Add working loopback implementation, helper scripts

Reworked the original aloop implementation to have the PCM devices loop on themselves, and subscribe the the AVIRT system.

Signed-off-by: Mark Farrugia <mark.farrugia@fiberdyne.com.au>

5 files changed, 1013 insertions, 185 deletions

diff --git a/loopback/Makefile b/loopback/Makefile
index 55da206..0464aba 100644
--- a/loopback/Makefile
+++ b/loopback/Makefile
@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0
 obj-$(CONFIG_AVIRT_LOOPBACKAP) += avirt_loopbackap.o
 
 $(info $(src))
diff --git a/loopback/loopback.c b/loopback/loopback.c
index e9c4bcb..2e02711 100644
--- a/loopback/loopback.c
+++ b/loopback/loopback.c
@@ -1,308 +1,1125 @@
-// SPDX-License-Identifier: GPL-2.0
 /*
- * ALSA Virtual Soundcard
+ *  Loopback soundcard
  *
- * loopback_audiopath.c - AVIRT sample Audio Path definition
+ *  Original code:
+ *  Copyright (c) by Jaroslav Kysela <perex@perex.cz>
+ *
+ *  More accurate positioning and full-duplex support:
+ *  Copyright (c) Ahmet İnan <ainan at mathematik.uni-freiburg.de>
+ *
+ *  Major (almost complete) rewrite:
+ *  Copyright (c) by Takashi Iwai <tiwai@suse.de>
+ *
+ *  A next major update in 2010 (separate timers for playback and capture):
+ *  Copyright (c) Jaroslav Kysela <perex@perex.cz>
+ * 
+ *  Adapt to use AVIRT, looping is now conducted on the same device
+ *  Copyright (c) by Mark Farrugia <mark.farrugia@fiberdyne.com.au>
+ *
+ *   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; either version 2 of the License, or
+ *   (at your option) any later version.
+ *
+ *   This program is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *   GNU General Public License for more details.
+ *
+ *   You should have received a copy of the GNU General Public License
+ *   along with this program; if not, write to the Free Software
+ *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
  *
- * Copyright (C) 2010-2018 Fiberdyne Systems Pty Ltd
  */
 
-#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/jiffies.h>
 #include <linux/slab.h>
+#include <linux/time.h>
+#include <linux/wait.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <sound/core.h>
+#include <sound/control.h>
+#include <sound/pcm.h>
+#include <sound/pcm_params.h>
+#include <sound/info.h>
+#include <sound/initval.h>
 #include <avirt/core.h>
 
-MODULE_AUTHOR("JOSHANNE <james.oshannessy@fiberdyne.com.au>");
-MODULE_AUTHOR("MFARRUGI <mark.farrugia@fiberdyne.com.au>");
-MODULE_DESCRIPTION("Sample Audio Path Module Interface");
-MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Jaroslav Kysela <perex@perex.cz>");
+MODULE_DESCRIPTION("A loopback soundcard");
+MODULE_LICENSE("GPL");
+MODULE_SUPPORTED_DEVICE("{{ALSA,Loopback soundcard}}");
+
+#define AP_UID "ap_loopback"
 
-#define AP_LOGNAME "LOOPAP"
+#define AP_INFOK(fmt, args...) DINFO(AP_UID, fmt, ##args)
+#define AP_PRINTK(fmt, args...) DDEBUG(AP_UID, fmt, ##args)
+#define AP_ERRORK(fmt, args...) DERROR(AP_UID, fmt, ##args)
 
-#define AP_INFOK(fmt, args...) DINFO(AP_LOGNAME, fmt, ##args)
-#define AP_PRINTK(fmt, args...) DPRINT(AP_LOGNAME, fmt, ##args)
-#define AP_ERRORK(fmt, args...) DERROR(AP_LOGNAME, fmt, ##args)
+#define NO_PITCH 100000
 
