Bug 487900

Summary:	Unreliable external screen brightness control
Product:	[Unmaintained] Powerdevil	Reporter:	Iyán M. V. <me>
Component:	general	Assignee:	Plasma Bugs List <plasma-bugs-null>
Status:	RESOLVED FIXED
Severity:	normal	CC:	jpetso, me, natalie_clarius, nate
Priority:	NOR
Version First Reported In:	git-stable-Plasma/6.1
Target Milestone:	---
Platform:	Other
OS:	Linux
Latest Commit:		Version Fixed In:	6.1.2
Sentry Crash Report:
Attachments:	Invalid brightness 1 Invalid brightness 2 Slides in Power Management

Description Iyán M. V. 2024-06-01 22:04:29 UTC

SUMMARY

I think I was never able to control my external monitor (Dell U2518D) brightness from Plasma, so I was surprised to see it in the "Brightness and Color" applet after updating to Plasma 6.1 Beta. Super cool feature! It is way faster than using the screen built-in menu.

Unfortunately, even though it works perfectly after booting, it becomes a bit unreliable over time. It has happened already a few times but I still couldn't manage to find an exact series of steps to reproduce the issue.

At some point, the slider doesn't do anything any more. Other times, the brightness is changed to the very minimum, and after that trying to move the slides shows weird values like "inf%" or "nan%".

I'm happy to help debug this since probably it's a very hardware specific thing, but perhaps someone else can replicate the issue with other monitors?


STEPS TO REPRODUCE
1. Start Plasma
2. Lock the screen a few times
3. Turn off and on the monitor a few times
4. Wait and repeat previous steps

OBSERVED RESULT
Brightness control at some point stops working

EXPECTED RESULT
Brightness control is reliable


SOFTWARE/OS VERSIONS
Operating System: Arch Linux 
KDE Plasma Version: 6.0.90
KDE Frameworks Version: 6.2.0
Qt Version: 6.7.1
Kernel Version: 6.9.3-arch1-1 (64-bit)
Graphics Platform: Wayland
Processors: 24 × AMD Ryzen 9 7900X3D 12-Core Processor
Memory: 93.5 GiB of RAM
Graphics Processor: AMD Radeon RX 7900 XT
Manufacturer: ASUS

Comment 1 Iyán M. V. 2024-06-01 22:08:54 UTC

Created attachment 170052 [details]
Invalid brightness 1

Comment 2 Iyán M. V. 2024-06-01 22:09:06 UTC

Created attachment 170053 [details]
Invalid brightness 2

Comment 3 Iyán M. V. 2024-06-01 22:46:52 UTC

Created attachment 170056 [details]
Slides in Power Management

I just realized that even though the slider in the Brightness and Color applet does not work, the one in System Settings -> System -> Power Management still works.

Comment 4 Jakob Petsovits 2024-06-03 02:22:14 UTC

Hm, I wonder if turning off the only monitor results in an invalid max brightness value being sent from PowerDevil to the applet that it doesn't know how to handle properly. Worth investigating.

Comment 5 Iyán M. V. 2024-07-08 07:29:44 UTC

Probably related to Bug 489169 ?

Comment 6 Nate Graham 2024-07-10 20:57:40 UTC

Quite likely, and that's supposed to be fixed in 6.1.2. Are you still able to reproduce the issue in that release or later?

Comment 7 Iyán M. V. 2024-07-15 07:44:13 UTC

Yes, this seems to work just fine now, awesome! I still get some powerdevil crashes but I can't reproduce the bug as I described above, so closing this :)