Bug 494183

Summary:	Regular black screen on second monitor when using DisplayPort cable
Product:	[Plasma] kwin	Reporter:	Matt <mattrydr>
Component:	platform-drm	Assignee:	KWin default assignee <kwin-bugs-null>
Status:	RESOLVED NOT A BUG
Severity:	normal	CC:	kdedev, kotarf
Priority:	NOR	Keywords:	wayland-only
Version First Reported In:	6.1.5
Target Milestone:	---
Platform:	Arch Linux
OS:	Linux
Latest Commit:		Version Fixed In:
Sentry Crash Report:

Description Matt 2024-10-05 21:35:48 UTC

SUMMARY

I've found an issue where my second monitor goes black for approx. 750-1500ms while I'm hooked up to my laptop with a USB-C to DisplayPort cable. The screen then returns after the timeout, only for it to happen again in ~10 minutes.
Looking through journalctl, this line is always correlated with the blackout.

`Oct 05 22:19:58 m-laptop kwin_wayland[870]: kwin_scene_opengl: 0x2: GL_INVALID_OPERATION in glDrawBuffers(unsupported buffer GL_BACK_LEFT)`

There's sometimes some extra parts output, this one about plugin not supporting raise():

`Oct 05 22:28:22 m-laptop kwin_wayland[870]: This plugin does not support raise()
Oct 05 22:28:22 m-laptop kwin_wayland[870]: kwin_scene_opengl: 0x2: GL_INVALID_OPERATION in glDrawBuffers(unsupported buffer GL_BACK_LEFT)
`
I don't have the info for it, but there's also a log about something about the aspect ratio not being what was expected - I'll update the report if I see that again.

STEPS TO REPRODUCE
1. Connect a laptop to a screen with a USB-C to DisplayPort cable
2. Use the computer for ~10-15 minutes

OBSERVED RESULT
You should get the blackout for a second, it's fairly regular.

EXPECTED RESULT
Probably that it doesn't do that.

SOFTWARE/OS VERSIONS
➜ ~ kinfo
Operating System: Arch Linux
KDE Plasma Version: 6.1.5
KDE Frameworks Version: 6.6.0
Qt Version: 6.7.2
Kernel Version: 6.10.10-arch1-1 (64-bit)
Graphics Platform: Wayland
Processors: 8 × Intel® Core™ i7-8650U CPU @ 1.90GHz
Memory: 15.5 GiB of RAM
Graphics Processor: Mesa Intel® UHD Graphics 620

ADDITIONAL INFORMATION
I've tried fiddling with the display options, setting scale from 125% to 100%, changing the refresh rate from 120, 100, 60Hz.
I have also just found a HDMI cable, so I'll find out if that's doing it also.
If any further info would be helpful, let me know.

Comment 1 TraceyC 2024-10-07 15:27:25 UTC

I have definitely seen this effect on 6.1.5 with a laptop connected to a DisplayPort monitor

Laptop -> USB C cable -> Dock -> DP cable -> Monitor

I have these entries in journalctl today even though I have not seen the blackout today, so they may or may not be related

t 07 09:30:20 tlc-xps17-solus kwin_wayland[1506]: kwin_scene_opengl: 0x3: GL_INVALID_OPERATION in glDrawBuffers(unsupported buffer GL_BACK_LEFT)
Oct 07 09:30:20 tlc-xps17-solus kwin_wayland[1506]: kwin_scene_opengl: 0x3: GL_INVALID_OPERATION in glDrawBuffers(unsupported buffer GL_BACK_LEFT)
Oct 07 09:30:20 tlc-xps17-solus kwin_wayland[1506]: kwin_scene_opengl: 0x3: GL_INVALID_OPERATION in glDrawBuffers(unsupported buffer GL_BACK_LEFT)
Oct 07 09:30:32 tlc-xps17-solus kwin_wayland[1506]: This plugin does not support raise()


Oct 07 09:35:59 tlc-xps17-solus kwin_wayland[1506]: kwin_scene_opengl: 0x3: GL_INVALID_OPERATION in glDrawBuffers(unsupported buffer GL_BACK_LEFT)
Oct 07 09:41:54 tlc-xps17-solus kwin_wayland_wrapper[1590]: Key repeat discarded, Wayland compositor doesn't seem to be processing events fast enough!

I'm in the process of setting up git-master on this system, when that's done I'll re-test with master, if someone else doesn't get to that first.

Comment 2 Matt 2024-10-08 16:43:29 UTC

I've downgraded to 6.1.0, and everything actually looks like it's working, albeit it's only been around 30m since I've done so.
However, no black screens so far.

I'll try bumping up patch versions until I get to the one that must've introduced the issue, and report back with the details. It might be in a few days as I want to make sure I'm not just getting lucky between revisions.

And on the HDMI note, that's fine, as you might expect. However, I can't go back to 30Hz..!

Comment 3 Matt 2024-10-10 18:06:43 UTC

No, sorry, got everyone's hopes up. Still getting a blackout occasionally with that version.
Being on Arch, I tried installing `kwin` 6.0.5, but that doesn't get me into a session at all.

Comment 4 Matt 2024-11-03 15:12:53 UTC

This turned out to be a crap USB-C to Displayport cable.

Since reporting this issue, I managed to get a Windows PC, and that exhibited the same issue. The event viewer reported an issue with `nhi`, yet I'm unsure if that's correlated there.

I bought another one from Startech (other brands also available) and that ones been more reliable. I haven't seen the issue since.