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

[Juergen Gross <jgross@suse.com>]

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