Public bug reported:
After upgrading Kubuntu 26.04 -> 26.10, a Thunderbolt 3 monitor (Dell U4021QW,
connected directly to the laptop's USB4 port) stays dark after cold boot or
reboot. It only comes up after unplugging and re-plugging the cable.
Hardware: AMD APU (amdgpu DCN 3.5), USB4 controller 0000:c5:00.6.
Regression:
- 7.0.0-38-generic: works (login screen appears on the monitor)
- 7.3.0-9-generic: broken
Both kernels use the same dracut-generated initramfs, which contains
thunderbolt.ko but not amdgpu, so amdgpu loads ~1.5 s after thunderbolt.
7.0.0-38 (works):
[15.239677] thunderbolt 0000:c5:00.6: 0:6 <-> 2:10 (DP): not active, deferring
until display driver loads
[19.650840] thunderbolt 0000:c5:00.6: 0: failed to allocate DP resource for
port 7
7.3.0-9 (broken):
[14.797480] thunderbolt 0000:c5:00.6: 0:6 <-> 2:10 (DP): not active, tearing
down
[16.066 ] amdgpu 0000:c3:00.0: initializing kernel modesetting ...
[16.268714] thunderbolt 0000:c5:00.6: 0: failed to allocate DP resource for
port 7
-> DP tunnel is never re-established until the cable is re-plugged.
So 7.3 tears down the firmware-created DP tunnel instead of deferring until
the display driver loads, as 7.0 does.
Workaround: load amdgpu from the initramfs
(/etc/dracut.conf.d/10-amdgpu.conf: add_drivers+=" amdgpu "). With amdgpu
initialized at ~3 s the tunnel is kept and the monitor works on 7.3.
Note: the logs attached by apport were collected with this workaround active.
ProblemType: Bug
DistroRelease: Ubuntu 26.10
Package: linux-image-7.3.0-9-generic 7.3.0-9.9
ProcVersionSignature: Ubuntu 7.3.0-9.9-generic 7.3.0-rc6
Uname: Linux 7.3.0-9-generic x86_64
ApportVersion: 2.36.0-0ubuntu1
Architecture: amd64
AudioDevicesInUse:
USER PID ACCESS COMMAND
/dev/snd/controlC1: madlp 2704 F.... pipewire
madlp 2706 F.... wireplumber
/dev/snd/controlC0: madlp 2706 F.... wireplumber
/dev/snd/seq: madlp 2704 F.... pipewire
CasperMD5CheckResult: unknown
CurrentDesktop: KDE
Date: Fri Oct 16 15:47:12 2026
InstallationDate: Installed on 2026-08-21 (56 days ago)
InstallationMedia: Kubuntu 26.04 "Resolute Raccoon" - Release amd64 (20260423)
MachineType: Dell Inc. Dell Pro 7 14 2-in-1 P704265
ProcFB: 0 amdgpudrmfb
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-7.3.0-9-generic
root=UUID=2eb134fa-3034-4f41-aef8-25cf6622d5cf ro quiet
cryptdevice=UUID=07d1fd83-c73a-45ac-b46f-6ed2521c1f58:luks-07d1fd83-c73a-45ac-b46f-6ed2521c1f58
root=/dev/mapper/luks-07d1fd83-c73a-45ac-b46f-6ed2521c1f58 splash
PulseList: Error: command ['pacmd', 'list'] failed with exit code 1: No
PulseAudio daemon running, or not running as session daemon.
SourcePackage: linux
UpgradeStatus: Upgraded to stonking on 2026-10-16 (0 days ago)
dmi.bios.date: 09/30/2026
dmi.bios.release: 2.1
dmi.bios.vendor: Dell Inc.
dmi.bios.version: 2.1.2
dmi.board.name: 052YF9
dmi.board.vendor: Dell Inc.
dmi.board.version: A00
dmi.chassis.type: 31
dmi.chassis.vendor: Dell Inc.
dmi.ec.firmware.release: 1.5
dmi.modalias:
dmi:bvnDellInc.:bvr2.1.2:bd09/30/2026:br2.1:efr1.5:svnDellInc.:pnDellPro7142-in-1P704265:pvr:rvnDellInc.:rn052YF9:rvrA00:cvnDellInc.:ct31:cvr:sku0E24:pfaDellProLaptops:
dmi.product.family: Dell Pro Laptops
dmi.product.name: Dell Pro 7 14 2-in-1 P704265
dmi.product.sku: 0E24
dmi.sys.vendor: Dell Inc.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Tags: amd64 apport-bug stonking third-party-packages wayland-session
--
You received this bug notification because you are a member of Ubuntu
Bugs, which is subscribed to Ubuntu.
https://bugs.launchpad.net/bugs/2171090
Title:
Thunderbolt DP tunnel torn down before amdgpu loads; TB3 monitor stays
dark after boot (regression 7.0 -> 7.3)
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2171090/+subscriptions
--
ubuntu-bugs mailing list
[email protected]
https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
