Bug 494923

Summary:	Since 6.2.0, using DisplayPort 2.1 (SDR) results in a significantly darker image.
Product:	[Plasma] kwin	Reporter:	Naxdy <xnaxdy>
Component:	platform-drm	Assignee:	KWin default assignee <kwin-bugs-null>
Status:	RESOLVED NOT A BUG
Severity:	normal	CC:	bugreports61, jpetso, xaver.hugl
Priority:	NOR	Keywords:	regression
Version First Reported In:	6.2.0
Target Milestone:	---
Platform:	Other
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:
Attachments:	drm_info DisplayPort 1.4 drm_info DisplayPort 2.1 (FreeSync On) drm_info DisplayPort 2.1 (FreeSync Off)

Description Naxdy 2024-10-17 11:02:43 UTC

SUMMARY
Since 6.2.0, using DisplayPort 2.1 (DR) results in a significantly darker image. It is possible to work around this bug (on my particular monitor) by using HDR and cranking up the brightness, but this results in a different picture compared to before.

When I switch back my monitor to DisplayPort 1.4, the issue disappears, but this is not desirable since it doesn't support 240Hz under DisplayPort 1.4.

Also worth noting is that this only appears once KWin starts up. On a fresh boot, the SDDM login screen is displayed at the correct brightness level, but once the Plasma session starts, everything becomes significantly darker under SDR.

STEPS TO REPRODUCE
1. Enter a Plasma Wayland session using DisplayPort 2.1 and SDR

OBSERVED RESULT
The picture is very dark / washed out

EXPECTED RESULT
The picture looks the same compared to DisplayPort 1.4

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: NixOS
KDE Plasma Version: 6.2.0
KDE Frameworks Version: 6.7.0
Qt Version: 6.8.0

ADDITIONAL INFORMATION
-

Comment 1 Zamundaaa 2024-10-18 20:55:50 UTC

I have no idea what could be causing this; KWin doesn't know or care what the DisplayPort version is.
Maybe you could check if there's a difference in the output of drm_info? Or maybe the EDID is different?

Comment 2 Naxdy 2024-10-19 12:29:11 UTC

So, I just confirmed by booting into my previous config with 6.1.5 that this issue was definitely introduced (for me) in 6.2.

I've also found that enabling freesync fixes this issue as well (AMD GPU), though this is kind of redundant on Wayland.

There has been no Kernel update in the meantime. Mesa went from 24.2.2 -> 24.2.4.

I've pulled drm_info for the following configs:

- DisplayPort 1.4
- DisplayPort 2.1 + FreeSync On
- DisplayPort 2.1 + FreeSync Off

I'll attach them here momentarily.

Comment 3 Naxdy 2024-10-19 12:29:54 UTC

Created attachment 175019 [details]
drm_info DisplayPort 1.4

Comment 4 Naxdy 2024-10-19 12:30:10 UTC

Created attachment 175020 [details]
drm_info DisplayPort 2.1 (FreeSync On)

Comment 5 Naxdy 2024-10-19 12:30:28 UTC

Created attachment 175021 [details]
drm_info DisplayPort 2.1 (FreeSync Off)

Comment 6 bugreports61 2024-10-20 06:22:48 UTC

Hi,

i had the issue the brightness was cranked up automatically after login to kde , that also started with 6.2 . I suspect power devil as the source of those issues. I could get it fixed by following:  https://github.com/KDE/powerdevil/blob/master/README.md and disabling ddcutil for powerdevil. Maybe you could give it a try and see if it helps in your case ?

Br

Comment 7 Jakob Petsovits 2024-10-20 14:43:45 UTC

Possibly related to https://invent.kde.org/plasma/kwin/-/issues/238. But also perhaps not, I don't see why DP 2.1 would change anything about this.

(In reply to bugreports61 from comment #6)
> i had the issue the brightness was cranked up automatically after login to kde, that also started with 6.2.

That's Bug 494408, also with a fix in the works.

Comment 8 Naxdy 2024-10-20 19:27:02 UTC

So, turns out, as so often I like to say at work: "It's a feature, not a bug."

I didn't even know my external monitor's brightness could be controlled through software. Learn something new every day!

For some reason, after updating to 6.2 the brightness settings were either introduced for my particular device, or had changed to the point of reducing the brightness dramatically.

However, I can adjust the brightness to its intended setting via the "Brightness and Color" plasmoid.