sound/usb/line6/playback.c - kernel/quantenna - Git at Google

 /*
  * Line 6 Linux USB driver
  *
  * Copyright (C) 2004-2010 Markus Grabner (grabner@icg.tugraz.at)
  *
  *	This program is free software; you can redistribute it and/or
  *	modify it under the terms of the GNU General Public License as
  *	published by the Free Software Foundation, version 2.
  *
  */

 #include <linux/slab.h>
 #include <sound/core.h>
 #include <sound/pcm.h>
 #include <sound/pcm_params.h>

 #include "capture.h"
 #include "driver.h"
 #include "pcm.h"
 #include "playback.h"

 /*
 	Software stereo volume control.
 */
 static void change_volume(struct urb *urb_out, int volume[],
 			  int bytes_per_frame)
 {
 	int chn = 0;

 	if (volume[0] == 256 && volume[1] == 256)
 		return;		/* maximum volume - no change */

 	if (bytes_per_frame == 4) {
 		__le16 *p, *buf_end;

 		p = (__le16 *)urb_out->transfer_buffer;
 		buf_end = p + urb_out->transfer_buffer_length / sizeof(*p);

 		for (; p < buf_end; ++p) {
 			short pv = le16_to_cpu(*p);
 			int val = (pv * volume[chn & 1]) >> 8;
 			pv = clamp(val, -0x8000, 0x7fff);
 			*p = cpu_to_le16(pv);
 			++chn;
 		}
 	} else if (bytes_per_frame == 6) {
 		unsigned char *p, *buf_end;

 		p = (unsigned char *)urb_out->transfer_buffer;
 		buf_end = p + urb_out->transfer_buffer_length;

 		for (; p < buf_end; p += 3) {
 			int val;

 			val = p[0] + (p[1] << 8) + ((signed char)p[2] << 16);
 			val = (val * volume[chn & 1]) >> 8;
 			val = clamp(val, -0x800000, 0x7fffff);
 			p[0] = val;
 			p[1] = val >> 8;
 			p[2] = val >> 16;
 			++chn;
 		}
 	}
 }

 /*
 	Create signal for impulse response test.
 */
 static void create_impulse_test_signal(struct snd_line6_pcm *line6pcm,
 				       struct urb *urb_out, int bytes_per_frame)
 {
 	int frames = urb_out->transfer_buffer_length / bytes_per_frame;

 	if (bytes_per_frame == 4) {
 		int i;
 		short *pi = (short *)line6pcm->prev_fbuf;
 		short *po = (short *)urb_out->transfer_buffer;

 		for (i = 0; i < frames; ++i) {
 			po[0] = pi[0];
 			po[1] = 0;
 			pi += 2;
 			po += 2;
 		}
 	} else if (bytes_per_frame == 6) {
 		int i, j;
 		unsigned char *pi = line6pcm->prev_fbuf;
 		unsigned char *po = urb_out->transfer_buffer;

 		for (i = 0; i < frames; ++i) {
 			for (j = 0; j < bytes_per_frame / 2; ++j)
 				po[j] = pi[j];

 			for (; j < bytes_per_frame; ++j)
 				po[j] = 0;

 			pi += bytes_per_frame;
 			po += bytes_per_frame;
 		}
 	}
 	if (--line6pcm->impulse_count <= 0) {
 		((unsigned char *)(urb_out->transfer_buffer))[bytes_per_frame -
 							      1] =
 		    line6pcm->impulse_volume;
 		line6pcm->impulse_count = line6pcm->impulse_period;
 	}
 }

 /*
 	Add signal to buffer for software monitoring.
 */
 static void add_monitor_signal(struct urb *urb_out, unsigned char *signal,
 			       int volume, int bytes_per_frame)
 {
 	if (volume == 0)
 		return;		/* zero volume - no change */

 	if (bytes_per_frame == 4) {
 		__le16 *pi, *po, *buf_end;

 		pi = (__le16 *)signal;
 		po = (__le16 *)urb_out->transfer_buffer;
 		buf_end = po + urb_out->transfer_buffer_length / sizeof(*po);

 		for (; po < buf_end; ++pi, ++po) {
 			short pov = le16_to_cpu(*po);
 			short piv = le16_to_cpu(*pi);
 			int val = pov + ((piv * volume) >> 8);
 			pov = clamp(val, -0x8000, 0x7fff);
 			*po = cpu_to_le16(pov);
 		}
 	}

