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From: Hans Petter Selasky <hselasky@c2i.net>
To: Seb <sebastien.b@swissinfo.org>
Date: Sat, 28 May 2005 15:31:10 +0200
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Cc: freebsd-usb@freebsd.org
Subject: Re: usbd_bulk_transfer returns 1 (USBD_IN_PROGRESS) ?!
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On Friday 27 May 2005 13:31, Seb wrote:
> Ok, I understood the problem.
> But I didn't fix it with mutexes, I used semaphores instead.
> I initialize a semaphore with a value equal to 1 and then, before the USB
> transfers, I do :
while(entered)
{
> mtx_unlock(&Giant);
> sema_wait(&sc->usb_tx_sema);
> mtx_lock(&Giant);
}
  entered = 1;
> And after the USB transfers :
> sema_post(&sc->usb_tx_sema);
  entered = 0;

> Is this OK ? 

I think it is better you use "sx_xlock", "sx_xunlock" and "sx_init". 
See "man sx".

> Apparently it has solved the problem, the driver now sustains 
> heavy network load :)
> I wouln't like to use asynchronous transfers, they make the code hard to
> read and would require all users to recompile their kernels to install your
> USB driver...

You, can do asynchronous transfers with the existing USB driver too. But to do 
what you want to do, the code will be a little more complicated, because the 
existing USB-API wasn't designed to handle that. Just make a wrapper for 
"usbd_bulk_transfer()":

my_bulk_transfer(sc, xfer):
{
  if(started == 0)
  {
    m = dequeue packet;
    if(m == NULL) return;

    prepend m;

    started = 1;

    err = usbd_transfer();
    if(err)
    {
        started = 0;
    }
  }
}

your_callback(xfer,...,error):
{
  started = 0;

  if(error == 0) {
    my_bulk_transfer(sc, xfer); 
    /* calling usbd_transfer() 
     * from callback is allowed 
     */
  }
}

If you do things via callback you can remove "sc->tx_queues[]" and associated 
functions. I think you will get better performance using callbacks. And most 
importantly, you are no longer blocking the callers of those functions that 
send packets.

--HPS