Wayland + Nvidia + an old MST 4k monitor = half a screen

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Greetings all!

I’m trying to make myself at home on a fresh NixOS installation (25.11) for the first time. I have an RTX 2060 and an old 4k monitor (Sharp PN-K322B). 4k monitors of this vintage had to work around some sort of bandwidth limitation and did so by sending two parallel data streams over Multi-Stream Transport. Somehow the operating system is supposed to understand what’s going on and stitch the two streams into a single logical display.

Unfortunately I’m only getting one stream, and am writing to you using the right half of my monitor. Some additional details:

  • If I instead plug the monitor into my motherboard, I get both halves but they’re recognized as two separate monitors.
  • I’ve tried both open and non-open Nvidia driver packages. (I haven’t tried Nouveau and I’m not sure that would be a solution I would live with.)
  • The connection is DP 1.2.
  • This same hardware configuration previously worked as expected up to about three years ago under Pop!_OS with Gnome and X11. (I’ve been on Windows since then.)

So I think I’m basically experiencing two separate problems:

  1. The graphics card won’t receive both display streams.
  2. I’m unable to combine both streams into a single display.

I’ve looked through a lot of forum discussions about people experiencing similar problems and it looks like satisfactory resolutions are rare. I don’t usually do this, but I asked ChatGPT for advice. I’ve been trying its suggested modifications to my configuration.nix, which has been an interesting learning experience but hasn’t solved either problem so far.

At one point, after switching the monitor to SST mode (which gets me full resolution at 30Hz) and then back to MST, I briefly had two logical displays while plugged into the graphics card, which suggests to me there may be something to something someone said in one of those forum discussions about the displays being enumerated before the connection is fully up and running. But that state didn’t survive a reboot, and I’m not sure how to investigate further.

Something ChatGPT told me was that Wayland is simply not great about working with this MST arrangement, and that I might have to switch to X11. If that’s the case, I’ll probably reinstall Windows and maybe try this again in another couple of years.

Thanks in advance for any advice anyone is able to share!

1 Like
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Which compositor/DE/WM are you using? I imagine this will have to be supported by the specific compositor, doubt this can be handled on the protocol level, so you’ll need to look for explicit support there.

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Oh sorry, I forgot to mention that: I’m using KDE and KWin.

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An update: I fixed this issue by replacing my monitor.