Re: [PATCH v3 2/6] usb: dwc3: gadget: cancel requests instead of release after missed isoc

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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@xxxxxxxxxxxx>
> > > >
> > > > 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@xxxxxxxxxxxxxx/__;!!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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