Comment 16 for bug 1939638

See the attached dmesg output. Here's the relevant line:

[ 37.400119] usb usb1-port4: couldn't allocate usb_device

The lspci utility is not available on Ubuntu Core 20, but when I boot Ubuntu Desktop 20.04 LTS from a live USB drive it yields the following output on the affected machine:

$ lspci -nn | grep -i USB
00:15.0 USB controller [0c03]: Intel Corporation Celeron N3350/Pentium N4200/Atom E3900 Series USB xHCI [8086:5aa8] (rev 0b)

Some additional observations:

1. Very, very occasionally, the "couldn't allocate usb_device" line won't be present in dmesg output and in this case the affected USB device *will* work immediately after boot. So this does seem to be a race condition of some kind.
2. I ran a quick check just in case: this is still present on the latest pc-kernel Snap update from a couple of days ago on the 20/stable channel (5.4.0-107.121.1).
3. I can confirm that the unbind-bind operation posted by tgs-bonn above makes the affected USB devices appear on my system as well:

$ echo '0000:00:15.0' | sudo tee /sys/bus/pci/drivers/xhci_hcd/unbind
$ sleep 1
$ echo '0000:00:15.0' | sudo tee /sys/bus/pci/drivers/xhci_hcd/bind