Bug 510264

Summary:	Screen goes black when decreasing screen brightness from 50% to 45% using Fn keys
Product:	[Plasma] plasmashell	Reporter:	Niko Lockenvitz <kde>
Component:	Power management & brightness	Assignee:	Plasma Bugs List <plasma-bugs-null>
Status:	RESOLVED UPSTREAM
Severity:	normal	CC:	nate
Priority:	NOR
Version First Reported In:	6.4.5
Target Milestone:	1.0
Platform:	Arch Linux
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:

Description Niko Lockenvitz 2025-10-05 13:55:42 UTC

SUMMARY
Screen goes black / 0% brightness whenever I decrease screen brightness using Fn keys and I pass the 50% mark (50% -> 45%).

STEPS TO REPRODUCE
1. Use Fn keys to increase brightness to 50%.
2. Press Fn key to decrease brightness (5% step).
3. Screen goes completely black / off. (Should be 45%)
4. Press decrease again, stays black. (Should be 40%)
5. Press Fn key to increase brightness. Screen is lit again. Shows 40% brightness. (Should be 45%).

OBSERVED RESULT
Screen goes black.

EXPECTED RESULT
Screen doesn't go black and there shouldn't be a 5% deviation in the end.

SOFTWARE/OS VERSIONS
Operating System: Arch Linux 
KDE Plasma Version: 6.4.5
KDE Frameworks Version: 6.18.0
Qt Version: 6.9.2
Kernel Version: 6.16.10-arch1-1 (64-bit)
Graphics Platform: Wayland
Graphics Processor: AMD Radeon Graphics

ADDITIONAL INFORMATION

Comment 1 Nate Graham 2025-10-07 18:56:43 UTC

Can you run `cat /sys/class/backlight/*/brightness` and paste the output here, first when the brightness is at 50%, and then again when you reduce it to 45% to trigger the bug?

Comment 2 Niko Lockenvitz 2025-10-09 17:28:56 UTC

# increase brightness to 50 % with Fn+F6
$ cat /sys/class/backlight/*/brightness
32768

# decrease brightness with Fn+F5 (screen goes completely black)
$ cat /sys/class/backlight/*/brightness
29491

# increase brightness with Fn+F6 (now at 45% and screen is lit)
$ cat /sys/class/backlight/*/brightness
29491

Comment 3 Nate Graham 2025-10-10 15:52:44 UTC

Thanks. This seems like a GPU driver bug, or possibly even a hardware issue; a brightness value of 29491 should not be turning off the backlight entirely! That's whacko. I'd recommend reporting the issue upstream; see https://docs.mesa3d.org/bugs.html for how to do that.