[Bug 2161425] Re: Lenovo Thunderbolt 4 dock intermittently fails or disconnects, causing USB device loss and both Radeon 680M-driven external MST displays to blank

Update: This is not a new 7.0 regression. Retained journals show the same dock-path failures on Ubuntu kernels 6.17.0-22-generic and 6.17.0-23-generic: USB setup/address failures (error -71), Thunderbolt disconnects, and AMDGPU AUX/MST/DPCD link errors. For example, a 6.17.0-22 boot logged 10 USB errors, 28 AUX/MST4 errors, and 183 Thunderbolt disconnect messages; another logged 13 USB errors, 24 AUX/MST errors, and 603 Thunderbolt disconnects. The newer 7.0 series adds recurring dcn31_program_compbuf_size warnings, first observed locally on 7.0.0-15, but 7.0.0-28 still exhibits the underlying failure: the dock can disconnect at runtime, blank both external displays, then re-enumerate. -- You received this bug notification because you are subscribed to linux in Ubuntu. Matching subscriptions: Bgg, Bmail, Nb https://bugs.launchpad.net/bugs/2161425 Title: Lenovo Thunderbolt 4 dock intermittently fails or disconnects, causing USB device loss and both Radeon 680M-driven external MST displays to blank Status in linux package in Ubuntu: New Bug description: # System - Lenovo ThinkPad T14s Gen 3 (`21CRS08P00`) - AMD Rembrandt / Radeon 680M (`1002:1681`) - BIOS `R22ET81W (1.51)`, dated 2026-04-10 - Lenovo ThinkPad Universal Thunderbolt 4 Smart Dock - Ubuntu 26.04 LTS - Kernel `7.0.0-28-generic`, package version `7.0.0-28.28` - `linux-firmware` version `20260319.git217ca6e4.1ubuntu` # Expected result The dock should enumerate reliably on either supported laptop USB-C port. Its USB devices and both external displays should remain connected, without AMDGPU warnings or GNOME atomic-commit failures. # Actual result Observed outcomes include: 1. USB setup fails with `device not accepting address ..., error -71`; no Thunderbolt device or DP MST topology is created. 2. A docked boot shows `failed to allocate DP resource for port 7`, `DMUB notification skipped due to no handler: type=HPD`, and `DM_MST: Differing MST start`, then eventually recovers. 3. After successful enumeration, the entire dock disconnects and re-enumerates at runtime. Both external displays blank, GNOME reports failed atomic commits, and AMDGPU reports DPIA allocation-table and DCN compbuf warnings. # Reproduction / observations 1. Boot Ubuntu with the dock's rear/upstream port and both external displays already connected, or boot undocked and connect the dock after login. 2. Observe either successful enumeration or an early USB `error -71` failure. The result is port/path-sensitive: - Rear/upstream dock port to one laptop USB-C port: failed after the initial USB attempt with `error -71`; no Thunderbolt or display event followed. - Rear/upstream dock port to the other laptop USB-C port: full dock enumeration and both displays worked, after one recoverable AMDGPU `Sending link address failed with -5` message. 3. During a separate successful `7.0.0-28-generic` boot, the dock later disconnected and re-enumerated. Both displays went off and came back. # Relevant kernel messages Runtime disconnect on `7.0.0-28-generic`: ```text DM_MST: stopping TM USB devices below usb 8-1 and usb 9-1 disconnect thunderbolt 0-2: device disconnected gnome-shell: Page flip failed: drmModeAtomicCommit: Invalid argument WARNING in update_dpia_stream_allocation_table [amdgpu] REG_WAIT timeout in dcn31_program_compbuf_size WARNING in dcn31_program_compbuf_size [amdgpu] Lenovo ThinkPad Universal Thunderbolt 4 Smart Dock detected again DM_MST: starting TM; DP14, 4-lane link detected ``` Docked-boot initialization on `7.0.0-28-generic`: ```text thunderbolt 0000:34:00.6: 0: failed to allocate DP resource for port 7 amdgpu: [drm] DMUB notification skipped due to no handler: type=HPD amdgpu: [drm] DM_MST: Differing MST start on aconnector ``` Failed hot-plug through one laptop USB-C port: ```text usb 8-1: Device not responding to setup address. usb 8-1: device not accepting address 2, error -71 ``` # Historical information Retained journals from kernels `6.17.0-22` and `6.17.0-23` already contain USB enumeration failures, Thunderbolt disconnects, and AMDGPU AUX/MST/DPCD failures. The `dcn31_program_compbuf_size` warning is newer locally: it first appears with `7.0.0-15-generic` and recurs through `7.0.0-27-generic`. # Notes The sequence suggests an interaction between USB4/Thunderbolt DP tunnel setup and AMDGPU DPIA/MST initialization, but that is only an inference from log ordering, not a root-cause claim. Please triage with both the Ubuntu kernel and relevant upstream AMDGPU/Thunderbolt components in mind. A one-time oops in `trigger_hpd_mst_set [amdgpu]` occurred only after manually writing an AMDGPU debugfs MST trigger. It was not part of normal operation, so I will report it separately if needed rather than using it as a workaround or conflating it with this issue. # Attachments 1. The Apport report generated with `ubuntu-bug linux`. 2. Full kernel journals for: the runtime-disconnect boot, the docked boot showing DP-resource/MST-ordering messages, the failed hot-plug path, and the successful alternate-port path. 3. `sudo boltctl list --verbose` (if Bolt is installed) and `lspci -nnk`. 4. Do not use the AMDGPU debugfs MST HPD trigger; it caused a separate diagnostic-only oops in this environment. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2161425/+subscriptions