https://bugs.kde.org/show_bug.cgi?id=419061
Bug ID: 419061
Summary: Display hot plug not working in Wayland
Product: kwin
Version: git master
Platform: Other
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: wayland-generic
Assignee: kwin-bugs-n...@kde.org
Reporter: dan...@lbe.rs
Target Milestone: ---
Created attachment 126917
--> https://bugs.kde.org/attachment.cgi?id=126917&action=edit
Log with QT_LOGGING_RULES="kwin_*.debug=true" and LIBGL_DEBUG=verbose
SUMMARY
When plugging in an external display via USB-C/Thunderbolt hub (display
connected via DisplayPort to it) to my Dell XPS 9370, KWin does not activate
the display.
When starting KWin with the display already connected, it works fine.
Hot plugging works fine in other compositors like Sway.
Udev events are triggered reliably and KWin sees them.
It tried stepping through without being very familiar with the code or libdrm.
The issue seems to be, that in DrmBackend::updateOutputs() the
con->isConnected() check fails, because libdrm always returns a device with
connection == DRM_MODE_DISCONNECTED.
I don't know yet how this differs from e.g. Sway.
STEPS TO REPRODUCE
1. Connect external display via USB-C/Thunderbolt hub to XPS 9370
2. startplasma-wayland --xwayland --drm
3. Everything works fine
4. Disconnect external display
5. KWin correctly updates display configuration to a single dispaly
6. Reconnect external display
OBSERVED RESULT
Nothing happens.
EXPECTED RESULT
KWin updates display configuration back to two displays.
SOFTWARE/OS VERSIONS
Operating System: Arch Linux
KDE Plasma Version: 5.18.3
KDE Frameworks Version: 5.68.0
Qt Version: 5.14.1
Kernel Version: 5.5.9-arch1-2
OS Type: 64-bit
Processors: 8 × Intel® Core™ i7-8550U CPU @ 1.80GHz
Memory: 15,3 GiB of RAM
OpenGL vendor string: Intel Open Source Technology Center
OpenGL renderer string: Mesa DRI Intel(R) UHD Graphics 620
(Kabylake GT2)
OpenGL version string: 4.6 (Core Profile) Mesa 19.3.4
OpenGL shading language version string: 4.60
Driver: Intel
GPU class: Unknown
OpenGL version: 4.6
GLSL version: 4.60
Mesa version: 19.3.4
Linux kernel version: 5.5.9
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