Public bug reported:

On Ubuntu 24.04 LST with the stock kernel 6.8.0‑59‑generic, when I
connect two external monitors—one via the laptop’s HDMI port and one via
a Lenovo Thunderbolt dock (DP‑ALT pass‑through)—the HDMI‑connected
monitor is no longer detected (it vanishes from xrandr). If I unplug the
dock, the HDMI monitor returns; even if I boot an older kernel
(6.8.0‑57), both monitors don't work simultaneously.

Expected behavior:
Both external monitors (HDMI‑2 and DP‑6), and the internal eDP‑1, should be 
detected and driven simultaneously.

Actual behavior:
Only eDP‑1 (internal) + DP‑6 (dock) are active; HDMI‑2 is not even listed by 
xrandr.

Hardware:

    Laptop: Lenovo T480s

    Dock: Lenovo Thunderbolt Dock (DP‑ALT, no MST)

    Monitors:

        eDP‑1 (internal) 1920×1080

        HDMI‑2 2560×1440 (direct)

        DP‑6 2560×1440 (via dock)

Steps to reproduce:

    Boot into kernel 6.8.0‑59‑generic.

    Log in to Ubuntu on Wayland or Xorg.

    Connect one monitor to the laptop HDMI port.

    Connect a second monitor to the Thunderbolt dock.

    Run: xrandr

Observe that DP-6 is “connected” but HDMI-2 is missing.

ProblemType: Bug
DistroRelease: Ubuntu 24.04
Package: linux-image-6.8.0-59-generic 6.8.0-59.61
ProcVersionSignature: Ubuntu 6.8.0-59.61-generic 6.8.12
Uname: Linux 6.8.0-59-generic x86_64
ApportVersion: 2.28.1-0ubuntu3.5
Architecture: amd64
AudioDevicesInUse:
 USER        PID ACCESS COMMAND
 /dev/snd/seq:        lorenzo    3504 F.... pipewire
 /dev/snd/controlC0:  lorenzo    3508 F.... wireplumber
 /dev/snd/controlC1:  lorenzo    3508 F.... wireplumber
CasperMD5CheckResult: unknown
CurrentDesktop: ubuntu:GNOME
Date: Fri May  2 21:31:15 2025
InstallationDate: Installed on 2023-04-26 (737 days ago)
InstallationMedia: Ubuntu 23.04 "Lunar Lobster" - Release amd64 (20230418)
MachineType: LENOVO 20L8S8K30L
ProcFB: 0 i915drmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-6.8.0-59-generic 
root=UUID=a4811af7-d5ef-4599-ba77-d723e024b360 ro quiet splash vt.handoff=7
RelatedPackageVersions:
 linux-restricted-modules-6.8.0-59-generic N/A
 linux-backports-modules-6.8.0-59-generic  N/A
 linux-firmware                            20240318.git3b128b60-0ubuntu2.11
SourcePackage: linux
UpgradeStatus: Upgraded to noble on 2024-08-27 (248 days ago)
dmi.bios.date: 03/17/2025
dmi.bios.release: 1.60
dmi.bios.vendor: LENOVO
dmi.bios.version: N22ET83W (1.60 )
dmi.board.asset.tag: Not Available
dmi.board.name: 20L8S8K30L
dmi.board.vendor: LENOVO
dmi.board.version: SDK0J40697 WIN
dmi.chassis.asset.tag: No Asset Information
dmi.chassis.type: 10
dmi.chassis.vendor: LENOVO
dmi.chassis.version: None
dmi.ec.firmware.release: 1.23
dmi.modalias: 
dmi:bvnLENOVO:bvrN22ET83W(1.60):bd03/17/2025:br1.60:efr1.23:svnLENOVO:pn20L8S8K30L:pvrThinkPadT480s:rvnLENOVO:rn20L8S8K30L:rvrSDK0J40697WIN:cvnLENOVO:ct10:cvrNone:skuLENOVO_MT_20L8_BU_Think_FM_ThinkPadT480s:
dmi.product.family: ThinkPad T480s
dmi.product.name: 20L8S8K30L
dmi.product.sku: LENOVO_MT_20L8_BU_Think_FM_ThinkPad T480s
dmi.product.version: ThinkPad T480s
dmi.sys.vendor: LENOVO

** Affects: linux (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: amd64 apport-bug noble wayland-session

** Attachment added: "version.log"
   
https://bugs.launchpad.net/bugs/2109863/+attachment/5875457/+files/version.log

-- 
You received this bug notification because you are a member of Kernel
Packages, which is subscribed to linux in Ubuntu.
https://bugs.launchpad.net/bugs/2109863

