I could no reproduce this issue using a laptop with a dongle and an external HDMI screen with kwin from sources.

So either this has been fixed in git compared to beta, or more probably I would guess, my setup is too different from yours (my laptop is a Dell XPS, my dongle is of brand novoo).

Could you share the `kscreen-doctor -o` and `drm_info` commands output (you will probably need to install this small utility), before and after the screen is plugged back in.

And also the content of the ~/.local/usr/share/kscreen, zipping the whole folder and attaching it here.

Created attachment 142003 [details]
Output of drm_info

Created attachment 142004 [details]
./local/kscreen

I'm also using an XPS 13 (9305), with a generic USB-C dongle that shows up in lsusb as being from Genesys Logic Inc.

---
kscreen-doctor -o
Icon theme "gnome" not found.
Output: 1 Dell Inc. DELL S2721QS/5ML3M43 enabled connected  Unknown Modes: 0:3840x2160@30! 1:3840x2160@30 2:3840x2160@25 3:3840x2160@24 4:2560x1440@60 5:1920x1080@60 6:1920x1080@60 7:1920x1080@60 8:1920x1080@60 9:1920x1080@60 10:1920x1080@50 11:1920x1080@50 12:1920x1080@25 13:1920x1080@24 14:1920x1080@24 15:1600x1200@60 16:1600x900@60 17:1280x1024@75 18:1280x1024@60 19:1152x864@75 20:1280x720@60 21:1280x720@60 22:1024x768@75 23:1024x768@60 24:800x600@75 25:800x600@60 26:720x576@50 27:720x576@50 28:720x480@60 29:720x480@60 30:720x480@60 31:720x480@60 32:640x480@75 33:640x480@60 34:640x480@60 35:640x480@60 36:720x400@70 37:3840x2160@24* Geometry: 1920,0 3202x1801 Scale: 1.19922 Rotation: 1 Overscan: 0 Vrr: incapable RgbRange:
Output: 2 DO NOT USE - AUO eDP-1-unknown enabled connected primary Panel Modes: 0:1920x1080@48 1:1920x1080@60*! Geometry: 0,720 1920x1080 Scale: 1 Rotation: 1 Overscan: 0 Vrr: incapable RgbRange: Automatic primary

Interestingly, the same issue is present if I unplug the monitor from the HDMI port on the dongle leaving the dongle plugged in, and then replug the monitor. Again, the issue isn't present under X11.

The monitor in question is a Dell S271QS.

(In reply to Tim from comment #2)
> Created attachment 142003 [details]
> Output of drm_info

That's when the screen is disconnected ?
Or is the output the same in both cases ?

Both drm-info and kscreen-doctor outputs were taken with the screen connected and working correctly. 

Happy to give outputs when disconnected or connected and not working if they will help.

Yes, do please add the output of drm_info when the output doesn't work as well. 

Could you also upload the output of "grep kwin_wayland_drm ~/.local/share/sddm/wayland-session.log" when the output doesn't work? It could also help if you set the environment variable
QT_LOGGING_RULES="kwin_wayland_drm.debug=true"
before starting the session to have the log contain some more useful information

Created attachment 142060 [details]
Output of drm_info with monitor plugged in output not working

Created attachment 142061 [details]
grep kwin_wayland_drm ~/.local/share/sddm/wayland-session.log

grep kwin_wayland_drm ~/.local/share/sddm/wayland-session.log" when the output doesn't work?

Hope I've set environment variables correctly.

--- kscreen-doctor -o - with monitor plugged in but output not working
Icon theme "gnome" not found.
Output: 1 DO NOT USE - AUO eDP-1-unknown enabled connected primary Panel Modes: 0:1920x1080@48 1:1920x1080@60*! Geometry: 0,0 1920x1080 Scale: 1 Rotation: 1 Overscan: 0 Vrr: incapable RgbRange: primary

(In reply to Tim from comment #9)
> Created attachment 142060 [details]
> Output of drm_info with monitor plugged in output not working

It shows your secondary screens (3840x2160) screen shows up in Plane 8 and CRTC 1 but not in any of its connectors which would be expected for a DisplayPort.

