Bug 508986

Summary: SDDM and kwayland issue
Product: [Frameworks and Libraries] kwayland Reporter: FingerlessGloves <kde>
Component: generalAssignee: Martin Flöser <mgraesslin>
Status: REPORTED ---    
Severity: normal CC: kwin-bugs-null, tobias.haase
Priority: NOR    
Version First Reported In: unspecified   
Target Milestone: ---   
Platform: Fedora RPMs   
OS: Linux   
Latest Commit: Version Fixed/Implemented In:
Sentry Crash Report:
Attachments: journalctl

Description FingerlessGloves 2025-08-31 20:27:15 UTC
Created attachment 184615 [details]
journalctl

SUMMARY
I have a Fedora 42 Laptop Lenovo L14 Gen 5 with a Ryzen 7735u CPU, and a Dell Type C Docking Station which uses MST to allow you plug in extra monitors. During boot with the kernel initramfs I can see display output on my 2 external monitors provided by the Dell Dock, when I get to SDDM the monitors stop working (no signal) and I get errors in the journal. If I unplug my laptop from the dock, I can then login using the laptop screen, once I hit the KDE desktop, I can then plug the dock back in and the screens work no problem, had no tearing, lag or video play back issues.

I'm not sure if the issue is SDDM or kwayland, I assumed kwayland since it's doing the actual displaying part of it, and kwin_wayland_drm is doing most of the complaining.

STEPS TO REPRODUCE
1. Install Fedora 42 and fully update the system
2. Connect to a docking station which uses MST to provide multiple monitors over one Type C cable. Not to be mistaken with DisplayLink based docks. Dell WD19 for example.
3. Reboot
4. External screen(s) work during initramfs, but soon as you hit SDDM they turn off.

OBSERVED RESULT
Monitors turn off and won't come on. I've tried different situations to workout where the problem is, soon as I use a display that uses Displayport MST, the problem happens, directly using HDMI or even a DisplayLink dock the problem doesn't happen.

I've tried two monitors and single monitors through the Dock.

If I SSH the laptop while it's in the broken state, I can see in /sys/ the monitors are there with a status of connected.

EXPECTED RESULT
Screen to function as normal, as they do in the wayland desktop.

SOFTWARE/OS VERSIONS
Operating System: Fedora Linux 42
KDE Plasma Version: 6.4.4
KDE Frameworks Version: 6.17.0
Qt Version: 6.9.1
Kernel Version: 6.16.3-200.fc42.x86_64 (64-bit)

ADDITIONAL INFORMATION
Please see attachment for logs.