Display manager fails needing pci rescan with thunderbolt eGPU

[Con Kolivas]

1.
No LSB modules are available.
Description: Ubuntu 24.04 LTS
Release: 24.04

2.
udev:
  Installed: 255.4-1ubuntu8
  Candidate: 255.4-1ubuntu8
  Version table:
 *** 255.4-1ubuntu8 500
        500 http://au.archive.ubuntu.com/ubuntu noble/main amd64 Packages
        100 /var/lib/dpkg/status

3.
Xorg should init via sddm, gd3m, or lightdm

4.
Display manager fails to init, remaining at console.

I have an eGPU device connected via thunderbolt
 ● Razer Core X
   ├─ type: peripheral
   ├─ name: Core X
   ├─ vendor: Razer
   ├─ uuid: 00c998e0-6fea-2701-ffff-ffffffffffff
   ├─ generation: Thunderbolt 3

It is mounted onto MSI MS-7E06 motherboard with a thunderbolt card. The card is correctly detected and enabled on bootup.

I have a NVIDIA 4070GTX installed on the eGPU device

VGA compatible controller: NVIDIA Corporation AD104 [GeForce RTX 4070] (rev a1)

I have installed the NVIDIA 550 drivers associated with this device

However, the presence of a GPU in an eGPU is not correctly detected after bootup. The various NVIDIA services at startup all present failure on bootup.

Sddm fails to start after multiple retries. Switching display manager to gdm3 or lightdm results in the same failure.

An `lspci` fails to show the device on the console.

I manually added a systemd daemon to scan the PCI bus before the display manager begins with:
echo "1" | sudo tee /sys/bus/pci/rescan > /dev/null

This then correctly identifies the device in the PCI bus, and then the display manager proceeds to start appropriately. eGPU functionality is limited to compute unless I manually insert xorg.conf.d rules, but that is an unrelated issue to do with limited eGPU support currently with xorg/wayland.

I believe the PCI bus needs to be scanned with udev rules when a thunderbolt device is detected/inserted.