Kwin does try to use it but from your ` grep kwin_wayland_drm ~/.local/share/sddm/wayland-session.log ` and it seems at first there is a Connector.

```
kwin_wayland_drm: Reading output configuration for  KWin::DrmOutput(0x55abd854c110, name="eDP-1", geometry=QRect(0,0 1920x1080), scale=1)
kwin_wayland_drm: Reading output configuration for  KWin::DrmOutput(0x55abd85440d0, name="DP-3", geometry=QRect(0,0 3840x2160), scale=1)
kwin_wayland_drm: Could not find a fitting mode with size=3840x2160 and refresh rate 23975 for output DP-3
kwin_wayland_drm: Received change event for monitored drm device "/dev/dri/card0"
kwin_wayland_drm: Reading output configuration for  KWin::DrmOutput(0x55abd854c110, name="eDP-1", geometry=QRect(0,720 1920x1080), scale=1)
```
But it fails to find a mode for the screen (It would be part of its missing corresponding Connector).
Then a "change" status event happens for your GPU and the screen is not even seen detected anymore.

Adding more logs would help to figure out exactly why, a simple way to add more kwin_wayland_drm output is to edit ~/.config/QtProject/qtlogging.ini and add:

```
[Rules]
kwin_wayland_drm.debug=true
```

And exit the session reopen your session, replug you external screen.

And resend here the result of
grep kwin_wayland_drm ~/.local/share/sddm/wayland-session.log

rep kwin_wayland_drm ~/.local/share/sddm/wayland-session.log
kwin_wayland_drm: drmModeAddFB2WithModifiers is supported on GPU "/dev/dri/card0"
kwin_wayland_drm: Using Atomic Mode Setting on gpu "/dev/dri/card0"
kwin_wayland_drm: Number of planes on GPU "/dev/dri/card0" : 32
kwin_wayland_drm: Crtc 98 has properties "MODE_ID"=366, "ACTIVE"=1, "VRR_ENABLED"=0, "GAMMA_LUT"=363
kwin_wayland_drm: Crtc 167 has properties "MODE_ID"=310, "ACTIVE"=1, "VRR_ENABLED"=0, "GAMMA_LUT"=364
kwin_wayland_drm: Crtc 236 has properties "MODE_ID"=0, "ACTIVE"=0, "VRR_ENABLED"=0, "GAMMA_LUT"=0
kwin_wayland_drm: Crtc 305 has properties "MODE_ID"=0, "ACTIVE"=0, "VRR_ENABLED"=0, "GAMMA_LUT"=0
kwin_wayland_drm: EGL buffer configs count: 100
kwin_wayland_drm: Connector 308 has properties "CRTC_ID"=98, "non-desktop"=0, "DPMS"=0, "EDID"=358, "overscan"not found, "vrr_capable"=0, "underscan" not found, "underscan vborder" not found, "underscan hborder" not found, "Broadcast RGB"="Automatic"
kwin_wayland_drm: Connector 347 has properties "CRTC_ID"=167, "non-desktop"=0, "DPMS"=0, "EDID"=361, "overscan" not found, "vrr_capable"=0, "underscan" not found, "underscan vborder" not found, "underscan hborder" not found, "Broadcast RGB"="Automatic"
kwin_wayland_drm: New output on GPU "/dev/dri/card0": "DELL S2721QS/5ML3M43"
kwin_wayland_drm: New output on GPU "/dev/dri/card0": "eDP-1-unknown"
kwin_wayland_drm: Reading output configuration for  KWin::DrmOutput(0x5568aab5afd0, name="eDP-1", geometry=QRect(0,0 1920x1080), scale=1)
kwin_wayland_drm: Reading output configuration for  KWin::DrmOutput(0x5568aab5b1f0, name="DP-3", geometry=QRect(0,0 3840x2160), scale=1)
kwin_wayland_drm: Received change event for monitored drm device "/dev/dri/card0"
kwin_wayland_drm: Reading output configuration for  KWin::DrmOutput(0x5568aab5afd0, name="eDP-1", geometry=QRect(0,720 1920x1080), scale=1)

