> > I have a USB 3.0 hub (not with me right now), which has either three or > > four USB 3.0 ports exposed, and seven USB 2.0 ports. The OS sees it as > > one USB 3.0 hub and two USB 2.0 hubs chained together. My guess is that > > the manufacturer wanted to say they had a "seven port USB 3.0 hub", but > > only four-port USB 3.0 hub chips were available, and they didn't have > > room in the hardware design or didn't want to pay for the second USB 3.0 > > hub chip. > > > > There's no real way to tell how port power is routed across the ports > > without doing some physical layout tests. I could see how they could > > meet the requirement in section 10.3.3 by pairing the USB 3.0 ports with > > either USB 2.0 hub. > > > > If they wanted to attach to the parent hub, they could physically expose > > three USB 3.0 ports, leave one port unexposed and not connected to any > > physical wires, and say the USB 3.0 hub has four ports. That ensures > > compatibility with section 10.3.3 while still allowing the USB 2.0 port > > to be used by the second-tier hub without exposing a USB 3.0-only port. > > > > However, that's technically violating the spirit of section, 10.3.3, and > > it's probably easier to pair the USB 3.0 ports with the child USB 2.0 > > hub. That would also allow them to expose all four USB 3.0 ports. > > In fact, it seems like this hub design is in actual violation of > Section 3.2.6.2 (not just the spirit): > > A USB 3.0 hub connects upstream as two devices; a SuperSpeed > hub on the SuperSpeed bus and a USB 2.0 hub on the USB 2.0 bus. > > Your hub connects as _two_ USB 2.0 hubs on the USB 2.0 bus, thus > appearing upstream as _three_ devices. The diagram in section D.1 of the xhci spec seems to imply that there can be additional USB2 hubs between the root hub and a USB3 hub. So if the USB3 ports are connected to the second tier USB2 port it might be conformant. David -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
