding hybrid-graphics brightness behavior. Trace Cinnamon's brightness-control handling for systems exposing intel_backlight and nvidia_0, then verify that controls target the active display driver in hybrid and power-saving modes.