Bug 425744

Summary: displaylink monitor not recognized
Product: [Plasma] kwin Reporter: San <sanette-linux>
Component: wayland-genericAssignee: KWin default assignee <kwin-bugs-null>
Status: RESOLVED FIXED    
Severity: normal CC: xaver.hugl
Priority: NOR Keywords: wayland-only
Version First Reported In: 5.19.4   
Target Milestone: ---   
Platform: Neon   
OS: Linux   
Latest Commit: Version Fixed/Implemented In:
Sentry Crash Report:

Description San 2020-08-24 13:50:35 UTC 
SUMMARY

External monitor on a Displaylink device is not recognized by Plasma-Wayland
(but it does work with Plasma-Xorg)


STEPS TO REPRODUCE
1. install and start the displaylink driver
https://www.displaylink.com/downloads/file?id=1576
2. reboot
3. log-in selecting Plasma-Wayland
4. plug-in an external monitor on the Displaylink device

OBSERVED RESULT

Monitor is not recognized (neither by xrandr nor by Plasma Screen configuration)


EXPECTED RESULT

external monitor should be recognized, as it is with Plasma-Xorg


SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Neon User Edition 5.19
KDE Plasma Version: 5.19.4
KDE Frameworks Version: 5.73.0
Qt Version: 5.14.2

ADDITIONAL INFORMATION

Dell XPS 13 laptop with USB Displaylink extension (including audio, ethernet, and HDMI for external monitors)
Comment 1 Zamundaaa 2021-02-18 11:44:45 UTC 
With 5.21 we have multi-gpu support - as DisplayLink is AFAIK recognized as a GPU it might work now, as long as you have it connected on boot (hotplugging shouldn't be difficult but isn't implemented yet). So please test again :)

Also, what does
ls /dev/dri/
output, with and without the displaylink device being connected?
Comment 2 San 2021-02-18 17:47:11 UTC 
WOW! it works! Thanks!

Now I can set different scalings to monitors with very different resolutions, and move a window from one to the other while the window appears more or less the same on both! (that is, not like twice smaller on one monitor).
I've been waiting for this moment for soooo long ;)

Here is the output of $ ls /dev/dri/
by-path  card0  card1  card2  card3  card4  renderD128

(while monitor is connected). If I disconnect it, I have the same.
Comment 3 Zamundaaa 2021-02-18 18:16:34 UTC 
Cool!

> Here is the output of $ ls /dev/dri/
>by-path  card0  card1  card2  card3  card4  renderD128
>(while monitor is connected). If I disconnect it, I have the same.

That's quite interesting, I don't assume you have 4 GPUs installed, so the driver apparently creates multiple devices... I also assumed that the card device would get dynamically added and removed by the kernel, apparently not so then.

Did you try hot-unplugging? If it doesn't remove the cardX device then it most likely won't crash. Also, does hotplugging work if you don't plug it in at boot?
Comment 4 San 2021-02-23 14:08:25 UTC 
yes, the displaykink driver seems to give me 4 screens:

$ ls /dev/dri/by-path/
pci-0000:00:02.0-card  pci-0000:00:02.0-render  platform-evdi.0-card  platform-evdi.1-card  platform-evdi.2-card  platform-evdi.3-card
Comment 5 Zamundaaa 2021-02-25 07:05:10 UTC 
Thanks! I think them support for DisplayLink should be complete; if there are remaining issues then just open a new bug report