> From: Alan Stern [mailto:stern@xxxxxxxxxxxxxxxxxxx] > Sent: Wednesday, June 27, 2012 7:18 AM > To: Paul Zimmerman > Cc: Sarah Sharp; Greg KH; linux-usb@xxxxxxxxxxxxxxx > Subject: RE: [PATCH] lsusb: Show USB 3.0 U1, U2, and LTM status. > > On Wed, 27 Jun 2012, Paul Zimmerman wrote: > > > > On the other hand, the USB-3 spec also says that when operating in a > > > USB-2 electrical environment, the device will "return appropriate > > > information according to the requirements laid out in the USB 2.0 > > > specification". This contradicts the requirement the bcdUSB value will > > > be 3.0. So maybe the manufacturers shouldn't be blamed. > > > > Just FYI, a device cannot have a bcdUSB of 0x300 in its device descriptor > > if it's not running at super speed, because a USB 3.0 device descriptor > > is incompatible with earlier versions, due to the bMaxPacketSize0 field > > being encoded as a power of 2 instead of a byte count. > > I don't see any problem. If bcdUSB is 0x0300 and the device is running > at, say, high speed then the maxpacket size for ep0 would be 64 bytes, > which would be represented by bMaxPacketSize0 = 6. See the description > of bMaxPacketSize0 in table 9-8 of the USB-3 spec. Ummm... how is a USB 2.0 host, released before the USB 3.0 spec was even written, supposed to know that? The device does not know what version of host it is connecting to. -- Paul -- 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