 static struct avirt_coreinfo *coreinfo;
+static struct loopback *loopback;
+
+struct loopback_pcm;
+
+struct loopback_cable {
+	spinlock_t lock;
+	struct loopback_pcm *streams[2];
+	struct snd_pcm_hardware hw;
+	/* flags */
+	unsigned int valid;
+	unsigned int running;
+	unsigned int pause;
+};
+
+struct loopback_setup {
+	unsigned int notify : 1;
+	unsigned int rate_shift;
+	unsigned int format;
+	unsigned int rate;
+	unsigned int channels;
+	struct snd_ctl_elem_id active_id;
+	struct snd_ctl_elem_id format_id;
+	struct snd_ctl_elem_id rate_id;
+	struct snd_ctl_elem_id channels_id;
+};
+
+struct loopback {
+	struct snd_card *card;
+	struct mutex cable_lock;
+	struct loopback_cable *cables[MAX_STREAMS];
+	struct snd_pcm *pcm[MAX_STREAMS];
+	struct loopback_setup setup[MAX_STREAMS];
+};
 
 struct loopback_pcm {
+	struct loopback *loopback;
 	struct snd_pcm_substream *substream;
-	spinlock_t lock;
+	struct loopback_cable *cable;
+	unsigned int pcm_buffer_size;
+	unsigned int buf_pos; /* position in buffer */
+	unsigned int silent_size;
+	/* PCM parameters */
+	unsigned int pcm_period_size;
+	unsigned int pcm_bps; /* bytes per second */
+	unsigned int pcm_salign; /* bytes per sample * channels */
+	unsigned int pcm_rate_shift; /* rate shift value */
+	/* flags */
+	unsigned int period_update_pending : 1;
+	/* timer stuff */
+	unsigned int irq_pos; /* fractional IRQ position */
+	unsigned int period_size_frac;
+	unsigned int last_drift;
+	unsigned long last_jiffies;
 	struct timer_list timer;
-	unsigned long base_time;
-	unsigned int frac_pos; /* fractional sample position (based HZ) */
-	unsigned int frac_period_rest;
-	unsigned int frac_buffer_size; /* buffer_size * HZ */
-	unsigned int frac_period_size; /* period_size * HZ */
-	unsigned int rate;
-	int elapsed;
 };
 
-int systimer_create(struct snd_pcm_substream *substream);
-void systimer_free(struct snd_pcm_substream *substream);
-int systimer_start(struct snd_pcm_substream *substream);
-int systimer_stop(struct snd_pcm_substream *substream);
-snd_pcm_uframes_t systimer_pointer(struct snd_pcm_substream *substream);
-int systimer_prepare(struct snd_pcm_substream *substream);
-void systimer_rearm(struct loopback_pcm *dpcm);
-void systimer_update(struct loopback_pcm *dpcm);
+static inline unsigned int byte_pos(struct loopback_pcm *dpcm, unsigned int x)
+{
+	if (dpcm->pcm_rate_shift == NO_PITCH) {
+		x /= HZ;
+	} else {
+		x = div_u64(NO_PITCH * (unsigned long long)x,
+			    HZ * (unsigned long long)dpcm->pcm_rate_shift);
+	}
+	return x - (x % dpcm->pcm_salign);
+}
 
-void loopback_callback(struct timer_list *tlist);
+static inline unsigned int frac_pos(struct loopback_pcm *dpcm, unsigned int x)
+{
+	if (dpcm->pcm_rate_shift == NO_PITCH) { /* no pitch */
+		return x * HZ;
+	} else {
+		x = div_u64(dpcm->pcm_rate_shift * (unsigned long long)x * HZ,
+			    NO_PITCH);
+	}
+	return x;
+}
 
-/********************************
- * Loopback Timer Functions
- ********************************/
+static inline struct loopback_setup *get_setup(struct loopback_pcm *dpcm)
+{
+	return &dpcm->loopback->setup[dpcm->substream->pcm->device];
+}
 
-int systimer_create(struct snd_pcm_substream *substream)
+static inline unsigned int get_notify(struct loopback_pcm *dpcm)
 {
-	struct snd_pcm_runtime *runtime = substream->runtime;
+	return get_setup(dpcm)->notify;
+}
 
-	struct loopback_pcm *dpcm;
-	dpcm = kzalloc(sizeof(*dpcm), GFP_KERNEL);
-	if (!dpcm)
-		return -ENOMEM;
+static inline unsigned int get_rate_shift(struct loopback_pcm *dpcm)
+{
+	return get_setup(dpcm)->rate_shift;
+}
 
-	timer_setup(&dpcm->timer, loopback_callback, 0);
-	spin_lock_init(&dpcm->lock);
-	dpcm->substream = substream;
+/* call in cable->lock */
+static void loopback_timer_start(struct loopback_pcm *dpcm)
+{
+	unsigned long tick;
+	unsigned int rate_shift = get_rate_shift(dpcm);
 
