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

[Paul Elder <paul.elder@ideasonboard.com>]

On Wed, Jan 09, 2019 at 02:06:31PM -0500, Alan Stern wrote:
> On Wed, 9 Jan 2019, Paul Elder wrote:
> 
> > A usb gadget function driver may or may not want to delay the status
> > stage of a control OUT request. An instance where it might want to is to
> > asynchronously validate the data of a class-specific request.
> > 
> > A function driver that wants an explicit status stage should set the
> > newly added explicit_status flag of the usb_request corresponding to the
> > data stage. Later on, the function driver can explicitly complete the
> > status stage by enqueueing a usb_request for ACK, or calling
> > usb_ep_set_halt() for STALL.
> > 
> > To support both explicit and implicit status stages, a UDC driver must
> > call the newly added usb_gadget_control_complete function right before
> > calling usb_gadget_giveback_request. To support the explicit status
> > stage, it might then check what stage the usb_request was queued in, and
> > for control IN ACK the host's zero-length data packet, or for control
> > OUT send a zero-length DATA1 ACK packet.
> > 
> > Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
> > v4 Acked-by: Alan Stern <stern@rowland.harvard.edu>
> > v1 Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> 
> This looks good and has passed my tests so far.

Good! Thank you :)

> Can you check your uvc
> changes using dummy_hcd with the patch below?

I'm not sure what to make of the test results. I get the same results
with or without the patch. Which I guess makes sense... in dummy_queue,
this is getting hit when the uvc function driver tries to complete the
delayed status:

	req = usb_request_to_dummy_request(_req);
	if (!_req || !list_empty(&req->queue) || !_req->complete)
		return -EINVAL;

So the delayed/explicit status stage is never completed, afaict.

Paul