Screen sometimes black; how to debug?

Desktop Environments Plasma
1

I’ve got Nvidia, Wayland and Plasma. I have a two-monitor setup (an old, small, reliable Dell, and a big 4K Samsung Odyssey that’s a slow, unreliable piece of crap), but I frequently switch the Samsung between my PC and my Macbook. It works fine with the Macbook. The PC (EndeavourOS) and the monitor itself frequently get confused about this in various ways.

At the moment, the Samsung is just black, but EndeavourOS thinks it exists, and considers it the main display, so I don’t have access to my task bar, and many apps open on the screen that doesn’t exist.

The weird thing is that unplugging the hdmi cable doesn’t change anything. It’s currently unplugged, but EndeavourOS still thinks it’s there. When I plug it in, the monitor still says it’s not getting a signal.

This doesn’t happen often, but when it does, it’s super annoying. Rebooting will probably fix this, but is there a way to fix it without rebooting? Is there a way to debug what’s going on? Is there a way to prevent it from happening at all?

I don’t mind debugging this issue myself, but I have no idea where to start.

2

A few things I already figured out:

kscreen-doctor --outputs

gives me a thorough list of stats on my two screens. The ID at the top can be used to do things like:

kscreen-doctor output.<ID>.disable

which disables the nonfunctional screen and automatically turns the remaining screen into the primary. That can also be done manually with something like

kscreen-doctor output.<ID>.primary

but that’s apparently not necessary.

I’ve not yet succeed in turning on the broken screen. Apparently the problem is that Nvidia driver end up in a broken state and refuses to fix it. Not sure yet how to get it out of that state and start treating the screen normally again.

3

How long your pc running without reboot?
You can reload nvidia module for sure but uh.

And you sure your pc hdmi port is not broken?

4

can you create a new user account on the system and see if your able to get access to the monitor?

5

And how long ago sinse last update?

6

I think my last system update was a month ago. My last reboot may have been more recent, but I don’t reboot often. (I’m of the opinion that a system should be stable without reboots, but not every OS agrees.)

I see there are new updates for kwin and nvidia drivers, so there’s definitely the possibility that those contain a fix for this. My understanding so far is that this bug is a known Nvidia hdmi issue.