Hello, I'm running Ubuntu Mate 22.04.1 LTS on my Lenovo Thinkpad x280 and I'm having issues with brightness control. If I use FN keys to set brightness, once rebooted the brightness is reset to what is in Power Management Preferences.
If I use xrandr or /sys/class/backlight/intel_backlight/brightness still the same, the brightness is reset to whatever is set in Power Management Preferences.
Basically, it doesn't matter what I do, the brightness settings are reset to whatever is set in Power Management Preferences -> Set display brightness to
I did changes to grub and whatever else, nothing changes. Please note that this wasn't happening on openSUSE with Xfce.
Welcome
I think it is operating normally.
Open the Power Management Preference screen.
On my UM22.04.1 Dell when I use fn keys to change screen brightness the slider (Set display brightness to:) in the PMP screen changes to current brightness level, thus when rebooting it would use that setting.
I might be missing something on my end though.
Yes, you are missing something. If I use the FN keys to set the brightness, it should stay like that after reboot, but it will always default to the Power Management settings. This would not happen on Xfce (openSUSE). I actually have the same issue even with the keyboard backlight, it was always on, no matter what until I found a 'workaround' online. Like I said before, the settings from FN or whatever should match everywhere else and should be saved once you reboot, should default to something else.
I do that and I get this.
fn key 65 reboot, check PM 65
fn key 100 reboot, check PM 100
fn key 5 reboot, check PM 5
Works here gif shows PM as using fn key
Until this is fixed in Ubuntu MATE, as a work around, you could create a script that sets the brightness at the desired level, then run that script at boot time using Startup Applications.
I'm not sure if this is really a kernel bug as one of the apps can control properly the blacklight, but not others, maybe the method is the issue, but not sure at all.
and compare it to my Thinkpad specs.
If kernel version, distro version and desktop version are the same as my Thinkpad, you can bet your bottom that the problem is in the UEFI/Motherboard-firmware (or whatever the BIOS is called these days).
That means that the behavioural difference it is highly likely due to a different ACPI implementation in UEFI/firmware which is motherboard bound. Nothing we can do about that.
Good. We even run the same video driver ( i915 ).
The only thing left to do is follow the advice of @goinglinux and report this as a bug.
The kernelteam can't fix the BIOS for you but they can (and did so numerous times) patch the umpteenth ACPI workaround in the kernel.
You might have a very small chance to fix it yourself by doing a BIOS update but I wonder if it's worth the hassle and the risk.
On my work laptop (the Acer) i have the same behaviour. I never thought about it actually.
Maybe because I couldn't care less. I'm used to it and it has some pro's actually.
If you feel like experimenting a bit,
there are several thinkpad tools:
apt search thinkpad
and several backlight tools
apt search backlight
If you have the GUI-packet manager "synaptic" installed, it makes it a bit easier to browse around in the repository, like , it gives you the packetnames and descriptions in one go.
