Xu, Andiry wrote: > Thanks for the ack. However, I found that when connect a USB3 device > (Buffalo HD-HXU3) via a USB2 cable to a xHCI host, it's bcdUSB > field is 0x0201. Since the check condition is bcdUSB >= 0x0210, > driver does not fetch BOS descriptors. Another USB3 device (Kingston > DT Ultimate) reports 0x0210 when connected via USB2 cable, and driver > fetches BOS descriptor. > > The value I used is from USB3 spec 9.2.6.6, which says "Devices with > a value of at least 0210H in the bcdUSB field of their device > descriptor shall support GetDescriptor (BOS descriptor) requests". This does not forbid _other_ devices to support the BOS descriptor. > However, I checked USB2 LPM spec Chapt 3, which says: "Devices that > support the BOS descriptor must have a bcdUSB value of 0201H or > larger." > > Is this a conflict? No. bcdUSB < 2.01: no BOS bcdUSB >= 2.01 and < 2.10: BOS optional bcdUSB >= 2.10: BOS required > Which value should I use, 0x0201 or 0x0210? 0x0201. No sane firmware writer will allow his 2.01 device to crash when it revceives a BOS request. But what about the insane ones? What does Windows do? Regards, Clemens -- 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
