On 08/19/2015 03:56 PM, Alan Stern wrote: > 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 > > I see now - it's the gadget layer that handles all relevant setup requests, and the controller is only concerned with an appropriate speed, so bcdUSB is only a matter of what descriptors the gadget layer supports. Many thanks to you and Balbi for explaining it, fixed patch is on the way. Igor Kotrasinski -- 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
