Bug 403438

Summary:	External monitor connected through displayport <-> HDMI is not detected in Plasma Wayland
Product:	[Plasma] kwin	Reporter:	Dan G <dgllghr>
Component:	platform-drm	Assignee:	KWin default assignee <kwin-bugs-null>
Status:	RESOLVED NOT A BUG
Severity:	normal
Priority:	NOR
Version First Reported In:	5.14.5
Target Milestone:	---
Platform:	Manjaro
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:
Attachments:	Xorg.0.log

Description Dan G 2019-01-20 18:34:07 UTC

SUMMARY

My laptop (unfortunately) only has USB-3/displayport ports and my external monitor doesn't have displayport. With Plasma on X, I can connect the monitor with an HDMI <-> USB3 dongle and the monitor works fine. When I switch to the Wayland session in Plasma and connect my monitor the same way, the external monitor is not detected. My laptop is a Dell XPS 9575 if that is helpful at all.

STEPS TO REPRODUCE
1. Log into Plasma X session
2. Connect external monitor using HDMI<->USB3 dongle so that the monitor is connected to HDMI and the computer is connected to displayport
3. Popup appears with options to extend, mirror, etc. and monitor is visible in System Settings -> Displays
4. Log out and log in to Plasma Wayland session
5. Connect external monitor using dongle (the same monitor and cables as before)

OBSERVED RESULT
No external monitor popup is shown and monitor does not appear in System Settings -> Displays

EXPECTED RESULT
Monitor shows up in System Settings -> Displays and can be used as part of the display

SOFTWARE/OS VERSIONS
Windows: 
MacOS: 
Linux/KDE Plasma: Manjaro
(available in About System)
KDE Plasma Version: 5.14.5
KDE Frameworks Version: 5.54
Qt Version: 5.12.0

ADDITIONAL INFORMATION

Comment 1 Martin Flöser 2019-01-20 19:29:32 UTC

Could you please attach your /car/log/Xorg.0.log from working X session?

Comment 2 Dan G 2019-01-21 14:59:06 UTC

Created attachment 117595 [details]
Xorg.0.log

Comment 3 Martin Flöser 2019-01-21 16:37:03 UTC

According to the log you have both an Intel and amd gpu. Do you know which one is connected to your USB port? I assume it's the amd one.

Comment 4 Dan G 2019-01-21 16:50:19 UTC

When I connect the same external monitor with the same configuration on Windows, it says that the monitor is connected to the Intel card (HD Graphics 630)

Comment 5 Dan G 2019-05-27 15:35:05 UTC

I discovered that the two USB-C ports I was using to plug in the monitor might have problems. They are both part of the same board, and I suspect that the board is damaged in some way. When I plugged in the monitor to the ports on the other side of the laptop, it worked as expected in the Wayland session. I don't know why KDE on X was able to use the external monitor, but I have a theory.

I discovered that the USB-C ports that I was using originally might have a problem because I was unable to output sound over HDMI. However, when I tried the ports on the other side of the laptop, the sound output worked fine. My theory is the the wayland session is depending on something to do with sound output, and when that fails it then won't output the video. But on KDE on X, it will happily output video regardless of sound.

This is very much just a theory based on what I have observed. But my feeling is that this really isn't a bug but a hardware problem with my machine. I thought I would include the additional information in case it was of interest in some way. Please feel free to close this issue.