Title:
  Regression: HDMI output not detected when Thunderbolt (DP‑ALT) dock is
  connected on kernel 6.8.0‑59

Status in linux package in Ubuntu:
  New

Bug description:
  On Ubuntu 24.04 LST with the stock kernel 6.8.0‑59‑generic, when I
  connect two external monitors—one via the laptop’s HDMI port and one
  via a Lenovo Thunderbolt dock (DP‑ALT pass‑through)—the HDMI‑connected
  monitor is no longer detected (it vanishes from xrandr). If I unplug
  the dock, the HDMI monitor returns; even if I boot an older kernel
  (6.8.0‑57), both monitors don't work simultaneously.

  Expected behavior:
  Both external monitors (HDMI‑2 and DP‑6), and the internal eDP‑1, should be 
detected and driven simultaneously.

  Actual behavior:
  Only eDP‑1 (internal) + DP‑6 (dock) are active; HDMI‑2 is not even listed by 
xrandr.

  Hardware:

      Laptop: Lenovo T480s

      Dock: Lenovo Thunderbolt Dock (DP‑ALT, no MST)

      Monitors:

          eDP‑1 (internal) 1920×1080

          HDMI‑2 2560×1440 (direct)

          DP‑6 2560×1440 (via dock)

  Steps to reproduce:

      Boot into kernel 6.8.0‑59‑generic.

      Log in to Ubuntu on Wayland or Xorg.

      Connect one monitor to the laptop HDMI port.

      Connect a second monitor to the Thunderbolt dock.

      Run: xrandr

  Observe that DP-6 is “connected” but HDMI-2 is missing.

  ProblemType: Bug
  DistroRelease: Ubuntu 24.04
  Package: linux-image-6.8.0-59-generic 6.8.0-59.61
  ProcVersionSignature: Ubuntu 6.8.0-59.61-generic 6.8.12
  Uname: Linux 6.8.0-59-generic x86_64
  ApportVersion: 2.28.1-0ubuntu3.5
  Architecture: amd64
  AudioDevicesInUse:
   USER        PID ACCESS COMMAND
   /dev/snd/seq:        lorenzo    3504 F.... pipewire
   /dev/snd/controlC0:  lorenzo    3508 F.... wireplumber
   /dev/snd/controlC1:  lorenzo    3508 F.... wireplumber
  CasperMD5CheckResult: unknown
  CurrentDesktop: ubuntu:GNOME
  Date: Fri May  2 21:31:15 2025
  InstallationDate: Installed on 2023-04-26 (737 days ago)
  InstallationMedia: Ubuntu 23.04 "Lunar Lobster" - Release amd64 (20230418)
  MachineType: LENOVO 20L8S8K30L
  ProcFB: 0 i915drmfb
  ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-6.8.0-59-generic 
root=UUID=a4811af7-d5ef-4599-ba77-d723e024b360 ro quiet splash vt.handoff=7
  RelatedPackageVersions:
   linux-restricted-modules-6.8.0-59-generic N/A
   linux-backports-modules-6.8.0-59-generic  N/A
   linux-firmware                            20240318.git3b128b60-0ubuntu2.11
  SourcePackage: linux
  UpgradeStatus: Upgraded to noble on 2024-08-27 (248 days ago)
  dmi.bios.date: 03/17/2025
  dmi.bios.release: 1.60
  dmi.bios.vendor: LENOVO
  dmi.bios.version: N22ET83W (1.60 )
  dmi.board.asset.tag: Not Available
  dmi.board.name: 20L8S8K30L
  dmi.board.vendor: LENOVO
  dmi.board.version: SDK0J40697 WIN
  dmi.chassis.asset.tag: No Asset Information
  dmi.chassis.type: 10
  dmi.chassis.vendor: LENOVO
  dmi.chassis.version: None
  dmi.ec.firmware.release: 1.23
  dmi.modalias: 
dmi:bvnLENOVO:bvrN22ET83W(1.60):bd03/17/2025:br1.60:efr1.23:svnLENOVO:pn20L8S8K30L:pvrThinkPadT480s:rvnLENOVO:rn20L8S8K30L:rvrSDK0J40697WIN:cvnLENOVO:ct10:cvrNone:skuLENOVO_MT_20L8_BU_Think_FM_ThinkPadT480s:
  dmi.product.family: ThinkPad T480s
  dmi.product.name: 20L8S8K30L
  dmi.product.sku: LENOVO_MT_20L8_BU_Think_FM_ThinkPad T480s
  dmi.product.version: ThinkPad T480s
  dmi.sys.vendor: LENOVO

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