I have been using an external monitor on my notebook (Lenovo Thinkpad P50)
under openSUSE Tumbleweed) for years. However, this has now come to an abrupt
end. In the middle of an X11 session, at the same moment I started a (third)
VLC instance, the external monitor went dark and all windows of my X11 session
were moved to the internal notebook screen.

The external monitor was, and still is, not recognized by the machine, not even
after a reboot. This does not only happen on the X11 level, but already further
down on a lower level. The ���������inxi��������� command only shows the internal monitor, no
longer the external one. Udev correctly creates all the devices for all the
display ports of the notebook, but when I connect the external monitor to the
HDMI-1 port, the kernel does not create a uevent. Consequently, no udev event
is issued, both according to ���������udevadm monitor���������.

Here are the devices and their states:
/sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-DP-1/status: disconnected
/sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-DP-2/status: disconnected
/sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-HDMI-A-1/status:
disconnected
/sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-HDMI-A-2/status:
disconnected
/sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-eDP-1/status: connected


Yet, in an X11 session, the notebook somehow recognizes that a monitor is
connected: An OSD screen is displayed asking how to configure the new monitor.
Clicking on any of the alternatives has no effect, however.

I am ruling out any hardware error. Why? Because the external monitor works
fine on a second notebook. And when I boot a Linux live system on my first
notebook, the external monitor is recognized and used without any problems. On
the other hand, if I use my notebook with the actual operating system with a
different external monitor, it doesn���������t work either.

I test booted the older kernel version 6.1.1 instead of the (as of this
writing) current 6.1.8 kernel. I also tried an older version of the i915
driver. Both measures showed no effect.

Now I ran out of ideas what else to try or where else to look. And as far as I
am aware of, the status of connected hardware isn���������t stored anywhere where it
survives a reboot ��������� or is it?