Re: [Qemu-devel] uhci: cancel delay for unregistered queues

[Gerd Hoffmann]

  Hi,

>> The only fix I can think of is allocating a receive buffer inside
>> the UHCI code for read transfers, and copy the result over to the
>> guest memory when we are re-scanning the schedule, encounter the
>> completed td and are going to signal its completion to the guest.

> I could take a shot at writing a patch with the proposed fix, but I
> was sort of waiting on a reaction on the proposal first.
> 
> Gerd what do you think of my proposed fix ?

That should fix it indeed.  Yes, for uhci we can live with the overhead,
it's low bandwidth anyway.  No, I don't have a better idea.  Patch is
very welcome.

Luckily ehci + xhci have a better hardware design so the issue doesn't
exist there in the first place.  ehci has the IAAD handshake for
deactivating queue heads, which we are using to make sure any requests
are canceled before the guest releases the buffers.  xhci is completely
different anyway (and has control requests for deactivating endpoints
which also cancel all inflight transfers).

cheers,
  Gerd