https://bugs.kde.org/show_bug.cgi?id=513812
Bug ID: 513812
Summary: Desktop locks up whenever a 4th output is enabled from
my GPU. Only happens on Wayland.
Classification: Plasma
Product: kwin
Version First 6.5.3
Reported In:
Platform: Fedora RPMs
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: platform-drm
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Target Milestone: ---
Created attachment 187978
--> https://bugs.kde.org/attachment.cgi?id=187978&action=edit
Combined logs from dmesg at boot, dmesg during the error and journalctl
SUMMARY
Whenever I try to enable a 4th monitor from my GPU, it either hangs (through
kscreen-doctor) until i blindly type the command to disable it again. When done
through system settings, it just says "Driver rejected the output
configuration".
It does not matter which monitor or on which output it is. I've tried every
combination I could think of and 3 monitors always works fine, but the second I
enable the 4th, the entire desktop graphically freezes (it's still running
under that, I can up arrow, ctrl backspace to replace the .enable with .disable
to get it fixed) or it just refuses to apply. It doesn't matter whether the 4th
monitor is DP or HDMI, it's just when it gets to four.
I've tried it on Arch Linux, Kubuntu 25.10 and Fedora 43. Sadly I don't know
the exact version of kwin where this broke, as I reinstalled instead of
updating and didn't take note of what package versions I had installed
previously... But I'm very sure I was already on Plasma 6.5. My educated guess
is 6.5.3 but take that with a margin of error of 6.5.2 through 6.5.4..
Apologies for that. I've tried reverting to previous versions with little luck
bcs of dependency errors, couldn't find every single RPM it wanted for
dependencies. I've also tried this in a development environment with every KDE
package compiled myself, but there were many more issues that got in the way
first, so I couldn't capture the logs on there, but it did seem to exhibit the
same general behavior.
Only happens on Wayland. Xorg session works fine with all 4 (and the 2 on mobo,
for a total of 6) monitors. But I have an HDR monitor and require many more
Wayland features...
I've also tried the legacy modesetting (KWIN_DRM_NO_AMS) in kwin and the same
behaviour occurs, although it just says modesetting failed and not atomic
modeset..
This started happening around the start of this month, but I've just disabled
my 4th GPU monitor for now.
STEPS TO REPRODUCE
1. Enable a 4th monitor from the GPU, either through system settings or
kscreen-doctor
My logs were obtained through the following sequence of commands:
```
echo "BEGIN LOGS" | sudo tee /dev/kmsg && echo 0x1FF | sudo tee
/sys/module/drm/parameters/debug && kscreen-doctor output.HDMI-A-1.enable &&
sleep 1 && kscreen-doctor output.HDMI-A-1.disable && sleep 0.5 && echo 0 | sudo
tee /sys/module/drm/parameters/debug && echo "END LOGS" | sudo tee /dev/kmsg
```
My session was also started with the following in .config/plasma-workspace/env:
(taken from
https://invent.kde.org/plasma/kwin/-/wikis/Debugging/Debugging-DRM-issues)
export QT_LOGGING_RULES="kwin_*.debug=true"
export LC_ALL=C
With the logs then being obtained through `journalctl -xe --user -f | grep
--ignore-case --extended-regexp "kwin|kde|plasma"` and `sudo dmesg -w`. Since I
don't see how to add multiple attachments I concatenated these logs (alongside
the dmesg at boot) with:
```
echo "=== boot-dmesg.log: ===" > all.log; cat boot-dmesg.log >> all.log; echo
"=== after-kscreen-journalctl.log: ===" >> all.log; cat
after-kscreen-journalct.log >> all.log; echo "=== after-kscreen-dmesg.log: ==="
>> all.log; cat after-kscreen-absurdly-long.log >> all.log
```
OBSERVED RESULT
"applying config failed! The driver rejected the output configuration", along
with a lot of "Atomic modeset test failed! Invalid argument" in journalctl
(without debug on this is all it shows)
EXPECTED RESULT
I can enable a 4th monitor.
SOFTWARE/OS VERSIONS
Linux/KDE Plasma: 6.17.12-300.fc43-.x86_64
KDE Plasma Version: 6.5.4-2
KDE Frameworks Version: 6.21.0
Qt Version: 6.10.1
ADDITIONAL INFORMATION
I've tested this on an Intel Arc B580 and an AMD Radeon 7900 XT, both show the
exact same behaviour.
I have two monitors plugged into my motherboards running on integrated
graphics, but even without these the same happens.
Also, importantly, this doesn't happen in other desktop environments, just KDE
Plasma and just in Wayland. It also did seem to work in the Kubuntu 25.10 live
image from what I recall, but not after installation (which would have newer
package versions)
Thanks in advance! Please let me know if there's anything I can do to help
provide more information or troubleshoot!
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