On Wed, 13 Nov 2013, David Laight wrote: > > > 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. Sure, but that diagram shows _internal_ devices that are part of the computer. Sarah appears to be talking about an _external_ hub. Alan Stern -- 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
