[x86-64] XMOS USB DAC not instantly detected

Thank you for the suggestion

I used a USB stick with what is essentially the same LibreELEC installation and it works perfectly....wel the DAC hotplugs and is detected at boot.

lsusb
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 003: ID 0c45:671e Microdia Integrated_Webcam_HD
Bus 001 Device 005: ID 20b1:0002 XMOS Ltd XMOS USB Audio 2.0
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 003 Device 002: ID 05e3:0764 Genesys Logic, Inc. USB Storage
Bus 003 Device 003: ID 1a40:0101 Terminus Technology Inc. Hub
Bus 003 Device 004: ID 0bda:0129 Realtek Semiconductor Corp. RTS5129 Card Reader Controller
Bus 003 Device 005: ID 27c6:5301 Shenzhen Goodix Technology Co.,Ltd. Fingerprint Reader
Bus 003 Device 006: ID 0bda:b00b Realtek Semiconductor Corp. Realtek Bluetooth 4.2 Adapter
Bus 004 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub

ls /dev/snd/by-path/
pci-0000:04:00.1                pci-0000:04:00.3-usbv2-0:2:1.0
pci-0000:04:00.3-usb-0:2:1.0    pci-0000:04:00.6

That would suggest the DAC is good but my target laptop/LibreELEC installation has an issue.

I decided to get out all my old laptops, yes I am a sad persons that keeps those old devices.

I have 3 old laptops in addition to the one I want to use for LibreELEC. I tested each, two work perfectly in that the DAC was detected during boot, the other failed in the same way as the laptop I am targeting for LibreELEC.

[the reason I want to use the specific laptop for LibreELEC is because the screen "fell off" which doesn't matter as I will only ever connect it to a TV so it would be perfect for a media centre]

I dug out a Linux Mint installation on a USB stick and booted that on the failing laptops. After hotplugging the DAC I used hwinfo to locate what devices are involved

USB:XMOS device is attached to a USB hub which in turn is attached to a PCI hub controller. For both failing laptops the PCI connected USB Controller is an Intel Wildcat Point-LP USB XHCI controller, revision 0x03.

Doing the same investigation on the laptops that worked showed that the PCI connected Controllers were AMD devices (different ones)

I noticed that the report for the PCI connected controller reported that the activation command was "modprobe xhci-pci" but as thats a builtin I cannot remove/restart it

so, not quite a dead end but no success either

Of the two laptops which exhibit the problem I have fixed one (HP) by changing a bios setting. There was a system configuration setting "USB3.0 Configuration for Pre-OS" that was set to "enabled" which configured the USB port s to USB 3.0 controller. Changing this to "auto" means the USB ports are set to USB 2.0 in pre-boot and switched to 3.0 after boot. So auto fixed this laptop

No such setting on my target laptop (Lenovo) and so other settings for the USB port configuration.

So still stuck