A single USB xHCI controller is not bottlenecked to 480Mbps globally, since the multiple ports aren't actually sharing a 2.0 physical layer. The "root hub" isn'

A single USB xHCI controller is not bottlenecked to 480Mbps globally, since the multiple ports aren't actually sharing a 2.0 physical layer. The "root hub" isn't like a normal hub in that sense. So you don't need a controller per port, as long as the controller is designed to support this. Quoting the xHCI spec: > In past generations of USB host controller implementations, there was a 1:1 correspondence between a host controller interface and USB bandwidth. The xHCI diverges from this model in that it enables vendors to tailor the bandwidth available through its root hub ports to the needs of the vendor’s target application space. The xHCI can support the legacy model where the bandwidth of a single USB is shared across all its root hub ports, a “bus per port” model where the full bandwidth of a USB is available on every root hub port, or any combination in between. I believe most real 3.0 implementations do it per port, or at least have a bunch of instances, because it doesn't really make any sense to do otherwise. You're not really saving much money by somehow having a global bottleneck equal to the PHY bandwidth. Of course, it's possible for the controller to be bottlenecked upstream in some other way (e.g. by DMA bandwidth), but it would be very weird to find an xHCI controller with a single 480Mbps domain for all 2.0 ports IMO.