Public bug reported:
## Summary
External display via USB-C DP Alt Mode causes continuous "Page flip failed:
drmModeAtomicCommit: Invalid argument" errors in GNOME Shell, making the
display unusable despite kernel correctly detecting it.
## Hardware
- Lenovo ThinkPad T14s Gen 6 (Snapdragon X Elite / X1E78100)
- External display: Samsung QBQ90 43" TV via Anker USB-C dock (DP Alt Mode)
## Software
- Ubuntu (questing)
- Kernel: 6.18.0-9-qcom-x1e (also reproduced on 6.18.2-nostubble)
- GNOME Shell: 49.0
- Mutter: 49.0
## Symptoms
1. External display is detected correctly by kernel
2. EDID reads successfully
3. Display works on TTY (Ctrl+Alt+F3)
4. Display shows output during shutdown/reboot
5. GNOME Shell fails with atomic modeset errors
6. gnome-shell hangs when display is connected
## Evidence
- `cat /sys/class/drm/card1-DP-2/status` → connected
- `cat /sys/class/drm/card1-DP-2/enabled` → disabled
- EDID valid (hexdump shows Samsung data)
- Modes available in /sys/class/drm/card1-DP-2/modes
## Journal errors
```
Page flip failed: drmModeAtomicCommit: Invalid argument
```
(repeats continuously)
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/2137256
Title:
[X1E78100] Page flip failed: drmModeAtomicCommit: Invalid argument
with external display on ThinkPad T14s
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