 	/*
 	   We don't need to handle devices with 6 bytes per frame here
 	   since they all support hardware monitoring.
 	 */
 }

 /*
 	Find a free URB, prepare audio data, and submit URB.
 	must be called in line6pcm->out.lock context
 */
 static int submit_audio_out_urb(struct snd_line6_pcm *line6pcm)
 {
 	int index;
 	int i, urb_size, urb_frames;
 	int ret;
 	const int bytes_per_frame = line6pcm->properties->bytes_per_frame;
 	const int frame_increment =
 		line6pcm->properties->rates.rats[0].num_min;
 	const int frame_factor =
 		line6pcm->properties->rates.rats[0].den *
 		(USB_INTERVALS_PER_SECOND / LINE6_ISO_INTERVAL);
 	struct urb *urb_out;

 	index =
 	    find_first_zero_bit(&line6pcm->out.active_urbs, LINE6_ISO_BUFFERS);

 	if (index < 0 || index >= LINE6_ISO_BUFFERS) {
 		dev_err(line6pcm->line6->ifcdev, "no free URB found\n");
 		return -EINVAL;
 	}

 	urb_out = line6pcm->out.urbs[index];
 	urb_size = 0;

 	for (i = 0; i < LINE6_ISO_PACKETS; ++i) {
 		/* compute frame size for given sampling rate */
 		int fsize = 0;
 		struct usb_iso_packet_descriptor *fout =
 		    &urb_out->iso_frame_desc[i];

 		fsize = line6pcm->prev_fsize;
 		if (fsize == 0) {
 			int n;

 			line6pcm->out.count += frame_increment;
 			n = line6pcm->out.count / frame_factor;
 			line6pcm->out.count -= n * frame_factor;
 			fsize = n * bytes_per_frame;
 		}

 		fout->offset = urb_size;
 		fout->length = fsize;
 		urb_size += fsize;
 	}

 	if (urb_size == 0) {
 		/* can't determine URB size */
 		dev_err(line6pcm->line6->ifcdev, "driver bug: urb_size = 0\n");
 		return -EINVAL;
 	}

 	urb_frames = urb_size / bytes_per_frame;
 	urb_out->transfer_buffer =
 	    line6pcm->out.buffer +
 	    index * LINE6_ISO_PACKETS * line6pcm->max_packet_size;
 	urb_out->transfer_buffer_length = urb_size;
 	urb_out->context = line6pcm;

 	if (test_bit(LINE6_STREAM_PCM, &line6pcm->out.running) &&
 	    !test_bit(LINE6_FLAG_PAUSE_PLAYBACK, &line6pcm->flags)) {
 		struct snd_pcm_runtime *runtime =
 		    get_substream(line6pcm, SNDRV_PCM_STREAM_PLAYBACK)->runtime;

 		if (line6pcm->out.pos + urb_frames > runtime->buffer_size) {
 			/*
 			   The transferred area goes over buffer boundary,
 			   copy the data to the temp buffer.
 			 */
 			int len;

 			len = runtime->buffer_size - line6pcm->out.pos;

 			if (len > 0) {
 				memcpy(urb_out->transfer_buffer,
 				       runtime->dma_area +
 				       line6pcm->out.pos * bytes_per_frame,
 				       len * bytes_per_frame);
 				memcpy(urb_out->transfer_buffer +
 				       len * bytes_per_frame, runtime->dma_area,
 				       (urb_frames - len) * bytes_per_frame);
 			} else
 				dev_err(line6pcm->line6->ifcdev, "driver bug: len = %d\n",
 					len);
 		} else {
 			memcpy(urb_out->transfer_buffer,
 			       runtime->dma_area +
 			       line6pcm->out.pos * bytes_per_frame,
 			       urb_out->transfer_buffer_length);
 		}

 		line6pcm->out.pos += urb_frames;
 		if (line6pcm->out.pos >= runtime->buffer_size)
 			line6pcm->out.pos -= runtime->buffer_size;

 		change_volume(urb_out, line6pcm->volume_playback,
 			      bytes_per_frame);
 	} else {
 		memset(urb_out->transfer_buffer, 0,
 		       urb_out->transfer_buffer_length);
 	}

 	spin_lock_nested(&line6pcm->in.lock, SINGLE_DEPTH_NESTING);
 	if (line6pcm->prev_fbuf) {
 		if (test_bit(LINE6_STREAM_IMPULSE, &line6pcm->out.running)) {
 			create_impulse_test_signal(line6pcm, urb_out,
 						   bytes_per_frame);
 			if (test_bit(LINE6_STREAM_PCM, &line6pcm->in.running)) {
 				line6_capture_copy(line6pcm,
 						   urb_out->transfer_buffer,
 						   urb_out->
 						   transfer_buffer_length);
 				line6_capture_check_period(line6pcm,
 					urb_out->transfer_buffer_length);
 			}
 		} else {
 			if (!(line6pcm->line6->properties->capabilities & LINE6_CAP_HWMON)
 			    && line6pcm->out.running && line6pcm->in.running)
 				add_monitor_signal(urb_out, line6pcm->prev_fbuf,
 						   line6pcm->volume_monitor,
 						   bytes_per_frame);
 		}
 		line6pcm->prev_fbuf = NULL;
 		line6pcm->prev_fsize = 0;
 	}
 	spin_unlock(&line6pcm->in.lock);

 	ret = usb_submit_urb(urb_out, GFP_ATOMIC);

 	if (ret == 0)
 		set_bit(index, &line6pcm->out.active_urbs);
 	else
 		dev_err(line6pcm->line6->ifcdev,
 			"URB out #%d submission failed (%d)\n", index, ret);

 	return 0;
 }

 /*
 	Submit all currently available playback URBs.
 	must be called in line6pcm->out.lock context
  */
 int line6_submit_audio_out_all_urbs(struct snd_line6_pcm *line6pcm)
 {
 	int ret = 0, i;

 	for (i = 0; i < LINE6_ISO_BUFFERS; ++i) {
 		ret = submit_audio_out_urb(line6pcm);
 		if (ret < 0)
 			break;
 	}

 	return ret;
 }

 /*
 	Callback for completed playback URB.
 */
 static void audio_out_callback(struct urb *urb)
 {
 	int i, index, length = 0, shutdown = 0;
 	unsigned long flags;
 	struct snd_line6_pcm *line6pcm = (struct snd_line6_pcm *)urb->context;
 	struct snd_pcm_substream *substream =
 	    get_substream(line6pcm, SNDRV_PCM_STREAM_PLAYBACK);

 #if USE_CLEAR_BUFFER_WORKAROUND
 	memset(urb->transfer_buffer, 0, urb->transfer_buffer_length);
 #endif

 	line6pcm->out.last_frame = urb->start_frame;

 	/* find index of URB */
 	for (index = 0; index < LINE6_ISO_BUFFERS; index++)
 		if (urb == line6pcm->out.urbs[index])
 			break;

 	if (index >= LINE6_ISO_BUFFERS)
 		return;		/* URB has been unlinked asynchronously */

 	for (i = 0; i < LINE6_ISO_PACKETS; i++)
 		length += urb->iso_frame_desc[i].length;

 	spin_lock_irqsave(&line6pcm->out.lock, flags);

 	if (test_bit(LINE6_STREAM_PCM, &line6pcm->out.running)) {
 		struct snd_pcm_runtime *runtime = substream->runtime;

 		line6pcm->out.pos_done +=
 		    length / line6pcm->properties->bytes_per_frame;

 		if (line6pcm->out.pos_done >= runtime->buffer_size)
 			line6pcm->out.pos_done -= runtime->buffer_size;
 	}

 	clear_bit(index, &line6pcm->out.active_urbs);

 	for (i = 0; i < LINE6_ISO_PACKETS; i++)
 		if (urb->iso_frame_desc[i].status == -EXDEV) {
 			shutdown = 1;
 			break;
 		}

 	if (test_and_clear_bit(index, &line6pcm->out.unlink_urbs))
 		shutdown = 1;

 	if (!shutdown) {
 		submit_audio_out_urb(line6pcm);

 		if (test_bit(LINE6_STREAM_PCM, &line6pcm->out.running)) {
 			line6pcm->out.bytes += length;
 			if (line6pcm->out.bytes >= line6pcm->out.period) {
 				line6pcm->out.bytes %= line6pcm->out.period;
 				spin_unlock(&line6pcm->out.lock);
 				snd_pcm_period_elapsed(substream);
 				spin_lock(&line6pcm->out.lock);
 			}
 		}
 	}
 	spin_unlock_irqrestore(&line6pcm->out.lock, flags);
 }

 /* open playback callback */
 static int snd_line6_playback_open(struct snd_pcm_substream *substream)
 {
 	int err;
 	struct snd_pcm_runtime *runtime = substream->runtime;
 	struct snd_line6_pcm *line6pcm = snd_pcm_substream_chip(substream);

 	err = snd_pcm_hw_constraint_ratdens(runtime, 0, SNDRV_PCM_HW_PARAM_RATE,
 					    &line6pcm->properties->rates);
 	if (err < 0)
 		return err;

 	runtime->hw = line6pcm->properties->playback_hw;
 	return 0;
 }

 /* close playback callback */
 static int snd_line6_playback_close(struct snd_pcm_substream *substream)
 {
 	return 0;
 }

 /* playback operators */
 struct snd_pcm_ops snd_line6_playback_ops = {
 	.open = snd_line6_playback_open,
 	.close = snd_line6_playback_close,
 	.ioctl = snd_pcm_lib_ioctl,
 	.hw_params = snd_line6_hw_params,
 	.hw_free = snd_line6_hw_free,
 	.prepare = snd_line6_prepare,
 	.trigger = snd_line6_trigger,
 	.pointer = snd_line6_pointer,
 };

 int line6_create_audio_out_urbs(struct snd_line6_pcm *line6pcm)
 {
 	struct usb_line6 *line6 = line6pcm->line6;
 	int i;

 	/* create audio URBs and fill in constant values: */
 	for (i = 0; i < LINE6_ISO_BUFFERS; ++i) {
 		struct urb *urb;

 		/* URB for audio out: */
 		urb = line6pcm->out.urbs[i] =
 		    usb_alloc_urb(LINE6_ISO_PACKETS, GFP_KERNEL);

 		if (urb == NULL)
 			return -ENOMEM;

 		urb->dev = line6->usbdev;
 		urb->pipe =
 		    usb_sndisocpipe(line6->usbdev,
 				    line6->properties->ep_audio_w &
 				    USB_ENDPOINT_NUMBER_MASK);
 		urb->transfer_flags = URB_ISO_ASAP;
 		urb->start_frame = -1;
 		urb->number_of_packets = LINE6_ISO_PACKETS;
 		urb->interval = LINE6_ISO_INTERVAL;
 		urb->error_count = 0;
 		urb->complete = audio_out_callback;
 	}

 	return 0;
 }
	/*
	* Line 6 Linux USB driver
	*
	* Copyright (C) 2004-2010 Markus Grabner (grabner@icg.tugraz.at)
	*
	* This program is free software; you can redistribute it and/or
	* modify it under the terms of the GNU General Public License as
	* published by the Free Software Foundation, version 2.
	*
	*/

	#include <linux/slab.h>
	#include <sound/core.h>
	#include <sound/pcm.h>
	#include <sound/pcm_params.h>

	#include "capture.h"
	#include "driver.h"
	#include "pcm.h"
	#include "playback.h"

	/*
	Software stereo volume control.
	*/
	static void change_volume(struct urb *urb_out, int volume[],
	int bytes_per_frame)
	{
	int chn = 0;

	if (volume[0] == 256 && volume[1] == 256)
	return; /* maximum volume - no change */

	if (bytes_per_frame == 4) {
	__le16 p, buf_end;

	p = (__le16 *)urb_out->transfer_buffer;
	buf_end = p + urb_out->transfer_buffer_length / sizeof(*p);

	for (; p < buf_end; ++p) {
	short pv = le16_to_cpu(*p);
	int val = (pv * volume[chn & 1]) >> 8;
	pv = clamp(val, -0x8000, 0x7fff);
	*p = cpu_to_le16(pv);
	++chn;
	}
	} else if (bytes_per_frame == 6) {
	unsigned char p, buf_end;

	p = (unsigned char *)urb_out->transfer_buffer;
	buf_end = p + urb_out->transfer_buffer_length;

	for (; p < buf_end; p += 3) {
	int val;

	val = p[0] + (p[1] << 8) + ((signed char)p[2] << 16);
	val = (val * volume[chn & 1]) >> 8;
	val = clamp(val, -0x800000, 0x7fffff);
	p[0] = val;
	p[1] = val >> 8;
	p[2] = val >> 16;
	++chn;
	}
	}
	}

