[kde] [Bug 475978] New: External monitor loses signal when connected to USB-C dock using wayland with recent AMD APUs

[Sam]

https://bugs.kde.org/show_bug.cgi?id=475978

            Bug ID: 475978
           Summary: External monitor loses signal when connected to USB-C
                    dock using wayland with recent AMD APUs
    Classification: I don't know
           Product: kde
           Version: unspecified
          Platform: Fedora RPMs
                OS: Linux
            Status: REPORTED
          Severity: normal
          Priority: NOR
         Component: general
          Assignee: unassigned-bugs at kde.org
          Reporter: accountsverify at hotmail.com
  Target Milestone: ---

Created attachment 162503
  --> https://bugs.kde.org/attachment.cgi?id=162503&action=edit
Framework 13 dmesg

SUMMARY
***
When using Wayland, both SDDM and the plasma desktop will immediately cause my
external monitor to lose all signal when connected through a USB-C dock. Once
it has lost signal this way, it will not recover without rebooting the laptop.
While signal is gone, the monitor still shows up in display manager as though
it were still connected, and the laptop screen still registers as the secondary
display. I have seen this behavior now with 2 laptops, one with an Nvidia GPU
and one without a dGPU (Asus x13 - 6900HS + 3050ti, Framework 13 - 7840U). The
Asus laptop runs Fedora 38 KDE spin, the Framework is running Fedora 39 Beta
with KDE installed alongside gnome. The dock is a lenovo universal USB-C dock.
If I use Gnome instead of plasma, display output shows as expected even with
Wayland.

KDE/SDDM + X11 + dock = works
Gnome + wayland + dock = works
KDE/SDDM + wayland + direct cable to monitor = works
KDE/SDDM + wayland + dock = display output immediately lost
***


STEPS TO REPRODUCE
1. USB-C dock connects to monitor via HDMI
2. USB-C port with DP alt mode connects from laptop to dock (I have only tested
with recent model AMD APUs using RDNA3 based iGPUs - unsure if this is required
condition)
3. Attempt to render either SDDM or plasma desktop using Wayland

OBSERVED RESULT
External monitor loses signal completely, but still shows up in display
settings. Display signal will not restore until laptop is rebooted.

EXPECTED RESULT
External monitor displays SDDM or plasma desktop.


SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: Seen on both Fedora 38 KDE spin (kernel 6.5.7-200) and Fedora
39 Beta (Kernel 6.5.7-300, although this behavior is not new and has been
present with older kernels)
(available in About System)
KDE Plasma Version: 5.27.8
KDE Frameworks Version: 5.110.0
Qt Version: 5.15.10

ADDITIONAL INFORMATION

After monitor loses signal, I get trace output in dmesg on both laptops which I
am attaching.

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