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Date: Fri, 17 Aug 2012 09:07:01 +0200
From: Gerd Hoffmann <kraxel@redhat.com>
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Subject: Re: [Qemu-devel] 2 issues with qemu-master / 1.2 ehci code
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To: Hans de Goede <hdegoede@redhat.com>
Cc: "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>

  Hi,

> 2) happens when a packet fails, and the queue should be halted, in
> this case

Should we just cancel all queued packets on endpoint halts then?  If the
guest decides to go on we'll easily re-queue everything (with the
existing code).  If the guest does something else we don't have to do
anything special.

Not canceling, then trying to figure what the new state of the already
queued packets is could become tricky ...

> Another problem with failing packets is that hw/usb/core.c will
> happily execute the next packet in the ep queue, even though the spec
> says the ep-queue should be halted, giving the guest a chance to
> cancel transfers after the failed one without them ever executing.
> I've a poc patch fixing this too.

Indeed, the core should stop processing them.  Question is what to do
then.  If the host controller cancels all packets anyway we don't have
to do much extra work on the core.  Just stop processing on error and
implicitly un-halt the endpoint when the queue becomes empty.  Maybe
some extra state tracking and asserts() to catch bugs.

cheers,
  Gerd