https://bugs.kde.org/show_bug.cgi?id=522580
Bug ID: 522580
Summary: after SDDM do not forward DRM master
Classification: Plasma
Product: kwin
Version First 6.7.0
Reported In:
Platform: Neon
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: compositing
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: ---
Created attachment 193987
--> https://bugs.kde.org/attachment.cgi?id=193987&action=edit
auto-generated by CLAUDE via SSH , because i can't see anything into MONITOR
(until RE-BOOT)
## Issue 2 — SDDM Xorg greeter does not release DRM master on the display GPU
at login → black screen / "no signal" (multi-GPU, display on secondary GPU)
**Component:** `sddm` (or `kwin` DRM master handoff / `systemd-logind` VT
release)
### Summary
Because the only display is connected to the **integrated Vega APU**
(`card2-HDMI-A-2`) and
SDDM uses an **Xorg greeter**, the greeter's `Xorg` process acquires DRM master
on `card2`.
On login, SDDM does **not** reliably stop that greeter `Xorg` / drop DRM
master, so the user's
`kwin_wayland` cannot acquire DRM master on `card2` and never enables the
connected output.
The monitor gets **no signal**; the user must re-attempt login several times
before the
greeter finally releases and kwin lights up the output.
### Steps to reproduce
1. Multi-GPU AMD system, monitor connected only to the integrated GPU's HDMI
(`/dev/dri/card2`, connector `HDMI-A-2`); discrete GPU has no display.
2. SDDM with default Xorg greeter.
3. (One reliable trigger:) disrupt the running Wayland session so SDDM re-shows
the greeter
(e.g. log out, or the session crashes as in Issue 1).
4. At the SDDM screen, log in to a Plasma Wayland session.
### Expected
Greeter `Xorg` stops, drops DRM master on `card2`; `kwin_wayland` acquires it
and enables
`HDMI-A-2` → desktop appears on first login.
### Actual
Greeter `Xorg` (root, on `vt2`) stays alive holding DRM master on `card2`:
```
$ sudo fuser -v /dev/dri/card2
/dev/dri/card2: root <PID> F...m Xorg # 'm' = DRM master, greeter
still owns it
```
`kwin_wayland` starts but logs only:
```
kwin_wayland[...]: No backend specified, automatically choosing Wayland because
WAYLAND_DISPLAY is set
```
then stalls at ~0% CPU, never enabling the output:
```
/sys/class/drm/card2-HDMI-A-2/enabled = disabled
/sys/class/drm/card2-HDMI-A-2/status = connected
```
→ monitor reports no signal. Killing the stale greeter `Xorg` lets kwin
proceed; but SDDM
may respawn the greeter, and re-login is required. After 2–3 attempts login
succeeds.
### Workaround candidates
- SDDM Wayland greeter (`DisplayServer=wayland` in `sddm.conf`) to avoid an
Xorg greeter
holding DRM master on the display GPU.
- Ensure `logind`/`drmDropMaster` is called when the greeter VT (`vt2`) is
left.
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