[i915] external monitor goes black for several seconds at a time, randomly

Thanks for the bug report. Issues like this are almost always caused by a bad cable, bad connection, or by using intermediate adapters. So ideally please try a new cable.

Also, next time the problem happens please then run:

  journalctl -b0 > journal.txt

and attach the resulting text file here.

(Recently,) it only happens when I make something full-screen on the external monitor. I do not think this is a hardware (which is brand new) problem.
Just now I made a browser full screen and it immediately strted happening every several seconds for a couple of seconds at a time. I've attached the journal

Thanks for the log. There doesn't seem to be anything relevant there, at least not for the past few days. So it seems like the kernel isn't aware of the problem.

Indeed this looks like a bad cable or bad connection somewhere. Especially if fullscreening a window triggered the problem -- that suggests there's a bandwidth limit being exceeded, caused by a hardware problem. Most likely the cable or one of its connections, but there's a slim chance the monitor itself or even the laptop is faulty and unable to maintain a stable link at 4K 60Hz.

P.S. The monitor is not "a very popular Samsung one". It appears to be an Acer B326HK.

Ah, it appears you've tried both an Acer B326HK (Xrandr.txt) and a Samsung U32J59x (XorgLog.txt). If you experience similar problems with both then it suggests the problem is not the monitor but the cable, connectors, adapters (if any) or the laptop.

Thank you so much, Daniel!
The Samsung is new. I'll try some swapping to isolate any hardware problem.

You mentioned "intermediate adapters". I'm using a Lenovo Ultradock between my laptop and the monitor.
 This causes no trouble on my Acer B326HK, which is just as high-res, but the new Samsung monitor continues to do the blackout thing. It's not strictly reproducible so far (fullscreening does not always cause any problem, and is not required to cause the problem).

Happily, I have two ultradocks. It happens with both! And the brand new HDMI cable looks fine.

I cannot try without the ultradock because my laptop does not have an HDMI port.

No one else has reported this problem, though if it's a hardware fault with the monitor (my interpretation) then it might be rare. I have recently upgraded to 21.04 and Wayland.

I am wondering:
Should I buy an adapter from HDMI to VGA, if such a thing exist?

You would be generous to give this any more attention. Thank you!

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No one else has joined this bug, but it has continued to make life with my expensive monitor extremely annoying.

And despite suggestions above, I am certain this is not a hardware problem.

Here is new proof:
 yesterday, I initiated an upgrade (do-release-upgrade) to 22.04 from 21.10 from the command line.
By chance, I tried full-screening a video while the upgrade was in progress. Amazingly, it worked flawlessly the entire duration of the upgrade! ! !
 As soon as it was done and rebooted, I tried playing that video again and it did the black-screen / device searching every 3 seconds or so, as it always has.

So, how can I reproduce the thing that the upgrade did?! It said something at the beginning about disabling screen lock or something like that, but I have tried turning off all such things in my settings already.

I ran into the same bug on the weekend as I tried to upgrade my monitor. In my case it was that Intel GPUs could not sustain a stable signal to a high-end monitor. Even though my setup was within range of HBR3, I could only maintain a stable DisplayPort HBR3 signal plugged it into an Nvidia card, not with Intel. With Intel the monitor would go black during large or rapid screen changes.

Three possible workarounds come to mind:

  * Use DisplayPort or USB-C if available. They're more likely to achieve high bandwidth than HDMI, typically.

  * Use a lower refresh rate (worked in my case).

  * Ask developers to implement the "max bpc" connector property exposed by the i915 kernel driver.

That last one is already available in Xorg via:

  xrandr --output NAME --set "max bpc" 8

See also bug 1975872

Wow, I think this line (comment #10 from @vanvugt)

xrandr --output NAME --set "max bpc" 8

works for me!

If it's still unreliable then try 6 instead of 8, but 8 should look better.

Any other fixes? xrandr isn't working, with Wayland; Running 22.10 on my machine, and this is problematic with 4k or ultrawide displays especially

I feel your pain, having suffered the same issue just a few seconds ago. Although there's a chance we're seeing the same symptoms with different root causes so please be sure to open your own bug by running:

  ubuntu-bug linux

Start by testing different display cables/connection types.

"Fix released" for mutter 43.0 only because a workaround was added, which you can configure in ~/.config/monitors.xml as

      <monitor>
        ...
        <maxbpc>8</maxbpc>
      </monitor>

But it may not help everyone. It didn't solve my issues. And so the bug is still open for the Linux kernel.

My issue with Intel 12th gen regularly losing display signal *appears* to be fixed by using kernel 6.1. Fingers crossed it stays fixed.