	/*
	Create signal for impulse response test.
	*/
	static void create_impulse_test_signal(struct snd_line6_pcm *line6pcm,
	struct urb *urb_out, int bytes_per_frame)
	{
	int frames = urb_out->transfer_buffer_length / bytes_per_frame;

	if (bytes_per_frame == 4) {
	int i;
	short pi = (short )line6pcm->prev_fbuf;
	short po = (short )urb_out->transfer_buffer;

	for (i = 0; i < frames; ++i) {
	po[0] = pi[0];
	po[1] = 0;
	pi += 2;
	po += 2;
	}
	} else if (bytes_per_frame == 6) {
	int i, j;
	unsigned char *pi = line6pcm->prev_fbuf;
	unsigned char *po = urb_out->transfer_buffer;

	for (i = 0; i < frames; ++i) {
	for (j = 0; j < bytes_per_frame / 2; ++j)
	po[j] = pi[j];

	for (; j < bytes_per_frame; ++j)
	po[j] = 0;

	pi += bytes_per_frame;
	po += bytes_per_frame;
	}
	}
	if (--line6pcm->impulse_count <= 0) {
	((unsigned char *)(urb_out->transfer_buffer))[bytes_per_frame -
	1] =
	line6pcm->impulse_volume;
	line6pcm->impulse_count = line6pcm->impulse_period;
	}
	}

	/*
	Add signal to buffer for software monitoring.
	*/
	static void add_monitor_signal(struct urb urb_out, unsigned char signal,
	int volume, int bytes_per_frame)
	{
	if (volume == 0)
	return; /* zero volume - no change */

	if (bytes_per_frame == 4) {
	__le16 pi, po, *buf_end;

	pi = (__le16 *)signal;
	po = (__le16 *)urb_out->transfer_buffer;
	buf_end = po + urb_out->transfer_buffer_length / sizeof(*po);

	for (; po < buf_end; ++pi, ++po) {
	short pov = le16_to_cpu(*po);
	short piv = le16_to_cpu(*pi);
	int val = pov + ((piv * volume) >> 8);
	pov = clamp(val, -0x8000, 0x7fff);
	*po = cpu_to_le16(pov);
	}
	}

	/*
	We don't need to handle devices with 6 bytes per frame here
	since they all support hardware monitoring.
	*/
	}

	/*
	Find a free URB, prepare audio data, and submit URB.
	must be called in line6pcm->out.lock context
	*/
	static int submit_audio_out_urb(struct snd_line6_pcm *line6pcm)
	{
	int index;
	int i, urb_size, urb_frames;
	int ret;
	const int bytes_per_frame = line6pcm->properties->bytes_per_frame;
	const int frame_increment =
	line6pcm->properties->rates.rats[0].num_min;
	const int frame_factor =
	line6pcm->properties->rates.rats[0].den *
	(USB_INTERVALS_PER_SECOND / LINE6_ISO_INTERVAL);
	struct urb *urb_out;

	index =
	find_first_zero_bit(&line6pcm->out.active_urbs, LINE6_ISO_BUFFERS);

	if (index < 0 \|\| index >= LINE6_ISO_BUFFERS) {
	dev_err(line6pcm->line6->ifcdev, "no free URB found\n");
	return -EINVAL;
	}

	urb_out = line6pcm->out.urbs[index];
	urb_size = 0;

	for (i = 0; i < LINE6_ISO_PACKETS; ++i) {
	/* compute frame size for given sampling rate */
	int fsize = 0;
	struct usb_iso_packet_descriptor *fout =
	&urb_out->iso_frame_desc[i];

	fsize = line6pcm->prev_fsize;
	if (fsize == 0) {
	int n;

	line6pcm->out.count += frame_increment;
	n = line6pcm->out.count / frame_factor;
	line6pcm->out.count -= n * frame_factor;
	fsize = n * bytes_per_frame;
	}

	fout->offset = urb_size;
	fout->length = fsize;
	urb_size += fsize;
	}

	if (urb_size == 0) {
	/* can't determine URB size */
	dev_err(line6pcm->line6->ifcdev, "driver bug: urb_size = 0\n");
	return -EINVAL;
	}

