Display Issues Intel/Nvidia Tiger Lake

Support & Help Requests Hardware
#1

Hi,

I'm not sure where to start with this one but here's what I have:

Ubuntu Mate 22.04.1
Dell XPS17 with Nvidia as follows:

   description: 3D controller
   product: GA107M [GeForce RTX 3050 Mobile]
   vendor: NVIDIA Corporation
   physical id: 0
   bus info: pci@0000:01:00.0
   logical name: /dev/fb0
   version: a1
   width: 64 bits
   clock: 33MHz
   capabilities: pm msi pciexpress bus_master cap_list rom fb
   configuration: depth=32 driver=nvidia latency=0 mode=3840x2400 visual=truecolor xres=3840 yres=2400
   resources: iomemory:600-5ff iomemory:610-60f irq:204 memory:a9000000-a9ffffff memory:6000000000-60ffffffff memory:6100000000-6101ffffff ioport:3000(size=128)

*-display
description: VGA compatible controller
product: TigerLake-H GT1 [UHD Graphics]
vendor: Intel Corporation
physical id: 2
bus info: pci@0000:00:02.0
logical name: /dev/fb0
version: 01
width: 64 bits
clock: 33MHz
capabilities: pciexpress msi pm vga_controller bus_master cap_list rom fb
configuration: depth=32 driver=i915 latency=0 resolution=3840,2400
resources: iomemory:610-60f iomemory:400-3ff irq:187 memory:618c000000-618cffffff memory:4000000000-400fffffff ioport:4000(size=64) memory:c0000-dffff memory:4010000000-4016ffffff memory:4020000000-40ffffffff

Normally I run at UHD 3840x 2400, however today I inadvertently connected to and additional pair of monitors via USB, and now my primary display has artifacts I can't get rid of, such as plank in the middle of the screen. It's as if there is an HD display within the UHD display in the top left corner.

Has anyone else seen this behaviour?

Link to display image: Screenshot-at-2022-11-15-10-07-53 — ImgBB

Regards
Ian

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#2

Wow, that is really, really weird. I've never seen anything quite like it. I have a hunch about what's wrong, though.

First, can you go to the Main Menu (it seems to be at the bottom left on your setup), search for a tool called "Displays", and open it? The Displays tool should display a window containing information about each and every monitor you have attached to the computer. Please take a screenshot of the Displays window (but not your whole desktop again -- that is unnecessary). Post the screenshot in a post here.

I'm going to go out on a limb here with my hunch. I see that your laptop contains both Nvidia and Intel graphics. I see an applet in your panel that shows the Intel logo -- I'm guessing that's nvidia-optimus, the application for switching between the high-efficiency Intel integrated graphics and the high-powered Nvidia graphics. If this part of my hunch is true, then supposedly you're using the Intel graphics right now.

I suspect that the Nvidia graphics might not be disabled entirely, and one of these phantom displays is produced by the Intel graphics while the other is produced by the Nvidia. The Linux drivers for Nvidia graphics, proprietary or open-source, have always been buggy, and this looks like a pretty typical bug, in the sense that usually Nvidia driver bugs are very noticeable and weird.

Yes, it's weird that the two outputs are of different sizes. And it's weird that this only started happening when you plugged in (two?) new monitors. But I have a theory that the Nvidia and Intel graphics have both been running all along, but the screen resolutions in use on both graphics chips have up until now been identical, so you would never have known.

My first theory is that the two monitors you just added were different resolutions from your primary monitor (which I assume is your built-in laptop monitor?). According to the spec sheet for your XPS17, the monitor resolution is supposedly 1920x1200, though in this day and age of HiDPI (double-pixel-density) monitors, that figure could theoretically be double in reality, which would match the 3840x2400 that you said above. Notice how I mentioned the double-density monitor. It could be that one of the monitors you attached is only single-density and truly 1920x1200 (instead of 3840x2400), and this confused the Nvidia drivers into drawing stuff at single-density even on your double-density primary monitor.

Scratch all that stuff that I struck out (above). I looked into Tiger Lake and realized that the integrated graphics is only designed to drive, at most, two 4K monitors. I'm guessing that the Intel chip draws to two of the monitors (including your primary monitor), and the more powerful Nvidia chip handles the rest -- but steps on the Intel chip's toes since the Nvidia drivers aren't designed for this kind of operation.

I have no experience with Nvidia graphics myself (I own no Nvidia graphics cards or chips and am proud of that fact). Nevertheless, I've heard that if you click the Intel logo icon in the notification area below, it will pop up a dialog that lets you switch between Nvidia and Intel graphics. See if there is an option to disable the Nvidia graphics outright (a check button under the "Nvidia graphics" tab, perhaps?). See if the problem then goes away. Then, try the opposite: Re-enable the Nvidia graphics, and disable Intel.

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#3

Hi Gordon,

Thanks so much for your very comprehensive response, which made me a little ashamed of my inadequate post. Still, lesson learned.

I connected the displays again here's the displays applet showing those monitors. Screenshot-at-2022-12-07-11-48-27 — ImgBB

However there is a wrinkle. The monitors are attached via USB and DisplayLink using the driver for Ubuntu 20.04/22.04 from their site.

About a week after my post I did uninstall the Dell DisplayLink USB driver which was giving me the trouble, but yesterday reinstalled it, and I have confirmed that the version is the same as previously, 5.4.1 released in August 2022. The issue is still present, and its expression appears to be related to the utility Plank as I don't see issues when that is disabled. However I doubt that is the root cause.

Thanks for your assistance.
Ian

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#4

Well, I would say that you're probably right, in that Plank is getting tripped up by your multi-monitor display and nothing else. But in your original screenshot, the desktop background is drawn twice: Once at full scale (covering the whole screen) and once at close to half-scale (covering only the top-left quadrant of the monitor). This would imply that something other than Plank is also confused.

That said, I've run out of ideas for now. And, if you really are using special drivers for these USB-connected displays, you should probably ask on the DisplayLink forums. I'd suggest asking Dell, but I couldn't find any Dell-specific drivers for Linux.

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