So I just learned that the majority of the Gigabyte X299 lineup has the rear USB 3.0 ports in a super weird setup:
1 USB 3.0 port upstream is naked with no hub, (maybe the BIOS port?) but the 3 other ports are using a Realtek USB 3.0 hub upstreaming to only 1 port from the chipset.
1 USB-C port goes straight to the controller, but the other goes to a hub splitting to 4 ports with upstream to the controller being a single port.
My biggest concern is UVC devices (or anything that doesn’t like hubs) and passthrough. UVC devices don’t like being behind a hub. I’ve experienced that first hand. Realistically this means the chipset can only provide a single port to the back that won’t have problems with UVC devices, but particularly if I passthrough half of the X299 chipset onboard XHCI controller. If someone has IOMMU groupings and USB tree data for something like the Aorus Gaming 9 or Gaming 7, I would like to know which port is the naked port, and which one is through the hub for the USB 3.0 ports. My suspicion is that it’s the BIOS port. If anyone’s using Windows, can you screenshot proof of that in Device Manager in a tree layout if you have onboard hubs?
Also, people using UVC devices, have you also had issues with it behind a hub both in your host OS and with your VMs to a controller card or with the chipset XHCI passed through? Have you had any other devices that have behaved weird because of motherboard onboard hubs? Specifically X299 and specifically motherboards that have this weird setup.
I realize this is asking a lot, but could save a lot of headaches for UVC device users or for anything that is very particular about not being behind a hub both for native and VMs. (low latency audio devices over USB perhaps)