External monitor on screen dim loops between power off and on with "no signal detected"
Affected version
GNOME Shell 3.38.1 on X.org (running on Ubuntu, Wayland not tested yet) mutter: 3.38.1-2ubuntu1 gnome-shell: 3.38.1-1ubuntu1.1
Bug summary
With an external monitor plugged in (by HDMI, in my case), when the screen dims after inactivity (if set), the screen fades as expected, and eventually the [external] monitor turns off. However, when it does, the monitor instantly turns back on, reports "No Signal" promptly after, and turns off. Turns on again, reports "No Signal", turns off and so on in an endless loop, until you move the mouse to show the lock screen (or the shell, if Automatic Screen Lock is disabled or hasn't kicked in yet).
This occurred on Intel Graphics on X.org in both "Single Display" mode and "Join Displays" I happen to use an Intel i5-10210U (10th Gen, Comet Lake) in my case.
Interestingly I was unable to find this anywhere else on the internet, not here or not on the Ubuntu bug. Maybe I was using wrong terms, or maybe it's my bizarre setup.
Steps to reproduce
- Plug in an external monitor I guess.
- Ensure that GNOME in "Power" settings has "Blank screen" set to something, like 1 minute for convenience.
- Wait for the screen to fully dim.
- Experience the bug.
What happened
The external monitor started switching between the sleep state and source detecting state, but ended up failing with "No Source" in an endless loop.
What did you expect to happen
The external monitor to stay in the sleep state.
Relevant logs, screenshots, screencasts etc.
I'm including a recording demonstrating the issue.
thebug
If it is of any help, here are the last lines from journalctl -r
. The screen fade started at 22:14:05.
sty 03 22:12:57 acer systemd[1]: sys-devices-virtual-misc-vmbus\x21hv_kvp.device: Job sys-devices-virtual-misc-vmbus\x21hv_kvp.device/start failed with result 'timeout'.
sty 03 22:14:28 acer dbus-daemon[801]: [system] Activating via systemd: service name='net.reactivated.Fprint' unit='fprintd.service' requested by ':1.79' (uid=1000 pid=2303 comm="/usr/bin/gnome-shell " label="unconfined")
sty 03 22:14:28 acer systemd[1]: Starting Fingerprint Authentication Daemon...
sty 03 22:14:28 acer dbus-daemon[801]: [system] Successfully activated service 'net.reactivated.Fprint'
sty 03 22:14:28 acer systemd[1]: Started Fingerprint Authentication Daemon.
sty 03 22:14:28 acer NetworkManager[803]: <info> [1609708468.9197] agent-manager: agent[8acc9f8c312ab139,:1.79/org.gnome.Shell.NetworkAgent/1000]: agent registered