A possibly relevant merge request was started @ https://invent.kde.org/plasma/kwin/-/merge_requests/1491

(In reply to Tim from comment #13)
> rep kwin_wayland_drm ~/.local/share/sddm/wayland-session.log
> kwin_wayland_drm: drmModeAddFB2WithModifiers is supported on GPU
> "/dev/dri/card0"
> kwin_wayland_drm: Using Atomic Mode Setting on gpu "/dev/dri/card0"
> kwin_wayland_drm: Number of planes on GPU "/dev/dri/card0" : 32
> kwin_wayland_drm: Crtc 98 has properties "MODE_ID"=366, "ACTIVE"=1,
> "VRR_ENABLED"=0, "GAMMA_LUT"=363
> kwin_wayland_drm: Crtc 167 has properties "MODE_ID"=310, "ACTIVE"=1,
> "VRR_ENABLED"=0, "GAMMA_LUT"=364
> kwin_wayland_drm: Crtc 236 has properties "MODE_ID"=0, "ACTIVE"=0,
> "VRR_ENABLED"=0, "GAMMA_LUT"=0
> kwin_wayland_drm: Crtc 305 has properties "MODE_ID"=0, "ACTIVE"=0,
> "VRR_ENABLED"=0, "GAMMA_LUT"=0
> kwin_wayland_drm: EGL buffer configs count: 100
> kwin_wayland_drm: Connector 308 has properties "CRTC_ID"=98,
> "non-desktop"=0, "DPMS"=0, "EDID"=358, "overscan"not found, "vrr_capable"=0,
> "underscan" not found, "underscan vborder" not found, "underscan hborder"
> not found, "Broadcast RGB"="Automatic"
> kwin_wayland_drm: Connector 347 has properties "CRTC_ID"=167,
> "non-desktop"=0, "DPMS"=0, "EDID"=361, "overscan" not found,
> "vrr_capable"=0, "underscan" not found, "underscan vborder" not found,
> "underscan hborder" not found, "Broadcast RGB"="Automatic"
> kwin_wayland_drm: New output on GPU "/dev/dri/card0": "DELL S2721QS/5ML3M43"
> kwin_wayland_drm: New output on GPU "/dev/dri/card0": "eDP-1-unknown"
> kwin_wayland_drm: Reading output configuration for 
> KWin::DrmOutput(0x5568aab5afd0, name="eDP-1", geometry=QRect(0,0 1920x1080),
> scale=1)
> kwin_wayland_drm: Reading output configuration for 
> KWin::DrmOutput(0x5568aab5b1f0, name="DP-3", geometry=QRect(0,0 3840x2160),
> scale=1)
> kwin_wayland_drm: Received change event for monitored drm device
> "/dev/dri/card0"
> kwin_wayland_drm: Reading output configuration for 
> KWin::DrmOutput(0x5568aab5afd0, name="eDP-1", geometry=QRect(0,720
> 1920x1080), scale=1)

So that sort of confirms my thoughts.

For whatever reason the Connector for your external screen disappears.
The fact that is confirmed in the drm_info output is troubling, kwin should not have any impact on it.
So the bug might lower the stack.

I can add some debug, since you are using the beta.
Once the above merge request lands and I backport it to Kwin 5.23 branch and you have updated packages, we will be able to know a little more.
But in the meantime I can't see anything to ask further, unless you can compile from source the branch.

Btw what is your GPU ?

I'm using a Dell XPX 13 9305 with an Intel Tigerlake CPU and integrated Iris Xe graphics.


