Re: Pass transfer_buffer to gadget drivers

[Alan Stern <stern@rowland.harvard.edu>]

On Fri, 7 Jun 2019, Andrey Konovalov wrote:

> > > The problem is that I want to receive that data (from the data stage)
> > > from within my gadget driver module. But it's not passed to the
> > > setup() callback. And the question is: how do I do that then?
> >
> > I just caught up on this thread...
> >
> > The answer is simple: The gadget driver's setup() callback routine
> > submits a request for endpoint 0.  The Data Stage data is sent or
> > received (depending on the direction encoded in the Setup information)
> > by this request.
> 
> Ah, OK, got it, thanks!
> 
> Although while looking at the dummy_hcd implementation, I saw that it
> accesses usb->transfer_buffer in case USB_REQ_GET_STATUS in
> handle_control_request(), which is called right before the setup()
> callback is called. So the data already available there without any
> additional requests. Is this an implementation detail that is specific
> to dummy_hcd?

Yes, it is.  dummy-hcd is unusual in that it combines both a USB host
controller and a USB device controller in a single driver.

Normal UDC drivers do handle USB_REQ_GET_STATUS on their own without 
requiring the use of an explicit usb_request, because they handle the 
entire transfer internally and don't involve the gadget driver.  
However, they don't have access to any transfer_buffer; all they can do 
is exchange packets with the host.

Alan Stern