Second Monitor suddenly not working anymore

Help
1

I’ve been using two monitors for a really long time now. After a reboot (a couple of days ago) the second monitor is not working anymore.

  • I am currently on plasmashell 5.27.3
  • Both monitors work till I login
  • The login-screen is still shown on both monitors
  • Did not change anything physically before this happened
  • One monitor is connected via HDMI and one via display-port
  • In the display and monitor tab in the settings “An output has been removed. Settings have been reloaded”/“A new output has been added. Settings have been reloaded.” flash every 2 or 3 seconds.
  • Is the same for Wayland and X11 protocols
  • I am running Arch Linux
  • Running other DE installations it works just fine (e.g. this arch installation with gnome)
  • I have found this My second monitor stops working after login. • KDE Community Forums related post, which is left without an answer.

How do I go about debugging this? What is the most efficient way of finding the issue?
Thank you in advance.

2

Run kscreen-console monitor and see if that tells us anything is happening

3

Similar behavior to the one described in the settings. The monitor logs “Properties changed” every 2-4 seconds. “disconnected disabled priority 0” changes to “connected disabled priority 0” and back (actually it logs every property twice before logging its counterpart).

One line of the monitor:

Priorities changed: QMap((84, KScreen::Output(84, "DisplayPort-0", disconnected disabled priority 0, pos: QPoint(0,0), res: QSize(-1, -1), modeId: "", scale: 1, clone: no, rotation: KScreen::Output::None, followPreferredMode: false))(85, KScreen::Output(85, "DisplayPort-1", connected enabled priority 1, pos: QPoint(0,0), res: QSize(1920, 1080), modeId: "90", scale: 1, clone: no, rotation: KScreen::Output::None, followPreferredMode: false))(86, KScreen::Output(86, "DisplayPort-2", disconnected disabled priority 0, pos: QPoint(0,0), res: QSize(-1, -1), modeId: "", scale: 1, clone: no, rotation: KScreen::Output::None, followPreferredMode: false))(87, KScreen::Output(87, "HDMI-A-0", disconnected disabled priority 0, pos: QPoint(0,0), res: QSize(-1, -1), modeId: "", scale: 1, clone: no, rotation: KScreen::Output::None, followPreferredMode: false)))
4

ok, so we’ll keep going deeper down the stack:

Can you run:
sudo udevadm monitor

and get a snapshot of events (or lack of events)

5 
[<me>@arch ~]$  sudo udevadm monitor
[sudo] password for <me>: 
monitor will print the received events for:
UDEV - the event which udev sends out after rule processing
KERNEL - the kernel uevent

KERNEL[1840.231895] change   /devices/pci0000:00/0000:00:03.1/0000:07:00.0/0000:08:00.0/0000:09:00.0/drm/card0 (drm)
UDEV  [1840.236876] change   /devices/pci0000:00/0000:00:03.1/0000:07:00.0/0000:08:00.0/0000:09:00.0/drm/card0 (drm)
KERNEL[1841.307124] change   /devices/pci0000:00/0000:00:03.1/0000:07:00.0/0000:08:00.0/0000:09:00.0/drm/card0 (drm)
UDEV  [1841.310658] change   /devices/pci0000:00/0000:00:03.1/0000:07:00.0/0000:08:00.0/0000:09:00.0/drm/card0 (drm)
KERNEL[1849.492320] change   /devices/pci0000:00/0000:00:03.1/0000:07:00.0/0000:08:00.0/0000:09:00.0/drm/card0 (drm)
UDEV  [1849.498961] change   /devices/pci0000:00/0000:00:03.1/0000:07:00.0/0000:08:00.0/0000:09:00.0/drm/card0 (drm)
KERNEL[1850.567262] change   /devices/pci0000:00/0000:00:03.1/0000:07:00.0/0000:08:00.0/0000:09:00.0/drm/card0 (drm)
UDEV  [1850.570858] change   /devices/pci0000:00/0000:00:03.1/0000:07:00.0/0000:08:00.0/0000:09:00.0/drm/card0 (drm)
KERNEL[1858.752397] change   /devices/pci0000:00/0000:00:03.1/0000:07:00.0/0000:08:00.0/0000:09:00.0/drm/card0 (drm)
UDEV  [1858.758412] change   /devices/pci0000:00/0000:00:03.1/0000:07:00.0/0000:08:00.0/0000:09:00.0/drm/card0 (drm)
KERNEL[1859.817439] change   /devices/pci0000:00/0000:00:03.1/0000:07:00.0/0000:08:00.0/0000:09:00.0/drm/card0 (drm)
UDEV  [1859.820739] change   /devices/pci0000:00/0000:00:03.1/0000:07:00.0/0000:08:00.0/0000:09:00.0/drm/card0 (drm)
KERNEL[1868.002520] change   /devices/pci0000:00/0000:00:03.1/0000:07:00.0/0000:08:00.0/0000:09:00.0/drm/card0 (drm)
UDEV  [1868.008818] change   /devices/pci0000:00/0000:00:03.1/0000:07:00.0/0000:08:00.0/0000:09:00.0/drm/card0 (drm)
KERNEL[1869.077623] change   /devices/pci0000:00/0000:00:03.1/0000:07:00.0/0000:08:00.0/0000:09:00.0/drm/card0 (drm)
UDEV  [1869.081004] change   /devices/pci0000:00/0000:00:03.1/0000:07:00.0/0000:08:00.0/0000:09:00.0/drm/card0 (drm)
KERNEL[1877.262776] change   /devices/pci0000:00/0000:00:03.1/0000:07:00.0/0000:08:00.0/0000:09:00.0/drm/card0 (drm)
UDEV  [1877.269200] change   /devices/pci0000:00/0000:00:03.1/0000:07:00.0/0000:08:00.0/0000:09:00.0/drm/card0 (drm)
KERNEL[1878.328430] change   /devices/pci0000:00/0000:00:03.1/0000:07:00.0/0000:08:00.0/0000:09:00.0/drm/card0 (drm)
UDEV  [1878.331292] change   /devices/pci0000:00/0000:00:03.1/0000:07:00.0/0000:08:00.0/0000:09:00.0/drm/card0 (drm)
KERNEL[1886.522786] change   /devices/pci0000:00/0000:00:03.1/0000:07:00.0/0000:08:00.0/0000:09:00.0/drm/card0 (drm)
UDEV  [1886.529497] change   /devices/pci0000:00/0000:00:03.1/0000:07:00.0/0000:08:00.0/0000:09:00.0/drm/card0 (drm)
KERNEL[1887.588141] change   /devices/pci0000:00/0000:00:03.1/0000:07:00.0/0000:08:00.0/0000:09:00.0/drm/card0 (drm)
UDEV  [1887.591693] change   /devices/pci0000:00/0000:00:03.1/0000:07:00.0/0000:08:00.0/0000:09:00.0/drm/card0 (drm)