LUKS prompt is invisible on tiled 5K displays (Apple Studio Display): Plymouth lights both tile connectors

System details

Dell XPS 14 DA14260, Intel Core Ultra X9 388H (Panther Lake, Arc B390, xe), Apple Studio Display via CalDigit TS4 (Thunderbolt), Omarchy 4.0.6, plymouth 26.134.222-3, kernel 7.1.8-arch1-2-ptl

What's wrong?

With the Studio Display connected through the dock at boot, the Plymouth LUKS prompt never becomes usable. I have to unplug the dock every boot before I can see the prompt and type my passphrase.

Cause: the Studio Display is a tiled panel. The kernel exposes it as two connected connectors:

DP-1: 5120x2880 3840x2160 2560x2880 ...   (full panel)
DP-2: 2560x2880                            (second tile)

DP-1's TILE property is 1:1:2:1:0:0:2560:2880 (2x1 tiles, single-monitor group). Hyprland drives only DP-1 at 5120x2880 and leaves DP-2 off, which works fine.

Plymouth's DRM renderer doesn't group tiles. It lights every connected connector. From a plymouth.debug log with the dock connected:

00:00:05.630 drm/plugin.c:587: Adding connector with id 521 to 5120x2880 head      # DP-1, full 5K
00:00:06.167 drm/plugin.c:1519: Using controller 389 for connector 534             # DP-2 gets its own CRTC
00:00:06.167 drm/plugin.c:587: Adding connector with id 534 to 2560x2880 head      # second tile as a separate head
00:00:06.201 drm/plugin.c:712: Setting scan out buffer of 2560x2880 head to our buffer

Driving the full 5K mode on DP-1 and the second tile on DP-2 at the same time leaves no usable prompt on any screen. A passphrase typed blind was rejected (got password answer at 54.0s, then a new password request). After I unplugged the dock at 57.4s, Plymouth dropped to one head and the passphrase worked.

Workaround: disabling the second tile's connector on the kernel command line fixes it. The prompt then shows on both the laptop and the Studio Display:

# /etc/limine-entry-tool.d/studio-display-tile.conf
KERNEL_CMDLINE[default]+=" video=DP-2:d"

The connector name depends on the port and machine, so a hardcoded value isn't a general fix. Options I can think of:

• Omarchy detects tiled monitors (a connector whose TILE blob has a non-zero tile location) and disables those connectors for Plymouth only. For example, it could add video=<connector>:d at install time, or ship a udev rule that runs before plymouthd.
• Report it upstream to Plymouth so the DRM renderer skips non-origin tiles, or merges them into one head, when another connector in the same tile group already drives the full mode.

Note on the setup: I've only tested through a CalDigit TS4, not with the Studio Display connected directly to the laptop. I think the dock isn't the cause: the second connector comes from the display's own TILE data, and disabling DP-2 alone fixed it with the dock still connected. Both tiles do share the dock's Thunderbolt link, though, so I can't rule out the dock making it worse.

Possibly related: the off-center/cut-off prompt when a display appears late, which is already fixed by #11641. With the workaround above on 4.0.6, I still see that symptom, and #11641 should address it once released. This issue is specifically about the second tile connector.

Steps to reproduce:

1. Connect a tiled 5K display (Apple Studio Display; likely also LG UltraFine 5K) over Thunderbolt (tested through a CalDigit TS4).
2. Boot with full-disk encryption.
3. The LUKS prompt is not usable until the display is disconnected.