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

Thinh Nguyen
2022-10-18T22:45:47Z

On Tue, Oct 18, 2022, Michael Grzeschik wrote:
> Hi Thinh,
>
> 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@motorola.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.

> 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?

Thanks!
Thinh