Bug#1111558: linux-image-amd64: USB-C DisplayPort Alt Mode regression - external dock monitors not detected after stable release
Package: linux-image-amd64
Version: 6.12.41-1
Severity: critical
Tags: a11y
Justification: breaks the whole system
X-Debbugs-Cc: debian-amd64@lists.debian.org, antti@jalomaki.com
User: debian-amd64@lists.debian.org
Usertags: amd64
After upgrading from Debian 13 testing to stable (released version 13.0),
external monitors connected via USB-C docks no longer work.
Hardware:
- ThinkPad E15 AMD (Ryzen with Radeon Vega Graphics)
- AMD Renoir [Radeon Vega Series] (PCI ID: 05:00.0)
- Tested with two docks:
* HP G4 USB-C Dock (1xHDMI Samsung 4K)
* Thinkpad Thunderbolt 4 Workstation Dock (type 40B0) (2xDP ThinkVision 2K)
- These both docks still work flawlessly with identical Debian 13 KDE Plasma, with Thinkpad X1 Yoga Gen5, i7-10610U & Intel UHD Graphics
Symptoms:
- External monitors not detected (xrandr shows only eDP-1)
- USB-C dock detected but in "Billboard" mode (USB fallback, no DisplayPort)
- No /sys/class/typec/ entries despite typec_ucsi module loaded
- Same docks work with Intel-based ThinkPad X1 Yoga Gen5
What worked:
- External monitors worked correctly during Debian 13 testing phase
- Stopped working after Debian 13 stable release (around one week ago)
What was tried:
- Fresh reinstall of Debian 13 stable - issue persists
- Kernel parameters: usb_storage.quirks, typec.try_role_src=1, amdgpu.dc=0
- Firmware updates (BIOS, dock firmware)
- Both Wayland and X11 sessions
Expected: External monitors should be detected and usable via USB-C docks
Actual: Docks fall back to Billboard mode, no display output
This appears to be a regression between testing and stable release.
-- System Information:
Debian Release: 13.0
APT prefers stable-updates
APT policy: (500, 'stable-updates'), (500, 'stable-security'), (500, 'stable')
Architecture: amd64 (x86_64)
Kernel: Linux 6.12.41+deb13-amd64 (SMP w/8 CPU threads; PREEMPT)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled
Versions of packages linux-image-amd64 depends on:
ii linux-image-6.12.41+deb13-amd64 6.12.41-1
linux-image-amd64 recommends no packages.
linux-image-amd64 suggests no packages.
-- no debconf information
Reply to: