KDE Neon Brightness Control vanished

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21

I get the following output:

total 0
-r–r–r-- 1 root root 4096 Okt 28 13:56 connector_id
lrwxrwxrwx 1 root root 0 Okt 28 15:18 ddc → i2c-12
lrwxrwxrwx 1 root root 0 Okt 28 13:51 device → …/…/card1
-r–r–r-- 1 root root 4096 Okt 28 15:48 dpms
drwxr-xr-x 3 root root 0 Okt 28 13:50 drm_dp_aux0
-r–r–r-- 1 root root 0 Okt 28 13:56 edid
-r–r–r-- 1 root root 4096 Okt 28 13:56 enabled
lrwxrwxrwx 1 root root 0 Okt 28 15:48 firmware_node → …/…/…/…/…/LNXSYSTM:00/LNXSYBUS:00/PNP0A08:00/LNXVIDEO:00/device:16
drwxr-xr-x 4 root root 0 Okt 28 13:50 i2c-12
-r–r–r-- 1 root root 4096 Okt 28 15:48 modes
drwxr-xr-x 2 root root 0 Okt 28 15:48 physical_location
drwxr-xr-x 2 root root 0 Okt 28 15:48 power
-rw-r–r-- 1 root root 4096 Okt 28 13:50 status
lrwxrwxrwx 1 root root 0 Okt 28 13:50 subsystem → …/…/…/…/…/…/class/drm
-rw-r–r-- 1 root root 4096 Okt 28 13:50 uevent
-r–r–r-- 1 root root 4096 Okt 28 15:48 waiting_for_supplier

22

So, the problem is that the intel_backlight device isn’t available on the eDP connection. This could be caused by various issues with the system configuration - Ubuntu has this useful article for debugging backlight issues, which I think you should review and try some of the suggestions there. The article is mostly focused about providing details to the Ubuntu support team, but you can just try some of their suggestions and see if you can get intel_backlight to appear.

I recommend trying first either the acpi_backlight=vendor kernel parameter or the video.use_native_backlight=1 kernel parameter.

The document links to an explanation on how to change kernel parameters, but I find it more useful to do the following:

  1. Launch Kate and use it to open /etc/default/grub
  2. Add your kernel parameter to the GRUB_CMDLINE_LINUX_DEFAULT variable (inside the double quotes
  3. Save - you should be prompted for your password to allow writing to the system configuration folder.
  4. Run, from the main menu, krunner, Kate terminal or wherever:
    systemd-run update-grub - you should be prompted for your password to allow updating the boot configuration.
  5. Reboot.

Lather-rinse-repeat until you get the correct kernel parameter for your system.

23

I finally managed to fix the problem!

My standard configuration was GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=vendor acpi_osi=linux"

I changed it to GRUB_CMDLINE_LINUX_DEFAULT="quiet splash pcie_aspm=force acpi_backlight=native". After a reboot, everything worked normally again.

Thank you very much for your help!

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