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

Michael Grzeschik
2022-10-18T19:13:39Z

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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. :/

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

>> >
>> > There's a special case which dwc3 may give back requests early is the
>> > case of the device disconnecting. The requests should be returned with
>> > -ESHUTDOWN, and the gadget driver shouldn't be re-using the requests on
>> > de-initialization anyway.
>> >
>> > We should not issue End Transfer command just because of missed isoc. We
>> > may want issue End Transfer if the gadget driver is too slow and unable
>> > to feed requests in time (causing underrun and missed isoc) to resync
>> > with the host, but we already handle that.
>>
>> Hmm, isn't that what happens when we get into this
>> condition in dwc3_gadget_endpoint_trbs_complete():
>>
>> if (usb_endpoint_xfer_isoc(dep->endpoint.desc) &&
>> list_empty(&dep->started_list) &&
>> (list_empty(&dep->pending_list) || status == -EXDEV))
>> dwc3_stop_active_transfer(dep, true, true);
>>
>
>Yes, it's being handled there.
>
>> >
>> > I'm still not clear what's the problem you're seeing. Do you have the
>> > crash log? Tracepoints?
>> >
>>
>> Appreciate the support!
>>
>
>Thanks,
>Thinh

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