/**********************************************************************

* spcaReducePacketSize

* Function Fixes the bandwidth problem that occurs

* when other USB devices are on the same host controller bus as the

* camera by gradually lowering the bandwidth requirements of the driver.

* It works even when other USB devices are present on the same

* host controller bus as the camera. 

*

* Problem

* When other USB devices are present on the same host controller

* bus as the camera, the bandwidth requirements of the spca5xx driver

* are not being met. The spca5xx driver is asking for more bandwidth

* than is available which results in the following error messages:

*

* No space left on device

* can't open /dev/video0: No space left on device.

* usb_submit_urb(0) ret -28

*

* 

* Many thanks to all the wonderful people contributing to this project.

*

* Great work!

* vodunvibe [AT] NO@SPAM.PLEASE yahoo DOT com

* 2006-08-27

* 

***********************************************************************/

static int spcaReducePacketSize(struct usb_spca50x *spca50x, int n, int err)

{

    int size=896, fx, i;

    err("spcaReducePacketSize: vodunvibe - The usb_submit_urb(%d) transfer request submission failed - You probably have another device sharing the same USB Host Controller Bus as your camera. Try using another USB port, on a different host controller bus.", n);

    while (err == -ENOSPC && size >= 0) {

	    err("spcaReducePacketSize: vodunvibe - Lowering the bandwidth requirements - New packet size (%d) ", size);

        spca50x_set_packet_size(spca50x, size);

    	spca50x->sbuf[n].urb->transfer_buffer_length = spca50x->packet_size * FRAMES_PER_DESC;

    	for (fx = 0; fx < FRAMES_PER_DESC; fx++) {

    	    spca50x->sbuf[n].urb->iso_frame_desc[fx].offset = spca50x->packet_size * fx;

    	    spca50x->sbuf[n].urb->iso_frame_desc[fx].length = spca50x->packet_size;

    	}

        size-=128;

#if LINUX_VERSION_CODE > KERNEL_VERSION(2,5,41)

    	err = usb_submit_urb(spca50x->sbuf[n].urb, GFP_KERNEL);

#else

    	err = usb_submit_urb(spca50x->sbuf[n].urb);

#endif

    }

	if (!err) {

      for (i = 0; i < SPCA50X_NUMSBUF; i++) {

    	spca50x->sbuf[i].urb->transfer_buffer_length = spca50x->packet_size * FRAMES_PER_DESC;

    	for (fx = 0; fx < FRAMES_PER_DESC; fx++) {

    	    spca50x->sbuf[i].urb->iso_frame_desc[fx].offset = spca50x->packet_size * fx;

    	    spca50x->sbuf[i].urb->iso_frame_desc[fx].length = spca50x->packet_size;

    	}

      }

    }

    return err;

}