Bug 460517

Summary: Plasma 5.26 completely breaks my multi-monitor setup
Product: [Plasma] kwin Reporter: Stefan Radermacher <kde>
Component: multi-screenAssignee: KWin default assignee <kwin-bugs-null>
Status: RESOLVED DUPLICATE    
Severity: normal CC: hajit.00, mrmazda, nicolas.fella
Priority: NOR    
Version: 5.26.0   
Target Milestone: ---   
Platform: Gentoo Packages   
OS: Linux   
Latest Commit: Version Fixed In:
Sentry Crash Report:

Description Stefan Radermacher 2022-10-16 07:50:39 UTC
SUMMARY
***
After updating to Plasma 5.26 my system now becomes completely unusable after waking up from power save mode, or after switching the monitors that I use for multiple machines back to the KDE machine.

Let me describe my screen setup.
1) My main screen is a 4K monitor at 3840×2160 resolution, connected to the DP-0 port.
2) My secondary screen is an HD monitor at 1920×1080 resolution, connected to HDMI-0.
3) My main screen is to the right of the secondary screen.

Until Plasma 5.26 this has mostly worked, but with flaws: when the system wakes up or regains control of the monitors, windows on the main screen were moved around a certain distance to the left, overlapping both monitors. Some windows on the main screen that were maximized vertically were resized to the lesser height of the secondary screen. Rather annoying, but more or less workable.

Now, with Plasma 5.26 this behavior has been replaced with something even worse. When the system wakes up now, the main monitor is completely deactivated (“NO SIGNAL”), and plasma tries to paint both screens on the secondary monitor. The screens overlap on the secondary monitor, and the screen that is too big scrolls around in the top half of the monitor when I move the mouse pointer. The system is completely unusable after that.

By the way, after killing the X-Server and logging in again, the main monitor keeps being deactivated until I manually delete the folder ~/.local/share/kscreen.
***


SOFTWARE/OS VERSIONS
Linux/KDE Plasma:  Plasma
KDE Plasma Version: 5.26
KDE Frameworks Version: 5.99 
Qt Version: 5.15.5
Comment 1 Stefan Radermacher 2022-10-16 07:53:12 UTC
Additional info: I've tried this with a separate, new user account, the effects are the same.
Comment 2 Viktor 2022-10-18 17:07:42 UTC
Similar situation here. Primary 2K monitor via DP, and FHD monitor via HDMI. After updating to Plasma 5.26 2K monitor is disabled. Enabling it in Display Configuration does nothing. I can enable it only in NVidia-Settings. and it works until I power off monitor, after power on it again disabled.
Comment 3 Felix Miata 2022-10-22 05:41:32 UTC

*** This bug has been marked as a duplicate of bug 450068 ***
Comment 4 Stefan Radermacher 2022-10-22 07:57:44 UTC
I'm not sure that this is really a duplicate of bug 450068. That bug already occurs in Plasma 5.24, but my problem is new with 5.26, previously this catastrophic failure did not occur.
Comment 5 Felix Miata 2022-10-22 10:16:27 UTC
It really doesn't matter whether this is dup'd to bug 450068 or bug 385135 or some other "multi-screen support" bug. The fix for 450068 when it arrives will be fixing multiple bugs that were made worse, or were unhelped by, or were new in, 5.26. In the mean time, disable automatic KScreen2 startup and manage displays with xrandr/arandr as best suits your own setup, if X automagic display management doesn't work well enough on its own without KScreen2 interference.
Comment 6 Stefan Radermacher 2022-10-22 10:47:47 UTC
(In reply to Felix Miata from comment #5)
> It really doesn't matter whether this is dup'd to bug 450068 or bug 385135
> or some other "multi-screen support" bug. The fix for 450068 when it arrives
> will be fixing multiple bugs that were made worse, or were unhelped by, or
> were new in, 5.26. In the mean time, disable automatic KScreen2 startup and
> manage displays with xrandr/arandr as best suits your own setup, if X
> automagic display management doesn't work well enough on its own without
> KScreen2 interference.

How would I best “disable automatic KScreen2 startup”?
Comment 7 Stefan Radermacher 2022-10-22 10:55:28 UTC
> (In reply to Felix Miata from comment #5)
> How would I best “disable automatic KScreen2 startup”?

Never mind, I found it.