Re: How should we handle isochronous underruns?

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On Thu, 18 Jul 2013, Clemens Ladisch wrote:

> In any case, there must be _some_ mechanism to explicitly restart
> a stream.  I do not really care if this is some URB flag or some
> function call.

I prefer a function call over the flag.  The function call can easily
be issued just once, but the completion routine would have to clear the
flag every time the URB gets used.

Maybe we can use usb_reset_endpoint() for this purpose after all.  It
is a perfect fit, because we want to tell the HCD to reset the
isochronous endpoint back to the "start of stream" state.

A search under drivers/ shows that only a few HCDs other than ehci
currently implement the endpoint_reset method: xhci, whci, dwc2, and
ozwpan.  It would not be hard to fix them up to ignore calls for
isochronous endpoints.

Any objections to this approach?

Alan Stern

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