https://bugs.kde.org/show_bug.cgi?id=522228
Bug ID: 522228
Summary: Plasma Login Manager Wayland greeter black-screens
with three Acer XV273K V3 monitors on AMDGPU
Classification: Plasma
Product: plasma-login-manager
Version First 6.7.1
Reported In:
Platform: Gentoo Packages
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: general
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected]
Target Milestone: ---
DESCRIPTION
On my Gentoo Linux system using systemd and Plasma Login Manager, the Wayland
greeter works normally when only two monitors are connected, but the screen
goes black when all three monitors are connected at boot/login time. The
machine remains responsive; only the greeter display fails. Once the desktop
session is running, reconnecting the third monitor works correctly and the
desktop extends across all three displays as expected.
This does not appear to be tied to a specific DisplayPort connector. If any one
of the three monitors is unplugged, the greeter appears normally. If all three
are connected at startup, the greeter black-screens. Swapping the third
monitor’s cable from DisplayPort to HDMI made no difference.
STEPS TO REPRODUCE
1. Connect 3 monitors, boot to black screen
2. Unplug one, Plasma login appears
3. Alternatively reboot with just two connected, Plasma login appears
OBSERVED RESULT
With DP-1 + DP-2 connected, Plasma Login Manager starts and the greeter
appears.
With all three monitors connected, the greeter screen goes black.
If I disconnect any one of the three monitors, the greeter appears again.
If I reconnect the third monitor after the desktop is already up, all three
monitors work normally.
The issue is not specific to DP-3; it happens if any one of the three monitors
is unplugged.
Swapping the third monitor from DP to HDMI did not change the behavior.
Changing the greeter refresh rate from 160 Hz to 120 Hz did not help.
Removing the greeter’s saved output config did not help.
Using amdgpu.dc=0 changed the failure mode, but did not solve the problem.
EXPECTED RESULT
Plasma Login Manager should show the Wayland greeter normally with all three
monitors connected at boot, and it should be able to apply the saved output
configuration without black-screening.
SOFTWARE/OS VERSIONS
Operating System (available in the Info Center app, or by running `kinfo` in a
terminal window):
KDE Plasma Version: 6.7.1
KDE Frameworks Version: 6.27.0
Qt Version: 6.11.1
ADDITIONAL INFORMATION
>From journalctl -b -u plasmalogin on a failing boot:
kwin_wayland: No backend specified, automatically choosing drm
kwin_wayland_drm: No suitable DRM devices have been found
Earlier boots also showed:
kwin_core: Applying output configuration failed!
kwin_wayland_drm: atomic commit failed: Permission denied
>From kernel logs on earlier failing boots:
dpcd_set_link_settings: core_link_write_dpcd ... failed
flip_done timed out
commit wait timed out
Restoring old state failed
warnings in amdgpu_dm_atomic_commit_tail
Greeter config details
The Plasma Login Manager greeter has its own kwinoutputconfig.json under:
/var/lib/plasmalogin/.config/kwinoutputconfig.json
That file contained saved output state for the greeter user, not my normal user
account. It showed three outputs and stored modes of 3840x2160 at 160 Hz. I
changed the refresh rate to 120 Hz for testing, but that made no difference.
Deleting the file also did not fix the problem.
This looks like a Plasma Login Manager / KWin Wayland output-configuration
issue triggered by a three-monitor startup layout on AMDGPU. It does not appear
to be a general hardware failure, because the same three-monitor configuration
works once the session is established. It also does not appear to be caused by
refresh rate alone, because the monitors support 160 Hz and the issue persisted
when I changed the greeter config to 120 Hz.
If useful, I can also provide:
full journalctl -b output,
the greeter kwinoutputconfig.json,
lspci output,
or a photo of the black screen state.
Also it is worth noting that when using SDDM or GDM, it works exactly as
expected. Plymouth with BGRT fires during boot and dual-booting into Windows
has no issue.
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