Backlight control keys not working anymore on latest Kernel

General system Kernel, boot, graphics & hardware
1

I have a Lenovo ThinkPad L14 Gen 5, here’s my situation

  • 6.12.45-1-lts: Everything works fine
  • 6.16.5-arch1-1:
    • Backlight keys don’t work, nothing on xev or evtest
    • brightnessctl do work, but xbacklight don’t
    • brightness module on polybar can only decrease backlight

What I tried:

  • $ ls /sys/class/backlight/ -> amdgpu_bl1
  • acpi_backlight=vendor -> don't work
  • acpi_backlight=video + amdgpu.backlight=0 -> don't work

For the time being I just stay on LTS kernel, but I guess this will become a problem sooner or later, so any suggestions are welcome

2

On my T14 Gen 1 I have intel_backlight (no AMD GPU). That continues to work nicely, as well as the keyboard backlight.

Kernel also 6.16.5-arch1-1 here.

3

Guess the issue is AMD specific then damn

4

Hi, this looks like a regression in the amdgpu backlight driver introduced around kernel 6.16.5. Since it works on the LTS kernel, you should report it upstream so the maintainers can fix it, maybe here https://gitlab.freedesktop.org/drm/amd/-/issues and/or here https://bugzilla.kernel.org/

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5

Will do, thanks for the link

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6

Sharing my discovery, this was actually a problem due to a recent change in amdgpu and my config.

In LTS, max_brightness is set to 255, but in latest kernel it is set the 64764.

Now the thing is that my i3 config was set to bind an increase/decrease of 10 units on XF86MonBrightnessUp/XF86MonBrightnessDown events, giving the impression it was not working, while it was actually working, but just taking forever.

My solution was to use percentage instead:
bindsym XF86MonBrightnessUp exec brightnessctl set 5%+

It does not fix my polybar issue, but it’s probably another problem anyway

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