Re: [Xen-devel] [Patch RFC 2/4] usb: add flag to USBPacket to request complete callback after isoc transfer

[Juergen Gross <jgross@xxxxxxxx>]

On 07/17/2015 10:12 AM, Gerd Hoffmann wrote:
> On Do, 2015-07-16 at 17:47 +0200, Juergen Gross wrote:
> > In order to avoid having to poll for the result of an iso transfer
> > add the possibility to request the "complete" callback which is being
> > used for bulk transfers as well.
> Sorry for the late notice (didn't do much usb coding recently and forgot
> about it):  We actually _have_ a notification mechanism already:
> usb_wakeup(USBEndpoint *ep, int streamid). That will trigger a
> USBPortOps->wakeup callback in the host adapter emulation.
>
> So, the usb-host change should be as simple as this:
>
> --- a/hw/usb/host-libusb.c
> +++ b/hw/usb/host-libusb.c
> @@ -451,6 +451,7 @@ static void usb_host_req_complete_iso(struct
> libusb_transfer *transfer)
>       }
>       if (xfer->ring->ep->pid == USB_TOKEN_IN) {
>           QTAILQ_INSERT_TAIL(&xfer->ring->copy, xfer, next);
> +        usb_wakeup(xfer->ring->ep, 0);
>       } else {
>           QTAILQ_INSERT_TAIL(&xfer->ring->unused, xfer, next);
>       }
Hmm, I can see the benefit of this call to avoid polling.

OTOH I don't see how to find the packages already processed via this
mechanism. To help in my case I'd need:

- the call being made in the else clause
- some way to have a package reference in the endpoint (assuming
  to use the bus .endpoint_wakeup callback which is called by
  usb_wakeup(), too).
  The problem here is that host-libusb.c would call usb_wakeup()
  not for each packet, but for each libusb I/O, which is combining
  multiple packets given to usb_handle_packet().


Juergen


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