Re: [PATCH] usb: dwc3: gadget: don't dequeue requests on already disabled endpoints

[Michael Grzeschik <mgr@pengutronix.de>]

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On Mon, Mar 30, 2020 at 10:18:57AM +0300, Felipe Balbi wrote:
> 
> Hi,
> 
> Michael Grzeschik <mgr@pengutronix.de> writes:
> >> > dwc3_gadget_ep_disable gets called before the last request gets
> >> > dequeued.
> >> >
> >> > In __dwc3_gadget_ep_disable all started, pending and cancelled
> >> > lists for this endpoint will call dwc3_gadget_giveback in
> >> > dwc3_remove_requests.
> >> >
> >> > After that no list containing the afterwards dequed request,
> >> > therefor it is not necessary to run the dequeue routine.
> >> >
> >> > Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
> >> > ---
> >> > @Lars-Peter Clausen:
> >> >
> >> > This patch addresses the case that not queued requests get dequeued.
> >> > The only case that this happens seems on disabling the gadget.
> >> >
> >> >  drivers/usb/dwc3/gadget.c | 3 +++
> >> >  1 file changed, 3 insertions(+)
> >> >
> >> > diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> >> > index 9a6f741d1db0dc..5d4fa8d6c93e49 100644
> >> > --- a/drivers/usb/dwc3/gadget.c
> >> > +++ b/drivers/usb/dwc3/gadget.c
> >> > @@ -1609,6 +1609,9 @@ static int dwc3_gadget_ep_dequeue(struct usb_ep *ep,
> >> >  
> >> >  	trace_dwc3_ep_dequeue(req);
> >> >  
> >> > +	if (!(dep->flags & DWC3_EP_ENABLED))
> >> > +		return 0;
> >> 
> >> which driver is trying to call dequeue after the endpoint is disabled?
> >> Got some tracepoints of the problem happening?
> >
> > I see the case when using uvc-gadget.
> >
> > Look into uvc_v4l2_release in uvc_v4l2.c:
> >
> > uvc_function_disconnect
> >    composite_disconnect
> >       reset_config
> >          uvc_function_disable->usb_ep_disable
> >
> > uvcg_video_enable
> >    usb_ep_dequeue
> >       dwc3_gadget_ep_dequeue
> 
> Oh, I see what you mean. We get a disconnect, which disables the
> endpoints, which forces all requests to be dequeued. Now I remember why
> this exists: we giveback the requests from disconnect because not all
> gadget drivers will call usb_ep_dequeue() if simply told about the
> disconnect. Then UDC drivers have to be a little more careful and make
> sure that all requests are givenback.
> 
> In any case, why is it a problem to call usb_ep_dequeue()? Is it only
> because of that dev_err()? We could just remove that message,
> really.

In my case, it is not a problem removing the dev_err. The ep_dequeue
will only be called once for each request at the stream end. I don't
know about the case Lars has mentioned.

If we have to search all lists for the request every n times while in
traffic, only to find out that it was not enqueued, I think it would be
worth it to keep the dev_err and let these cases trigger so we have an
option to find and avoid/fix these.

> Eventually, I want to move more of this logic into UDC core so
> udc drivers can be simplified. For that work, though, first we would
> have to add a "generic" struct usb_ep_hw implementation and manage list
> of requests as part of UDC core as well.

I don't know about the cases you plan to abstract but it sounds
like a good idea to get some gadget logic out of the drivers.

Thanks,
Michael

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