	urb_frames = urb_size / bytes_per_frame;
	urb_out->transfer_buffer =
	line6pcm->out.buffer +
	index * LINE6_ISO_PACKETS * line6pcm->max_packet_size;
	urb_out->transfer_buffer_length = urb_size;
	urb_out->context = line6pcm;

	if (test_bit(LINE6_STREAM_PCM, &line6pcm->out.running) &&
	!test_bit(LINE6_FLAG_PAUSE_PLAYBACK, &line6pcm->flags)) {
	struct snd_pcm_runtime *runtime =
	get_substream(line6pcm, SNDRV_PCM_STREAM_PLAYBACK)->runtime;

	if (line6pcm->out.pos + urb_frames > runtime->buffer_size) {
	/*
	The transferred area goes over buffer boundary,
	copy the data to the temp buffer.
	*/
	int len;

	len = runtime->buffer_size - line6pcm->out.pos;

	if (len > 0) {
	memcpy(urb_out->transfer_buffer,
	runtime->dma_area +
	line6pcm->out.pos * bytes_per_frame,
	len * bytes_per_frame);
	memcpy(urb_out->transfer_buffer +
	len * bytes_per_frame, runtime->dma_area,
	(urb_frames - len) * bytes_per_frame);
	} else
	dev_err(line6pcm->line6->ifcdev, "driver bug: len = %d\n",
	len);
	} else {
	memcpy(urb_out->transfer_buffer,
	runtime->dma_area +
	line6pcm->out.pos * bytes_per_frame,
	urb_out->transfer_buffer_length);
	}

	line6pcm->out.pos += urb_frames;
	if (line6pcm->out.pos >= runtime->buffer_size)
	line6pcm->out.pos -= runtime->buffer_size;

	change_volume(urb_out, line6pcm->volume_playback,
	bytes_per_frame);
	} else {
	memset(urb_out->transfer_buffer, 0,
	urb_out->transfer_buffer_length);
	}

	spin_lock_nested(&line6pcm->in.lock, SINGLE_DEPTH_NESTING);
	if (line6pcm->prev_fbuf) {
	if (test_bit(LINE6_STREAM_IMPULSE, &line6pcm->out.running)) {
	create_impulse_test_signal(line6pcm, urb_out,
	bytes_per_frame);
	if (test_bit(LINE6_STREAM_PCM, &line6pcm->in.running)) {
	line6_capture_copy(line6pcm,
	urb_out->transfer_buffer,
	urb_out->
	transfer_buffer_length);
	line6_capture_check_period(line6pcm,
	urb_out->transfer_buffer_length);
	}
	} else {
	if (!(line6pcm->line6->properties->capabilities & LINE6_CAP_HWMON)
	&& line6pcm->out.running && line6pcm->in.running)
	add_monitor_signal(urb_out, line6pcm->prev_fbuf,
	line6pcm->volume_monitor,
	bytes_per_frame);
	}
	line6pcm->prev_fbuf = NULL;
	line6pcm->prev_fsize = 0;
	}
	spin_unlock(&line6pcm->in.lock);

	ret = usb_submit_urb(urb_out, GFP_ATOMIC);

	if (ret == 0)
	set_bit(index, &line6pcm->out.active_urbs);
	else
	dev_err(line6pcm->line6->ifcdev,
	"URB out #%d submission failed (%d)\n", index, ret);

	return 0;
	}

	/*
	Submit all currently available playback URBs.
	must be called in line6pcm->out.lock context
	*/
	int line6_submit_audio_out_all_urbs(struct snd_line6_pcm *line6pcm)
	{
	int ret = 0, i;

	for (i = 0; i < LINE6_ISO_BUFFERS; ++i) {
	ret = submit_audio_out_urb(line6pcm);
	if (ret < 0)
	break;
	}

	return ret;
	}

	/*
	Callback for completed playback URB.
	*/
	static void audio_out_callback(struct urb *urb)
	{
	int i, index, length = 0, shutdown = 0;
	unsigned long flags;
	struct snd_line6_pcm line6pcm = (struct snd_line6_pcm )urb->context;
	struct snd_pcm_substream *substream =
	get_substream(line6pcm, SNDRV_PCM_STREAM_PLAYBACK);

