Vulkan does not detect eGPU connected to dock

Vulkan
1

Arch Linux, LGGram laptop hooked up to Thunderbolt 5 (TB5) docking station via Thunderbolt 4 (TB4) port. TB5 eGPU enclosure hooked up to docking station. eGPU enclosure contains Intel Arc B580 GPU. Vulkan fails to detect Arc B580: it doesn’t show up in, among others, vulkaninfo:

[dad@DadsGram Workspace]$ MESA_VK_DEVICE_SELECT=list vulkaninfo
selectable devices:
  GPU 0: 8086:a7a0 "Intel(R) Iris(R) Xe Graphics (RPL-P)" integrated GPU 0000:00:02.0

Any idea what I may be doing wrong? Here’s some other debugging info:

[dad@DadsGram ~]$ lspci | grep VGA
00:02.0 VGA compatible controller: Intel Corporation Raptor Lake-P [Iris Xe Graphics] (rev 04)
41:00.0 VGA compatible controller: Intel Corporation Battlemage G21 [Arc B580]

[dad@DadsGram ~]$ lshw
...
*-display
     description: VGA compatible controller
     product: Raptor Lake-P [Iris Xe Graphics]
     vendor: Intel Corporation
     physical id: 2
     bus info: pci@0000:00:02.0
     logical name: /dev/fb0
     version: 04
     width: 64 bits
     clock: 33MHz
     capabilities: vga_controller bus_master cap_list rom fb
     configuration: depth=32 driver=i915 latency=0 resolution=2560,1600
     resources: iomemory:600-5ff iomemory:400-3ff irq:211 memory:603c000000-603cffffff memory:4000000000-400fffffff ioport:2000(size=64) memory:c0000-dffff memory:4010000000-4016ffffff memory:4020000000-40ffffffff
...
*-display
     description: VGA compatible controller
     product: Battlemage G21 [Arc B580]
     vendor: Intel Corporation
     physical id: 0
     bus info: pci@0000:41:00.0
     version: 00
     width: 64 bits
     clock: 33MHz
     capabilities: vga_controller bus_master cap_list rom
     configuration: driver=xe latency=0
     resources: irq:0 memory:52000000-52ffffff

Interestingly, no such thing happens when connecting eGPU directly to laptop’s second TB4 port. (There’s other funny stuff that happens in that scenario, though Vulkan does detect both GPUs just fine; see also discussions here and here.)

2

Cross-ref: