https://bugs.kde.org/show_bug.cgi?id=489945
Bug ID: 489945
Summary: Wayland compositor (sometimes) outputs corrupted video
signal to one of two external monitors
Classification: Plasma
Product: kwin
Version: unspecified
Platform: unspecified
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: wayland-generic
Assignee: kwin-bugs-n...@kde.org
Reporter: len...@gmail.com
Target Milestone: ---
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SUMMARY
When using kwin_wayland and plugging in a USB4 docking station with two UHD
monitors, the video to one of the monitors is often corrupted. Switching to an
x11 display and then back fixes this corruption. (Works fine with Thunderbolt
hardware.)
STEPS TO REPRODUCE
1. Boot up and login to kwin_wayland without a docking station attached
2. Detach power from docking station, reattach power. (This is important, as it
seems to change some mode in the docking station - this could indicate that the
bug is in the docking station software - see Additional Information below)
3. Attach a docking station with two 3840x2160 resolution monitors in
DisplayPort mode
OBSERVED RESULT
Corrupted video signal to the monitor designated on the "second" DisplayPort
port
EXPECTED RESULT
Normal video
SOFTWARE/OS VERSIONS
Operating System: KDE neon 6.0
KDE Plasma Version: 6.1.3
KDE Frameworks Version: 6.4.0
Qt Version: 6.7.0
Kernel Version: 6.8.0-36-generic (64-bit)
Graphics Platform: Wayland
Processors: 16 × AMD Ryzen 7 7840U w/ Radeon 780M Graphics
Memory: 60.6 GiB of RAM
Graphics Processor: AMD Radeon Graphics
Manufacturer: Framework
Product Name: Laptop 13 (AMD Ryzen 7040Series)
System Version: A7
Docking Station: Anker 568 USB Docking Station, product number A8399
(https://www.anker.com/products/a8399?variant=42385578393750)
ADDITIONAL INFORMATION
Workaround: Start an X11 session (even as simply as using Plasma's "switch
user" button) with the dock plugged in
The docking station in question contains a VIA Labs USB4 hub. I've tested the
following hardware combinations:
AMD Framework laptop:
- Works with X11 or after an X11 session
- Produces a corrupted signal when the first plugin after the dock goes to
sleep or is powered on.
Intel Framework laptop (12th generation):
- Works properly with kwin_wayland
- Works properly with X11
Macbook (M1) running macOS:
- Works as expected, with known Apple silicon mac limitation of the external
display rendering the same image (but not corrupted)
Steam Deck:
- Works as expected in desktop mode (which uses X11)
I recognise that this bug may well be somewhere other than kwin_wayland.
However, there appears to be something being done in x11 that works around this
problem until the dock goes to sleep, so I'm hopeful that not only can
kwin_wayland implement this workaround, but that also the expertise here can
help point me to the proper place to file any other relevant bug reports.
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