SUMMARY Plasma/Wayland doesn't recognize external display on reconnected USB-C dock. STEPS TO REPRODUCE 1. Use a type-c USB w/ alt mode laptop and a dock (like Dell WD15) 2. Log in to Plasma Wayland from SDDM with the dock connected, see external screen work right 3. Disconnect the dock, reconnect some time later OBSERVED RESULT External screen doesn't activate (but everything else does, e.g. sound, USB devices, ethernet work well on reconnect) EXPECTED RESULT Screen should be identified and turned on SOFTWARE/OS VERSIONS Operating System: KDE neon Unstable Edition KDE Plasma Version: 5.16.80 KDE Frameworks Version: 5.62.0 Qt Version: 5.12.3 Kernel Version: 5.2.0-050200rc7-generic OS Type: 64-bit Processors: 12 × Intel® Core™ i7-8750H CPU @ 2.20GHz Memory: 15.4 GiB of RAM ADDITIONAL INFORMATION - This works on both Plasma/X11 and Gnome/Wayland. - As far as I can tell, docks generally use DP MST to connect multiple displays, even HDMI connection is served via DP MST. So this might be an MST-specific issue (reconnecting works with direct HDMI on the laptop) - Tested with Intel gfx - I see the port appear on /sys/class/drm/card0-DP-6 $ cat /sys/class/drm/card0-DP-2/status connected $ cat /sys/class/drm/card0-DP-2/enabled disabled It seems that the display never gets enabled, even though it's found. While searching for a bug report on this, I only found a forum entry - same story, but with HP laptop + dock: https://forum.kde.org/viewtopic.php?f=111&t=156876
Looks like an identical ticket was created, and got the attention: https://bugs.kde.org/show_bug.cgi?id=419061 *** This bug has been marked as a duplicate of bug 419061 ***