	#if USE_CLEAR_BUFFER_WORKAROUND
	memset(urb->transfer_buffer, 0, urb->transfer_buffer_length);
	#endif

	line6pcm->out.last_frame = urb->start_frame;

	/* find index of URB */
	for (index = 0; index < LINE6_ISO_BUFFERS; index++)
	if (urb == line6pcm->out.urbs[index])
	break;

	if (index >= LINE6_ISO_BUFFERS)
	return; /* URB has been unlinked asynchronously */

	for (i = 0; i < LINE6_ISO_PACKETS; i++)
	length += urb->iso_frame_desc[i].length;

	spin_lock_irqsave(&line6pcm->out.lock, flags);

	if (test_bit(LINE6_STREAM_PCM, &line6pcm->out.running)) {
	struct snd_pcm_runtime *runtime = substream->runtime;

	line6pcm->out.pos_done +=
	length / line6pcm->properties->bytes_per_frame;

	if (line6pcm->out.pos_done >= runtime->buffer_size)
	line6pcm->out.pos_done -= runtime->buffer_size;
	}

	clear_bit(index, &line6pcm->out.active_urbs);

	for (i = 0; i < LINE6_ISO_PACKETS; i++)
	if (urb->iso_frame_desc[i].status == -EXDEV) {
	shutdown = 1;
	break;
	}

	if (test_and_clear_bit(index, &line6pcm->out.unlink_urbs))
	shutdown = 1;

	if (!shutdown) {
	submit_audio_out_urb(line6pcm);

	if (test_bit(LINE6_STREAM_PCM, &line6pcm->out.running)) {
	line6pcm->out.bytes += length;
	if (line6pcm->out.bytes >= line6pcm->out.period) {
	line6pcm->out.bytes %= line6pcm->out.period;
	spin_unlock(&line6pcm->out.lock);
	snd_pcm_period_elapsed(substream);
	spin_lock(&line6pcm->out.lock);
	}
	}
	}
	spin_unlock_irqrestore(&line6pcm->out.lock, flags);
	}

	/* open playback callback */
	static int snd_line6_playback_open(struct snd_pcm_substream *substream)
	{
	int err;
	struct snd_pcm_runtime *runtime = substream->runtime;
	struct snd_line6_pcm *line6pcm = snd_pcm_substream_chip(substream);

	err = snd_pcm_hw_constraint_ratdens(runtime, 0, SNDRV_PCM_HW_PARAM_RATE,
	&line6pcm->properties->rates);
	if (err < 0)
	return err;

	runtime->hw = line6pcm->properties->playback_hw;
	return 0;
	}

	/* close playback callback */
	static int snd_line6_playback_close(struct snd_pcm_substream *substream)
	{
	return 0;
	}

	/* playback operators */
	struct snd_pcm_ops snd_line6_playback_ops = {
	.open = snd_line6_playback_open,
	.close = snd_line6_playback_close,
	.ioctl = snd_pcm_lib_ioctl,
	.hw_params = snd_line6_hw_params,
	.hw_free = snd_line6_hw_free,
	.prepare = snd_line6_prepare,
	.trigger = snd_line6_trigger,
	.pointer = snd_line6_pointer,
	};

	int line6_create_audio_out_urbs(struct snd_line6_pcm *line6pcm)
	{
	struct usb_line6 *line6 = line6pcm->line6;
	int i;

	/* create audio URBs and fill in constant values: */
	for (i = 0; i < LINE6_ISO_BUFFERS; ++i) {
	struct urb *urb;

	/* URB for audio out: */
	urb = line6pcm->out.urbs[i] =
	usb_alloc_urb(LINE6_ISO_PACKETS, GFP_KERNEL);

	if (urb == NULL)
	return -ENOMEM;

	urb->dev = line6->usbdev;
	urb->pipe =
	usb_sndisocpipe(line6->usbdev,
	line6->properties->ep_audio_w &
	USB_ENDPOINT_NUMBER_MASK);
	urb->transfer_flags = URB_ISO_ASAP;
	urb->start_frame = -1;
	urb->number_of_packets = LINE6_ISO_PACKETS;
	urb->interval = LINE6_ISO_INTERVAL;
	urb->error_count = 0;
	urb->complete = audio_out_callback;
	}

	return 0;
	}