Thunderbolt dock DisplayPort hotplug does not create a DRM connector on MacBookPro16,2

[grcatlin]

Summary

On a T2 MacBookPro16,2, a Dell WD19TB Thunderbolt Dock's USB and PCIe functions hotplug normally, but its attached display is never detected when the dock is connected after boot. The display works if the system is rebooted with the dock already connected.

This appears to be below the desktop environment: on runtime dock connection, the kernel does not emit a DRM/i915/DP event and all external i915 DP connectors remain disconnected.

• Model: MacBookPro16,2 (Intel Ice Lake / Iris Plus Graphics G7, 8086:8a53)
• Distribution: Fedora 44 Workstation
• Kernel: 7.1.5-201.t2.fc44.x86_64
• T2 kernel source: kernel-7.1.5-201.t2.fc44.src.rpm, Fedora COPR sharpenedblade/t2linux
• Dock: Dell WD19TB Thunderbolt Dock
• Dock NVM: 40.0
• GPU driver: i915

The dock appears on Thunderbolt domain 1 (0000:00:0d.3) and is authorized. Its negotiated link is 2 lanes at 20.0 Gb/s in each direction.

Steps to reproduce

1. Boot Fedora with the WD19TB disconnected.
2. Log in normally.
3. Connect the WD19TB with a display already attached to the dock.

• The dock appears as thunderbolt 1-1 and is authorized.
• PCIe hotplug succeeds and the dock xHCI controller is enumerated.
• USB devices behind the dock (Ethernet, audio, camera, keyboard/mouse) enumerate and work.
• No external display is detected.
• /sys/class/drm/card1-DP-{1..5}/status all remain disconnected.
• Kernel logs contain no i915, DRM, DisplayPort, AUX, link-training, or DP-tunnel event at dock connect time.

Rebooting while the dock remains connected initializes the display correctly. Unplugging and reconnecting after that again fails to detect the display.

The following was captured with journalctl -kf while unplugging, waiting approximately 8 seconds, and reconnecting the dock:

Aug 02 15:53:43 kernel: thunderbolt 1-1: device disconnected
Aug 02 15:53:43 kernel: pcieport 0000:00:07.2: pciehp: Slot(0-3): Link Down
Aug 02 15:53:51 kernel: thunderbolt 1-1: new device found, vendor=0xd4 device=0xb070
Aug 02 15:53:51 kernel: thunderbolt 1-1: Dell WD19TB Thunderbolt Dock
Aug 02 15:53:51 kernel: pcieport 0000:00:07.2: pciehp: Slot(0-3): Card present
Aug 02 15:53:51 kernel: pcieport 0000:00:07.2: pciehp: Slot(0-3): Link Up
Aug 02 15:53:52 kernel: pci 0000:75:00.0: [8086:15f0] type 00 class 0x0c0330 PCIe Endpoint
Aug 02 15:53:52 kernel: xhci_hcd 0000:75:00.0: xHCI Host Controller

After this, the expected USB devices enumerate. There are no corresponding i915, drm, DP, DisplayPort, or thunderbolt DP-tunnel messages.

DRM connector state after reconnect:

/sys/class/drm/card1-DP-1/status: disconnected
/sys/class/drm/card1-DP-2/status: disconnected
/sys/class/drm/card1-DP-3/status: disconnected
/sys/class/drm/card1-DP-4/status: disconnected
/sys/class/drm/card1-DP-5/status: disconnected
/sys/class/drm/card1-eDP-1/status: connected

Thunderbolt state after reconnect:

security=user
authorized=1
device_name=WD19TB Thunderbolt Dock
vendor_name=Dell
rx_speed=20.0 Gb/s
rx_lanes=2
tx_speed=20.0 Gb/s
tx_lanes=2
nvm_version=40.0

[grcatlin]

Tested 2026-08-03 with a different dock (HP USB hub IDs 03f0:079d / 03f0:579d; HP USB-C G5 Essential Dock).

On Fedora 44 with 7.1.5-201.t2.fc44.x86_64, unplugging and reconnecting this dock after login works: both external displays remain detected and enabled.

After reconnect:

• card1-DP-9: connected, enabled, 1920x1080
• card1-DP-11: connected, enabled, 1920x1080
• No devices exist under /sys/bus/thunderbolt/devices.

The hotplug kernel log shows USB hub/device teardown followed by normal re-enumeration, including the HP USB2.1/USB3.2 hubs and Realtek Ethernet. There were no i915, DRM, DisplayPort, Type-C, or Thunderbolt log messages at normal log level during this cycle.

This suggests the platform can hotplug displays through this dock's USB-C DP Alt Mode path. The WD19TB failure may be specific to Thunderbolt DP tunneling / dock initialization rather than generic i915 external-display hotplug.