On Wed, Jan 11, 2012 at 11:17:00AM -0500, Alan Stern wrote: > On Wed, 11 Jan 2012, Alan Stern wrote: > > > On Tue, 10 Jan 2012, Sarah Sharp wrote: > > > > > When a SuperSpeed device is plugged into a high speed hub or an EHCI > > > port, it will show up as a high speed device with a BCD of 0x0201 or > > > 0x210 and it will contain a SuperSpeed Capabilities BOS descriptor. If > > > we see such a high speed device, warn the user that they should plug > > > their device into a USB 3.0 hub or xHCI root port. Only warn the user > > > if there is at least one SuperSpeed roothub available. > > > > > > We could attempt to fetch BOS descriptors for low or full speed devices, > > > in case the user plugs in a USB 3.0 device into an OHCI or UHCI-only > > > port, but it's possible those devices will choke on the request and fail > > > to be enumerated. Keep the current behavior of only asking for BOS > > > descriptors for devices that advertise a bcdUSB of 0x0201 and above. > > I forgot to mention this in the earlier email. > > The logic of this paragraph is wrong; we _do_ attempt to fetch BOS > descriptors for low- or full-speed devices. The only requirement is > that the bcdUSB value be >= 0x0201, and if that requirement is > satisfied then the device shouldn't choke on the request, regardless of > its current speed. Ah, ok, I see. I've just always thought that bcdUSB was directly related to the speed that the device was running at. At least, that's what I've seen when I've plugged USB 3.0 devices into EHCI ports. Sarah Sharp -- 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