-- inxi -G
Device-1: Intel TigerLake-LP GT2 [Iris Xe Graphics] driver: i915 v: kernel
Device-2: Microdia Integrated_Webcam_HD type: USB driver: uvcvideo
Display: wayland server: X.Org 1.21.1.2 driver: loaded: intel unloaded: modesetting resolution: 1920x1080~60Hz
OpenGL: renderer: Mesa Intel Xe Graphics (TGL GT2) v: 4.6 Mesa 21.2.3

*** Bug 434683 has been marked as a duplicate of this bug. ***

Git commit 6d518e8ffe527d1e62d2c1d9949a30fc52429c35 by Méven Car, on behalf of Méven Car.
Committed on 20/10/2021 at 15:33.
Pushed by meven into branch 'master'.

DRM Backend: Add some log trace for DrmConnector

M  +2    -0    src/plugins/platforms/drm/drm_gpu.cpp
M  +25   -1    src/plugins/platforms/drm/drm_object_connector.cpp
M  +4    -0    src/plugins/platforms/drm/drm_object_connector.h

https://invent.kde.org/plasma/kwin/commit/6d518e8ffe527d1e62d2c1d9949a30fc52429c35

Dear Bug Submitter,

This bug has been in NEEDSINFO status with no change for at least
15 days. Please provide the requested information as soon as
possible and set the bug status as REPORTED. Due to regular bug
tracker maintenance, if the bug is still in NEEDSINFO status with
no change in 30 days the bug will be closed as RESOLVED > WORKSFORME
due to lack of needed information.

For more information about our bug triaging procedures please read the
wiki located here:
https://community.kde.org/Guidelines_and_HOWTOs/Bug_triaging

If you have already provided the requested information, please
mark the bug as REPORTED so that the KDE team knows that the bug is
ready to be confirmed.

Thank you for helping us make KDE software even better for everyone!

(In reply to Méven Car from comment #18)
> Git commit 6d518e8ffe527d1e62d2c1d9949a30fc52429c35 by Méven Car, on behalf
> of Méven Car.
> Committed on 20/10/2021 at 15:33.
> Pushed by meven into branch 'master'.
> 
> DRM Backend: Add some log trace for DrmConnector
> 
> M  +2    -0    src/plugins/platforms/drm/drm_gpu.cpp
> M  +25   -1    src/plugins/platforms/drm/drm_object_connector.cpp
> M  +4    -0    src/plugins/platforms/drm/drm_object_connector.h
> 
> https://invent.kde.org/plasma/kwin/commit/
> 6d518e8ffe527d1e62d2c1d9949a30fc52429c35

Have these changes landed?

I've just re-enabled the Arch kde-unstable repo and there weren't any updates, perhaps they're already in the main Arch repo.

Anyway, output from grep kwin_wayland_drm ~/.local/share/sddm/wayland-session.log for my current setup is below.

I've also discovered if I plug a USB-A hub into the same USB-C dongle while it's being used for video, it kills the video output similarly to unplugging and replugging the dongle. A full reboot is required to recover video after this has happened. I've included the additional output of grep kwin_wayland_drm ~/.local/share/sddm/wayland-session.log following plugging the hub in.

It's  worth noting that this hub is usually powered, but I don't have the power adaptor with me right now, so this may not occur when powered.

Happy to do any further testing.

