On Wed, 19 Aug 2015, Igor Kotrasinski wrote: > >> I would argue that there's no need to check gadget_is_dualspeed(); > >> bcdUSB should always be set to 0x0200. After all, the spec explicitly > >> permits USB-2.0 devices to run only at full speed. > > we should actually set it to 0x0210 so we get to send BOS descriptors > > :-) > > > If I understand it correctly then, gadget->max_speed isn't any indicator of > supported standard? That's right. There's almost no connection between the USB standard and the supported speeds. All you can depend on is this: If bcdUSB < 0x0200 then the device must run at low speed or full speed (it can't use high speed or SuperSpeed). If bcdUSB >= 0x0200 then the device must be able to connect at low speed or full speed (although it may not be able to do anything useful). It may also be able to run at high speed. If bcdUSB < 0x0300 then the device must run at low, full, or high speed (it can't use SuperSpeed). If bcdUSB >= 0x0300 then the device must run at SuperSpeed. Nothing else is guaranteed. > Either way, some else block definitely should be there. I don't follow why 0x0210 > is appropriate for all other gadget speeds; could you please, if possible, elaborate? As you can see from the above, devices with bcdUSB = 0x0210 are allowed to run at low, full, or high speed. Therefore it is an appropriate value. The extra meaning expressed by bcdUSB has to do with the set of descriptors provided by the device. With 0x0210, the device is obliged to provide BOS descriptors (as Felipe mentioned). With 0x0200, the device is obliged to provide an other-speed descriptor. 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
