From: Felipe Balbi <balbi@kernel.org>
To: Michael Grzeschik <mgr@pengutronix.de>
Cc: lars@metafoo.de, alexandru.Ardelean@analog.com,
linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
gregkh@linuxfoundation.org, bigeasy@linutronix.de,
m.olbrich@pengutronix.de, kernel@pengutronix.de
Subject: Re: [PATCH] usb: dwc3: gadget: don't dequeue requests on already disabled endpoints
Date: Mon, 30 Mar 2020 13:06:43 +0300 [thread overview]
Message-ID: <878sji2m30.fsf@kernel.org> (raw)
In-Reply-To: <20200330082548.GL27849@pengutronix.de>
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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.
Okay
> 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.
Yeah, I agree. That's why the dev_err() was placed there to start
with. In fact, I found a few gadget drivers which were trying to reuse a
request a allocated for EPxIN and queueing it to EPxOUT, clearly a
violation of request lifetime rules.
As for the search on three separate lists, I never considered this to be
a problem since it happens so infrequently. One thing we can do to make
it maybe faster, is convert those list_for_each_entry() to
list_for_each_entry_reverse(). I'm betting that there's higher
likelihood that the oldest request will be dequeued first, then again,
this needs to be profiled.
>> 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.
Yeah, this will take a lot of time, though. Hopefully it'll happen :-)
--
balbi
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prev parent reply other threads:[~2020-03-30 10:06 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-06 14:45 [PATCH] usb: dwc3: gadget: Handle dequeuing of non queued URB gracefully Alexandru Ardelean
2019-11-12 14:41 ` Michael Olbrich
2020-01-16 11:12 ` Ardelean, Alexandru
2020-01-16 13:05 ` Felipe Balbi
2020-01-16 13:24 ` [PATCH][RESEND] " Alexandru Ardelean
2020-01-30 12:02 ` Felipe Balbi
2020-03-10 13:22 ` Ardelean, Alexandru
2020-03-10 13:45 ` Lars-Peter Clausen
2020-03-10 14:07 ` Lars-Peter Clausen
2020-03-27 8:43 ` [PATCH] usb: dwc3: gadget: don't dequeue requests on already disabled endpoints Michael Grzeschik
2020-03-27 8:53 ` Sergei Shtylyov
2020-03-27 11:15 ` Andy Shevchenko
2020-03-27 9:14 ` Lars-Peter Clausen
2020-03-27 10:43 ` Michael Grzeschik
2020-03-27 10:55 ` Lars-Peter Clausen
2020-03-28 8:27 ` Felipe Balbi
2020-03-29 19:02 ` Michael Grzeschik
2020-03-30 7:18 ` Felipe Balbi
2020-03-30 8:25 ` Michael Grzeschik
2020-03-30 10:06 ` Felipe Balbi [this message]
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