Re: [PATCH v5 4/6] usb: gadget: add mechanism to specify an explicit status stage

[Alan Stern]

On Fri, 18 Jan 2019, Paul Elder wrote:

> > > I meant the functions (procedures) in the function driver, so the setup
> > > handler (uvc_function_setup), the completion handler
> > > (uvc_function_ep0_complete), and the status sender (uvc_send_response),
> > > although the last one actually sends the data stage for control IN.
> > > So after the status is sent on the uvc gadget driver's end, its
> > > completion handler is called again without the setup handler being
> > > called beforehand and I cant figure out why.
> > 
> > Isn't this what you should expect?  Every usb_request, if it is queued
> > successfully, eventually gets a completion callback.  That promise is
> > made by every UDC driver; it's part of the gadget API.  So for a
> > control transfer with a data stage, you expect to have:
> > 
> > 	Setup handler called
> > 	Data-stage request submitted
> > 	Data-stage request completion callback
> > 	Status-stage request submitted
> > 	Status-stage request completion callback
> > 
> > Thus, two completion callbacks but only one setup callback.
> 
> omg how did I not notice this :/
> 
> I guess I have to fix the uvc function driver so it works with that.
> musb doesn't call the status stage completion callback though; not that
> it does anything so it seems fine to me, but indeed the function driver
> has to be ready for it if it is called.

musb _has_ to call the status-stage completion callback.  As just one
reason, if the explicit_status flag isn't set then that callback is
responsible for deallocating the status request.  Without it, the
status request will leak.

Alan Stern