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 11:23 AM, Gerd Hoffmann wrote:
> > > --- 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
> Hmm.  This is for IN transfers, notifying the host adapter "I have data
> for you, please hand me one (or more) USBPacket which I can fill".
>
> Why do you need it for OUT transfers too?  usb-host has copyed and
> queued up the data already, there is nothing to pass back ...
Aah, right. The packet->actual_length is filled during the copy. Is
this correct? What does libusb return for the single frames? I assume
this will be the amount which was sent out to the device, not the
size of the frame given to it.

> > - 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).
> Yes, endpoint callback would be more useful for this.
> PortOps needs this for remote wakeup implementation.
>
> >     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().
> You can call just call usb_handle_packet() multiple times, either
> calculate how often based on time and bandwidth, or continue calling
> until you get no more data back.
Understood. That's the polling case I mentioned above.


Juergen


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