## What happened

Plugging a USB-C→HDMI adapter (Cable Matters) into one of the laptop's Thunderbolt/USB-C ports fails to bring up any display output. The kernel log shows the adapter's DisplayPort Alt Mode negotiation getting corrupted and falling back to USB2-only:

```
usb 3-2: not running at top speed; connect to a high speed hub
usb 3-2: New USB device found ... Manufacturer: Cable Matters Inc. Product: billboard
ucsi_acpi USBC000:00: con1: Firmware bug: duplicate partner altmode SVID 0xff01 at offset 1, ignoring but please contact the BIOS vendor to fix this issue.
ucsi_acpi USBC000:00: con1: VDO mismatch: 0xff01a043 vs 0x00001005
```

After this, the adapter enumerates only as a USB "billboard" device (the fallback identity a Type-C alt-mode adapter reports when alt-mode negotiation fails), and no new DRM connector appears:

```
$ for c in /sys/class/drm/card*-*; do echo "$(basename $c): $(cat $c/status)"; done
card0-DP-1: disconnected
card0-DP-2: connected      # separate monitor on a different port, working fine
card0-DP-3: disconnected
card0-eDP-1: connected
```

`/sys/class/typec/port0/port0-partner/` confirms the port is wedged:
```
usb_mode: [usb2]
port0-partner.0 (SVID ff01, VESA DisplayPort Alt Mode): active=yes  <- claims active but no video lanes routed
```

**The affected USB-C port then stays wedged in this state until a full system reboot.** Unplugging/replugging the adapter, or trying to reset it via sysfs, does not clear it — the bad state appears to live in the embedded/UCSI controller firmware, not just the kernel driver.

## Expected

USB-C→HDMI DisplayPort Alt Mode negotiation should succeed reliably, and if it does glitch once, replugging the adapter (without a full reboot) should be enough to recover it.

## Steps to reproduce

1. On a Dell XPS 16 (Panther Lake, Intel Core Ultra X7 358H / Arc B390 `xe` driver), plug a USB-C→HDMI adapter into one of the Thunderbolt/USB-C ports while another external monitor is already connected via native DisplayPort on a different port.
2. Observe `journalctl -k` for the `ucsi_acpi` firmware-bug / VDO-mismatch messages and the adapter enumerating as `billboard`.
3. No display output reaches the HDMI-connected monitor; `/sys/class/drm/card0-DP-*` for that port stays `disconnected`.
4. Unplug/replug the adapter — port stays wedged (`usb_mode: [usb2]`).
5. Reboot — port works normally again until the bug recurs.

## System details

- Omarchy: 4.0.3-1
- Kernel: 7.1.8-arch1-2-ptl (`Linux omarchy 7.1.8-arch1-2-ptl #1 SMP PREEMPT_DYNAMIC Wed, 12 Aug 2026`)
- Hardware: Dell XPS 16 (DA16260)
- CPU/iGPU: Intel Core Ultra X7 358H, Panther Lake Arc B390, `xe` driver
- Adapter: Cable Matters USB-C→HDMI (idVendor=0bda, idProduct=5452)

## Note

This looks like it may ultimately be an upstream kernel/`ucsi_acpi`/Dell BIOS firmware issue (the kernel's own log points at "contact the BIOS vendor") rather than something Omarchy's userspace config controls, but filing here per Omarchy's own troubleshooting guidance since it's a recurring, reboot-only-fixable regression on a supported Omarchy machine. Happy to help narrow it down further (bisect kernel versions, test with a different adapter/port, etc.) if useful.