Ubuntu 20.04 portrait mode issues

I have an RTX 2070 Super video card running on Ubuntu 20.04 whose USB-C output is connected to my UD-ULTCDL triple monitor dock.

This is exact setup works well in Windows 10 and drives my three monitors properly with the main large 43" one in landscape mode and a 24" on each side in portrait mode.

In Ubuntu not so much with 440.100 NVidia drivers (Ubuntu supplied) and the DisplayLink driver 5.3.1.34 from DisplayLink.

The centre screen is fine but the side ones have issues. First problem is there’s keyboard input lag within the satellite monitor windows when I make one of them active by clicking on them but the far bigger problem is the way the mouse moves.

After moving the mouse pointer into either screen, it jumps past part of the screen making that portion unusable. It’s only a small amount for the right hand one screen but a full 20% of the left one which is not workable. A phantom pointer also remains in each of the side screens when the mouse is returned back into the centre screen.

This behaviour doesn’t occur when the side screens are in landscape mode (at least no phantom or unusable screen) but changing their orientation to side step the issue I’m having is not really a good option as I’m tight for space given the monitor sizes plus I intentionally bought a large centre one whose height matched the width of the side ones so the mouse would transition between the screens well.

I noticed there’s a DisplayLink forum posting about a patched XServer which I tried but that didn’t correct the problem so I ended up reverting that and am not sure what to try next as I’m quite new to Ubuntu and would really like to get this working.

I see from other forum posts here that DisplayLink is not officially supported by Plugable but would appreciate any ideas that anyone in the community might have.

I also posted this to the same DisplayLink forum here with screenshots of how things are configured.

Hello Dave,

Thank you for contacting Plugable support! Sorry to hear about this issue.

Unfortunately, as you already know, we don’t officially support Linux with our DisplayLink based docking stations. As such we’re not testing these features ourselves, my apologies!

However, from reading about your issue, I might recommend to try the NVIDIA provided drivers vs the included drivers from Ubuntu and see if there may be any difference in behavior.

Or, after speaking with our resident Linux expert, he suggested that DisplayLink in Ubuntu 18.04 had better support if you are able to revert to the previous distro, though I understand that may not be possible or worth the effort (and it may not help).

Please don’t hesitate to let us know of other questions.

Thanks again for contacting Plugable support and best wishes!

Joshua Henry

Senior Engineer | Product Owner
Plugable Technologies

Thanks Joshua,

I tried upgrading to the latest 450.66 NVidia drivers which didn’t fix things and neither did the rather drastic step of starting over with 18.04.

For the 18.04 experiment I initially used the DL 5.2.0 drivers which their site implies one has to use for legacy Ubuntu but compilation didn’t work, I think due to incompatibility with the latest 18.04 linux kernel.

After checking the release notes for the newer drivers, I used the latest DL 5.3.1 one which did compile and install properly but I observed the same behaviour as I saw in 20.04 so I reinstalled 20.04.

I then tried disabling the NVidia card entirely through the NVidia X Server applet by selecting ‘Intel only’ within their Prime profiles. That seemed to make the problems I noticed all go away as keyboard input in side portrait mode monitor terminals no longer had any lag and inter screen mouse transitions were smooth with no ghosts left behind.

Disabling the NVidia graphics card isn’t an option as I need it for Machine Learning programming initiatives so I reverted that.

I did however stumble upon one semi workaround by opening up the display settings after every reboot and either A) shifting the relative position of the main landscape central window up or down a small amount or B) flipping both the sides portrait modes from L to R (or vice versa) and then back again.

That gets rid of the mouse skipping parts of the screen and leaving ghosts but unfortunately doesn’t correct the keyboard lag. I think this lag is due to the graphics driver not processing redraw events as it will just sit there not looking like it saw the keystrokes until the mouse is moved by a decent amount.

So I’m able to get by for now by doing keyboard-centric activities in the central window and reserving the side ones for things like documents I just need to refer to rather than actively edit.

I have ordered a DisplayPort -> HDMI adapter so I can hook up the side ones directly to the NVidia card outputs (there’s just 1 HDMI with the rest DP) to see if bypassing the dock helps in some way.

Once I know the answer to that I’ll likely submit a bug report to NVidia as portrait mode issues with their driver seem to be happening for others in other non DisplayLink contexts across linux distros. Hopefully they’ll take notice and fix it.

Thanks for taking the time to provide some guidance and hopefully me documenting what steps I took and my conclusions will be of help to someone else.

Dave

No problem, happy to help how I can. Though I apologize that our Linux support is so limited.

I also must apologize for recommending the NVIDIA drivers in my previous reply, I did some further digging and did find that DisplayLink won’t support them, or at least at this time:

https://support.displaylink.com/knowledgebase/articles/641668-known-issues-with-displaylink-ubuntu-support

“Closed source AMD/NVIDIA drivers are incompatible with DisplayLink driver. Please use open-source AMD/NVIDIA drivers instead.”

Reporting these bugs you’ve encountered to NVIDIA/Ubuntu/DisplayLink is likely the best option moving forward.

Best,
Josh

Yeah, I think ultimately the nVidia drivers and their current idiosyncrasies are something that I’ll need to live with for the time being as Nouveau apparently doesn’t support CUDA.

I bought my mid level nVidia GPU for CUDA programming (school) and to also leverage it for machine learning (school too) so going down a road without proper low level proprietary access to the hardware seems problematic.

My HDMI -> DP adapter arrived the other day and seemed to iron out the lag and mouse behaviour issues on one of the screens driven by the nVidia card (vs having it plugged into the dock) which definitely points to a DisplayLink / nVidia driver incompatibility in certain circumstances.

Think I’ll order another so I have the option to bypass the dock for both the side monitors for times that I anticipate will be long personal study / coding sessions (vs my day job plugged into the dock from my work Win 10 laptop).

On the bright side, USB, audio and my main central monitor all work great via the dock for both Windows 10 and Ubuntu so I’m good overall!

Thanks again for the assistance.

Dave

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