Lost screen backlight controls after upgrade to F37

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1

I have a System76 Lemur Pro. Since upgrading to F37 I’ve lost the ability to control the screen brightness in Gnome and via the function keys. The folder /sys/class/backlight doesn’t exist and from what I’ve been reading it should be there.

CometLake graphics

$ lspci -k | grep -EA3 'VGA|3D|Display'
00:02.0 VGA compatible controller: Intel Corporation CometLake-U GT2 [UHD Graphics] (rev 02)
	DeviceName: VGA compatible controller
	Subsystem: CLEVO/KAPOK Computer Device 1401
	Kernel driver in use: i915
	Kernel modules: i915

Kernel includes "acpi_backlight=intel

$ cat /proc/cmdline 
BOOT_IMAGE=(hd0,gpt2)/vmlinuz-6.1.5-200.fc37.x86_64 root=UUID=28730e9c-57a9-4dd4-9aa7-f4eb451cae1f ro resume=/dev/mapper/fedora_localhost--live-swap rd.lvm.lv=fedora_localhost-live/root rd.luks.uuid=luks-7a875e5b-a21e-4e99-9cf6-399a7bd21e5a rd.lvm.lv=fedora_localhost-live/swap rhgb quiet splash acpi_backlight=intel


$ lsmod | grep i915
i915                 3436544  53
drm_buddy              20480  1 i915
drm_display_helper    208896  1 i915
cec                    81920  2 drm_display_helper,i915
video                  65536  1 i915
ttm                    94208  1 i915

Attempting to use the function keys to adjust the brightness yields the following in the syslog:

Failed to set new screen percentage: GDBus.Error:org.gtk.GDBus.UnmappedGError.Quark._gsd_5fpower_5fmanager_5ferror.Code1: No usable backlight could be found!

What other info can I provide to help fix this?

2

On the next boot try removing this splash acpi_backlight=intel from the kernel command line and see what the result is. I do not have and have never had that in my kernel command line and I see this on my laptop. My laptop has intel + nvidia GPUs.

$ ls /sys/class/backlight/intel_backlight/
actual_brightness  bl_power  brightness  device  max_brightness  power  scale  subsystem  type  uevent
3

Removing those entries didn’t work.

4

Aha! I set it to “acpi_backlight=native” and it worked! In case someone else finds this thread…

edit /etc/default/grub and include “acpi_backlight=native” at the end of your GRUB_CMDLINE_LINUX_DEFAULT stanza:

GRUB_CMDLINE_LINUX_DEFAULT="acpi_backlight=native"

Save your config and run “sudo grub2-mkconfig”. Reboot.

ref: Backlight - ArchWiki

ironically, I often find the best documentation for Fedora in the Archlinux wiki.

3 Likes
5

Sorry to pile on what looks like the solution to this question, but one clarifying question that I was having trouble getting a clear answer on through Google - is sudo grub2-mkconfig the full command there, or is there a path that you had to type afterward, like sudo grub2-mkconfig --output=<filename here>?

Thanks!

6

I’m no grub expert, but all I typed was what is in the quotes.

7

The actual command must have an output file for it to write to a file. Without specifying an output file it writes the output to the screen.

The command is sudo grub2-mkconfig -o /boot/grub2/grub.cfg

To find out what a command does use the man page, as man grub2-mkconfig
You also can peruse the many threads that contain that command, or see the official documentation at

8

Thanks for the file location info!

FWIW, that page on the Fedora Docs site has a banner at the top that it is deprecated, and “large parts of it are no longer current”, so I was a bit hesitant to assume.

I appreciate the help!

1 Like
9

That doc page was updated fairly recently and I believe is current for all releases since fedora 34.