Experience with Motherboards using onboard USB hubs?

Software & Operating Systems VFIO
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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)

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I’m sorry to ask but what does “UVC” stand for?

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USB Video Class. It’s for Webcams and USB capture cards.

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What webcam are you using that doesn’t like a hub? I’ve never heard this and have dozens of webcams (microsoft studio 1080p) plugged into computers all over my organization many into hubs.

The only concern I could see is plugging a power hungry device into a bus-powered hub and there not being enough current. Internal / root hubs are all self powered, so there should be plenty of power.

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I don’t have any solutions to your questions, but why would an OEM spend the extra money and time to implement a USB hub IC, instead of simply routing the traces from the chipset to the USB ports? I can’t imagine any advantages to this?

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I have absolutely no clue. Gigabyte chose to do it this way maybe because they wanted to brag about having 2 USB 3.0 internal headers.

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USB 3.0 UVC devices, maybe like the Logitech Brio, Magewell capture card, Epiphan AVio, etc…

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Dunno, I have an Elgato HD60s plugged into a hub on a Microsoft Surface, seems to do OK… But I’m not doing any fancy virtualization, just plain old windows 10.

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Then could it be weird hub + controller combos that cause incompatibility? Renesas + some hubs having issues?

To be safe, I’m getting a 4 port USB 3.0 internal header slot bracket because it goes through no hubs.

Edit: Looks like it’s all or nothing for the X299 controller, so USB controller portions are not partitioned like older chipsets.