Wayland does not properly recognize Displayport 1.2 MST configuration

Affected version

• Gnome 3.36
• NixOS Unstable (39247f8d04c)
• Mutter 3.36.0
• Wayland

Bug summary

I am using a Dell U2414P display in MST mode, which enables 4K@60Hz on Displayport 1.2 by presenting the display as two independent 1080p displays.

In Gnome 3.34, this worked fine. Since upgrading to 3.36, I encounter the following issues when enabling MST:

• display is horizonally tiled (both login screen and desktop)
• screen runs at 4K@60hz
• left half of Gnome desktop is visible in both halves of the screen
• mouse pointer goes across the screen, but only left half of screen is clickable

Everything works fine when I switch the display to single stream mode, however then it is only driven at 4K@30Hz. Under xorg, all is fine both using MST and SST.

Relevant logs, screenshots, screencasts etc.

Output of modetest (SST mode, 4K@30Hz): 30hz

Output of modetest (MST mode, 4K@60Hz): 60hz

Output of xrandr (xorg, 4K@30Hz): xrandr30hz

Output of xrandr (xorg, 4K@60Hz): xrandr60hz