Bug 505107

Summary:	Background flickers through to foreground when using Display Stream Compression via DisplayPort
Product:	[Plasma] kwin	Reporter:	Mike Dawson <mikedawson>
Component:	general	Assignee:	KWin default assignee <kwin-bugs-null>
Status:	RESOLVED UPSTREAM
Severity:	normal	CC:	mikedawson, xaver.hugl
Priority:	NOR
Version First Reported In:	unspecified
Target Milestone:	---
Platform:	Other
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:

Description Mike Dawson 2025-06-01 23:23:31 UTC

SUMMARY
When using an nvidia RTX 3090 or RTX 4090 and DSC over Displayport, the background will randomly flicker through to the foreground.  This is especially annoying in fullscreen Youtube videos.

I've noticed this bug for several years, so it was happening on KDE5 as well. This has happened on every nvidia driver from 535 through 575.  At first I thought it was just an nvidia driver bug, but this does not happen in Gnome.

STEPS TO REPRODUCE
1. Use Display Stream Compression (high resolution and refresh rate) over Displayport
2. Use NVidia card
3. Use Wayland
4. fullscreen a Youtube video and wait a minute (note it also happens to normal windows during regular work, not watching videos)

OBSERVED RESULT
Background flickers through to the foreground

EXPECTED RESULT
no flickering

SOFTWARE/OS VERSIONS

CachyOS Kernel 6.15
KDE Plasma Version: 6.3.5
KDE Frameworks Version: 6.14
Qt Version: 6.9

ADDITIONAL INFORMATION
This has happened for years, so these versions listed here are not the cause

Switching to a lower refresh rate, or switching to Gnome solves the issue

Comment 1 Zamundaaa 2025-06-02 14:01:28 UTC

KWin has neither control nor even knowledge about DSC. Please report this to NVidia at https://forums.developer.nvidia.com/c/gpu-graphics/linux.

Comment 2 Mike Dawson 2025-06-02 17:33:46 UTC

(In reply to Zamundaaa from comment #1)
> KWin has neither control nor even knowledge about DSC. Please report this to
> NVidia at https://forums.developer.nvidia.com/c/gpu-graphics/linux.

since this doesn't happen in Gnome, I assumed it was a KDE bug

Comment 3 Zamundaaa 2025-06-02 18:15:26 UTC

There are a large random-seeming reasons for why synchronization bugs can become visible or invisible, and it not happening on Gnome for you doesn't mean all that much. The difference could come from lower latency, higher bit depth, different compositing shaders, different optimizations, or anything else that can cause even tiny timing differences.

If the driver side investigation finds that we should be doing something differently, do reopen this bug report. But that driver side investigation needs to happen first - especially while other reports of artifacts with DSC are currently floating around, like https://forums.developer.nvidia.com/t/displayport-dsc-4k-240hz-flickering-artifacts/294490

Comment 4 Mike Dawson 2025-06-02 18:23:50 UTC

Thank you, I will post on the nvidia forums that you linked