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

[Thinh Nguyen]

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 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.

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.

I'm still not clear what's the problem you're seeing. Do you have the
crash log? Tracepoints?

BR,
Thinh