Hi, >> >> ok, i will add code to UDC to instruct hardware to send NAK upon >> >> receiving invalid request on endpoint 0. Does it mean that UDC driver >> >> has to check for invalid request on endpoint 0? >> > >> > No. The UDC driver has no way to know whether a request is valid or >> > not. Read the description of the "setup" member of the >> > usb_gadget_driver structure in the header file. >> > >> >> I read that. The "setup" member of the usb_gadget_driver structure is >> pointing to fsg_setup, in file_storage.c. The fsg_setup() function >> handles the request on endpoint 0. So how could UDC driver know when >> to send NAK? > > When an invalid request is received, the gadget is supposed to send > STALL, not NAK. See the last two lines of the "setup" description: > > * USB byte order. Called in_interrupt; this may not sleep. Driver > * queues a response to ep0, or returns negative to stall. > > "Driver ... returns negative to stall." That's how the UDC driver > knows whether to send a STALL packet -- if the setup callback returns a > negative value. > > Also, it looks like you didn't read this paragraph in the description > of usb_ep_queue(): > > * Control endpoints ... after getting a setup() callback, the driver queues > * one response (even if it would be zero length). That enables the > * status ack, after transferring data as specified in the response. Setup > * functions may return negative error codes to generate protocol stalls. > * (Note that some USB device controllers disallow protocol stall responses > * in some cases.) When control responses are deferred (the response is > * written after the setup callback returns), then usb_ep_set_halt() may be > * used on ep0 to trigger protocol stalls. Depending on the controller, > * it may not be possible to trigger a status-stage protocol stall when the > * data stage is over, that is, from within the response's completion > * routine. > > Notice especially the fourth line. > > Alan Stern > Understand, UDC driver will call driver->setup(), and if the return value is negative, UDC driver has to set dev->protocol_stall = 1 and maybe call usb_ep_set_halt(). However, the hardware won't be able to send out zero length response. I think the purpose of zero length response is to get an ACK from the host. Thanks, victor -- 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