---- New session, plugging in USB-C dongle / monitor for first time
grep kwin_wayland_drm ~/.local/share/sddm/wayland-session.log
kwin_wayland_drm: drmModeAddFB2WithModifiers is supported on GPU "/dev/dri/card0"
kwin_wayland_drm: Using Atomic Mode Setting on gpu "/dev/dri/card0"
kwin_wayland_drm: Number of planes on GPU "/dev/dri/card0" : 32
kwin_wayland_drm: Crtc 98 has properties "MODE_ID"=363, "ACTIVE"=1, "VRR_ENABLED"=0, "GAMMA_LUT"=362
kwin_wayland_drm: Crtc 167 has properties "MODE_ID"=0, "ACTIVE"=0, "VRR_ENABLED"=0, "GAMMA_LUT"=0
kwin_wayland_drm: Crtc 236 has properties "MODE_ID"=0, "ACTIVE"=0, "VRR_ENABLED"=0, "GAMMA_LUT"=0
kwin_wayland_drm: Crtc 305 has properties "MODE_ID"=0, "ACTIVE"=0, "VRR_ENABLED"=0, "GAMMA_LUT"=0
kwin_wayland_drm: EGL buffer configs count: 100
kwin_wayland_drm: Connector 308 has properties "CRTC_ID"=98, "non-desktop"=0, "DPMS"=0, "EDID"=310, "overscan"not found, "vrr_capable"=0, "underscan" not found, "underscan vborder" not found, "underscan hborder" not found, "Broadcast RGB"="Automatic"
kwin_wayland_drm: New output on GPU "/dev/dri/card0": "eDP-1-unknown"
kwin_wayland_drm: Reading output configuration for  KWin::DrmOutput(0x55c21e83ebf0, name="eDP-1", geometry=QRect(0,0 1920x1080), scale=1)
kwin_wayland_drm: Received change event for monitored drm device "/dev/dri/card0"
kwin_wayland_drm: Connector 347 has properties "CRTC_ID"=0, "non-desktop"=0, "DPMS"=3, "EDID"=362, "overscan" not found, "vrr_capable"=0, "underscan" not found, "underscan vborder" not found, "underscan hborder" not found, "Broadcast RGB"="Automatic"
kwin_wayland_drm: New output on GPU "/dev/dri/card0": "DELL S2721QS/5ML3M43"
kwin_wayland_drm: Reading output configuration for  KWin::DrmOutput(0x55c21e83ebf0, name="eDP-1", geometry=QRect(0,0 1920x1080), scale=1)
kwin_wayland_drm: Reading output configuration for  KWin::DrmOutput(0x55c21f19f530, name="DP-3", geometry=QRect(0,0 3840x2160), scale=1)

--- External display not working after USB-A hub plugged into 
kwin_wayland_drm: Received change event for monitored drm device "/dev/dri/card0"
kwin_wayland_drm: Reading output configuration for  KWin::DrmOutput(0x55c21e83ebf0, name="eDP-1", geometry=QRect(0,648 1920x1080), scale=1)

Dear Bug Submitter,

This bug has been in NEEDSINFO status with no change for at least
15 days. Please provide the requested information as soon as
possible and set the bug status as REPORTED. Due to regular bug
tracker maintenance, if the bug is still in NEEDSINFO status with
no change in 30 days the bug will be closed as RESOLVED > WORKSFORME
due to lack of needed information.

For more information about our bug triaging procedures please read the
wiki located here:
https://community.kde.org/Guidelines_and_HOWTOs/Bug_triaging

If you have already provided the requested information, please
mark the bug as REPORTED so that the KDE team knows that the bug is
ready to be confirmed.

Thank you for helping us make KDE software even better for everyone!

This seems to be largely resolved with the update to KDE 5.24.1, Frameworks 5.91.0 and QT 5.15.2.

Plugging and replugging the external monitor works correctly. The monitor is properly detected when plugged in, no matter if it's the first time after a reboot or if it's already been unplugged and replugged.

There are problems with KDE/Wayland not respecting the primary monitor flag, but that's a separate issue.

Oh, that's good!

(In reply to Tim from comment #22)
> This seems to be largely resolved with the update to KDE 5.24.1, Frameworks
> 5.91.0 and QT 5.15.2.
> 
> Plugging and replugging the external monitor works correctly. The monitor is
> properly detected when plugged in, no matter if it's the first time after a
> reboot or if it's already been unplugged and replugged.
> 
> There are problems with KDE/Wayland not respecting the primary monitor flag,
> but that's a separate issue.

I am happily surprised.

Did you also upgrade kernel and drivers along the way ?

> Did you also upgrade kernel and drivers along the way ?

Yes. I'm running Garuda Linux, which is pretty close to Arch so the kernel, etc has been upgraded along the way. It's entirely possible an update has fixed the issue at the kernel or driver level.