Date:   Wed, 19 Oct 2022 08:46:48 +0200
From:   Michael Grzeschik <mgr@...gutronix.de>
To:     Thinh Nguyen <Thinh.Nguyen@...opsys.com>
Cc:     Dan Vacura <w36195@...orola.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        Daniel Scally <dan.scally@...asonboard.com>,
        Jeff Vanhoof <qjv001@...orola.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jonathan Corbet <corbet@....net>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Felipe Balbi <balbi@...nel.org>,
        Paul Elder <paul.elder@...asonboard.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH v3 2/6] usb: dwc3: gadget: cancel requests instead of
 release after missed isoc

Hi Thinh,

On Tue, Oct 18, 2022 at 10:45:16PM +0000, Thinh Nguyen wrote:
>On Tue, Oct 18, 2022, Michael Grzeschik wrote:
>> On Tue, Oct 18, 2022 at 06:45:40PM +0000, Thinh Nguyen wrote:
>> > On Mon, Oct 17, 2022, Dan Vacura wrote:
>> > > On Mon, Oct 17, 2022 at 09:30:38PM +0000, Thinh Nguyen wrote:
>> > > > On Mon, Oct 17, 2022, Dan Vacura wrote:
>> > > > > From: Jeff Vanhoof <qjv001@...orola.com>
>> > > > >
>> > > > > arm-smmu related crashes seen after a Missed ISOC interrupt when
>> > > > > no_interrupt=1 is used. This can happen if the hardware is still using
>> > > > > the data associated with a TRB after the usb_request's ->complete call
>> > > > > has been made.  Instead of immediately releasing a request when a Missed
>> > > > > ISOC interrupt has occurred, this change will add logic to cancel the
>> > > > > request instead where it will eventually be released when the
>> > > > > END_TRANSFER command has completed. This logic is similar to some of the
>> > > > > cleanup done in dwc3_gadget_ep_dequeue.
>> > > >
>> > > > This doesn't sound right. How did you determine that the hardware is
>> > > > still using the data associated with the TRB? Did you check the TRB's
>> > > > HWO bit?
>> > >
>> > > The problem we're seeing was mentioned in the summary of this patch
>> > > series, issue #1. Basically, with the following patch
>> > > https://urldefense.com/v3/__https://patchwork.kernel.org/project/linux-usb/patch/20210628155311.16762-6-m.grzeschik@pengutronix.de/__;!!A4F2R9G_pg!aSNZ-IjMcPgL47A4NR5qp9qhVlP91UGTuCxej5NRTv8-FmTrMkKK7CjNToQQVEgtpqbKzLU2HXET9O226AEN$
>> > > integrated a smmu panic is occurring on our Android device with the 5.15
>> > > kernel which is:
>> > >
>> > >     <3>[  718.314900][  T803] arm-smmu 15000000.apps-smmu: Unhandled arm-smmu context fault from a600000.dwc3!
>> > >
>> > > The uvc gadget driver appears to be the first (and only) gadget that
>> > > uses the no_interrupt=1 logic, so this seems to be a new condition for
>> > > the dwc3 driver. In our configuration, we have up to 64 requests and the
>> > > no_interrupt=1 for up to 15 requests. The list size of dep->started_list
>> > > would get up to that amount when looping through to cleanup the
>> > > completed requests. From testing and debugging the smmu panic occurs
>> > > when a -EXDEV status shows up and right after
>> > > dwc3_gadget_ep_cleanup_completed_request() was visited. The conclusion
>> > > we had was the requests were getting returned to the gadget too early.
>> >
>> > As I mentioned, if the status is updated to missed isoc, that means that
>> > the controller returned ownership of the TRB to the driver. At least for
>> > the particular request with -EXDEV, its TRBs are completed. I'm not
>> > clear on your conclusion.
>> >
>> > Do we know where did the crash occur? Is it from dwc3 driver or from uvc
>> > driver, and at what line? It'd great if we can see the driver log.
>> >
>> > >
>> > > >
>> > > > The dwc3 driver would only give back the requests if the TRBs of the
>> > > > associated requests are completed or when the device is disconnected.
>> > > > If the TRB indicated missed isoc, that means that the TRB is completed
>> > > > and its status was updated.
>> > >
>> > > Interesting, the device is not disconnected as we don't get the
>> > > -ESHUTDOWN status back and with this patch in place things continue
>> > > after a -EXDEV status is received.
>> > >
>> >
>> > Actually, minor correction here: a recent change
>> > b44c0e7fef51 ("usb: dwc3: gadget: conditionally remove requests")
>> > changed -ESHUTDOWN request status to -ECONNRESET when disable endpoint.
>> > This doesn't look right.
>> >
>> > While disabling endpoint may also apply for other cases such as
>> > switching alternate interface in addition to disconnect, -ESHUTDOWN
>> > seems more fitting there.
>> >
>> > Hi Michael,
>> >
>> > Can you help clarify for the change above? This changed the usage of
>> > requests. Now requests returned by disconnection won't be returned as
>> > -ESHUTDOWN.
>>
>> When writing the patch, I was looking into
>> Documentation/driver-api/usb/error-codes.rst.
>>
>> After looking into it today, I see that ESHUTDOWN should be send on
>> ep_disable (device disable) and ECONNRESET on stop_active_transfer.
>> So I probably just mixed them up, while writing the patch. :/
>>
>
>I think you mean ECONNRESET for ep_dequeue()?
>dwc3_stop_active_transfer() is called for both scenarios.

No, I meant dwc3_stop_active_transfer*s*.
On ep_dequeue the request status is already ECONNRESET.

>> The followup patch would then just be to swap the status results of
>> __dwc3_gadget_ep_disable and dwc3_stop_active_transfers on the
>> dwc3_remove_requests call.
>>
>> Michael
>
>Can you help make a fix?

Sure, I will write a patch.

Thanks,
Michael

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