Re: dwc3: unusual handling of setup requests with wLength == 0

[Thinh Nguyen <Thinh.Nguyen@synopsys.com>]

On Sun, Aug 20, 2023, Alan Stern wrote:
> On Sat, Aug 19, 2023 at 12:06:53AM +0000, Thinh Nguyen wrote:
> > On Fri, Aug 18, 2023, Alan Stern wrote:
> > > Actually I agree with you.  When a new SETUP packet arrives before the 
> > > old control transfer has finished, the UDC driver should cancel all 
> > > pending requests and then invoke the ->setup() callback.  (I don't think 
> > > there is a standard error code for the cancelled requests; net2280 seems 
> > > to use -EPROTO whereas dummy-hcd seems to use -EOVERFLOW.)
> > 
> > Those are very odd choice of error codes for cancelled request. Even
> > though the gadget side doesn't have very defined error codes, I try to
> > follow the equivalent doc from the host side
> > (driver-api/usb/error-codes.rst), which is -ECONNRESET.
> > 
> > Whenever I see -EPROTO, I associate that to a specific host error:
> > transaction error. For -EOVERFLOW, I think of babble errors.
> 
> Do you have a suggestion for an error code that all the UDCs should use 
> in this situation?  -ECONNRESET is currently being used for requests 
> that were cancelled by usb_ep_dequeue().  Would -EREMOTEIO be more 
> suitable for requests attached to an aborted control transfer?
> 

That works. It would be great if we can document the usb error codes for
gadget side and keep them consistent across UDC drivers. I think there
are only a few common errors:

* Request aborted
* Request dequeued
* STALL
* Data dropped (isoc only)

Any other?

Thanks,
Thinh