I have a Lenovo monitor connected to my laptop via HDMI, which mostly works well except for this one problem:
KDE Plasma > System Settings > turn off screen after 10 minutes
when the screen turns off, after about 10 seconds the monitor starts auto-cycling through input sources
this triggers my laptop screen to briefly turn back on, which then turns my external monitor back on
I’ve seen occasional references to this issue on various other forums. The solution seems to be to disable auto input select on the monitor itself, but my monitor doesn’t have that setting. (I’ve also seen references to stopping/disabling kscreen_backend_launcher but I don’t seem to have that process running.)
This same problem occurred when I previously had Linux Mint with Cinnamon installed. But a few months ago, I switched to CachyOS with KDE Plasma, and the problem didn’t occur with that setup, until recently:
It started happening on CachyOS when the linux-cachyos kernel moved from 6.18 to 6.19 (I think)
I switched back to the linux-cachyos-lts kernel (6.18 at the time) and it stopped for a couple of weeks
It started happening again a few weeks ago after a minor kernel upgrade, and now it happens on 6.18 and 6.19
Previously on Mint, switching kernels also seemed to have some effect on this behaviour (but it never fully went away until switching to CachyOS)
I’m not sure exactly what changed to cause this, so I’m not even sure where I could post a bug report. I have no idea whether it is a kernel issue, but there was a brief period where using KDE Plasma made it go away. Anyone have any ideas or suggestions? How might I go about tracking down the specific thing that changed to break this again? Thanks for any help.
The output of inxi -aG will give us the monitor model etc for troubleshooting. But it may be a limitation/glitch in how the monitor interprets input. Can you use displayport instead of HDMI? It will likely give better results as well as increased performance (which has nothing to do with your problem), but may also handle power modes better.
Thanks for the reply! It is 100% a problem with this monitor, but it was working perfectly until a couple of weeks ago. Sadly, for uninteresting & unrelated reasons, I can’t use any connection other than HDMI.
Here’s the output of inxi -aG in case it’s useful:
Make sure DDC/CI is enabled on the monitor. From the manual:
Using the direct access controls
The direct access controls can be used when the On Screen Display (OSD) is not displayed.
Table 2-1. Direct access controls
Icon Control Description
3
Input Source Switches the video input source.
Shift back to previous level when in OSD mode.
DDC-CI Press and hold for 10 seconds to enable or
disable the DDC-CI function.
Exit Exit and return to previous level.
I’ve tried all of the OSD monitor settings and none of them seem to have an effect on this problem. And I didn’t change any monitor settings before when the problem began happening recently.
It’s clear that once the screen is turned off by the laptop, the monitor waits five to ten seconds and then begins cycling through input sources looking for a signal. When it lands back on the HDMI input, the laptop reads that as a hotplug event (as though an HDMI monitor had just been plugged in) and turns the screen back on.
As I said, this was previously happening on Mint, but then didn’t happen on CachyOS with KDE Plasma, but then only recently began happening again. (It would be great to know if this might be caused by a kernel upgrade, or some piece of KDE software, so that I could figure out where to file a bug report.)
It’s more likely to be a monitor issue. i.e. what its behaviour is when it doesn’t detect a signal from the PC. In your case it seem to go looking for a signal on all available inputs presumably until it finds one.
It could be a linux/software change for example if the system was sending a connection signal but had instructed the monitor to sleep; but some update or change (power management perhaps) changed that behaviour so no signal is sent (would make sense for a laptop because it wants to conserve as much power as possible).
What does fwupdmgr get-history show? Just wondering if the firmware on your monitor was recently updated.
fwupdmgr get-history shows No history. This monitor hasn’t had a firmware update available for a few years now.
Seems like there must be a difference between the two hotplug events (monitor turned on normally vs monitor connected due to auto-switching inputs), because at some point these were handled differently by the laptop. But some software change seems to now treat those as being the same event. I’ve tried looking into trying to change that with udev, but everything I’ve read indicates it’s handled at some deeper kernel/bios level that I can’t really change with some external script or something.