-	runtime->private_data = dpcm;
-	return 0;
+	if (rate_shift != dpcm->pcm_rate_shift) {
+		dpcm->pcm_rate_shift = rate_shift;
+		dpcm->period_size_frac = frac_pos(dpcm, dpcm->pcm_period_size);
+	}
+	if (dpcm->period_size_frac <= dpcm->irq_pos) {
+		dpcm->irq_pos %= dpcm->period_size_frac;
+		dpcm->period_update_pending = 1;
+	}
+	tick = dpcm->period_size_frac - dpcm->irq_pos;
+	tick = (tick + dpcm->pcm_bps - 1) / dpcm->pcm_bps;
+	mod_timer(&dpcm->timer, jiffies + tick);
 }
 
-void systimer_free(struct snd_pcm_substream *substream)
+/* call in cable->lock */
+static inline void loopback_timer_stop(struct loopback_pcm *dpcm)
 {
-	struct snd_pcm_runtime *runtime = substream->runtime;
-	kfree(runtime->private_data);
+	del_timer(&dpcm->timer);
+	dpcm->timer.expires = 0;
 }
 
-int systimer_start(struct snd_pcm_substream *substream)
+static inline void loopback_timer_stop_sync(struct loopback_pcm *dpcm)
 {
-	struct snd_pcm_runtime *runtime = substream->runtime;
-	struct loopback_pcm *dpcm = runtime->private_data;
-	spin_lock(&dpcm->lock);
-	dpcm->base_time = jiffies;
-	systimer_rearm(dpcm);
-	spin_unlock(&dpcm->lock);
+	del_timer_sync(&dpcm->timer);
+}
+
+#define CABLE_VALID_PLAYBACK (1 << SNDRV_PCM_STREAM_PLAYBACK)
+#define CABLE_VALID_CAPTURE (1 << SNDRV_PCM_STREAM_CAPTURE)
+#define CABLE_VALID_BOTH (CABLE_VALID_PLAYBACK | CABLE_VALID_CAPTURE)
+
+static int loopback_check_format(struct loopback_cable *cable, int stream)
+{
+	struct snd_pcm_runtime *runtime, *cruntime;
+	struct loopback_setup *setup;
+	struct snd_card *card;
+	int check;
+
+	if (cable->valid != CABLE_VALID_BOTH) {
+		if (stream == SNDRV_PCM_STREAM_PLAYBACK)
+			goto __notify;
+		return 0;
+	}
+	runtime = cable->streams[SNDRV_PCM_STREAM_PLAYBACK]->substream->runtime;
+	cruntime = cable->streams[SNDRV_PCM_STREAM_CAPTURE]->substream->runtime;
+	check = runtime->format != cruntime->format ||
+		runtime->rate != cruntime->rate ||
+		runtime->channels != cruntime->channels;
+	if (!check)
+		return 0;
+	if (stream == SNDRV_PCM_STREAM_CAPTURE) {
+		return -EIO;
+	} else {
+		snd_pcm_stop(
+			cable->streams[SNDRV_PCM_STREAM_CAPTURE]->substream,
+			SNDRV_PCM_STATE_DRAINING);
+	__notify:
+		runtime = cable->streams[SNDRV_PCM_STREAM_PLAYBACK]
+				  ->substream->runtime;
+		setup = get_setup(cable->streams[SNDRV_PCM_STREAM_PLAYBACK]);
+		card = cable->streams[SNDRV_PCM_STREAM_PLAYBACK]->loopback->card;
+		if (setup->format != runtime->format) {
+			snd_ctl_notify(card, SNDRV_CTL_EVENT_MASK_VALUE,
+				       &setup->format_id);
+			setup->format = runtime->format;
+		}
+		if (setup->rate != runtime->rate) {
+			snd_ctl_notify(card, SNDRV_CTL_EVENT_MASK_VALUE,
+				       &setup->rate_id);
+			setup->rate = runtime->rate;
+		}
+		if (setup->channels != runtime->channels) {
+			snd_ctl_notify(card, SNDRV_CTL_EVENT_MASK_VALUE,
+				       &setup->channels_id);
+			setup->channels = runtime->channels;
+		}
+	}
 	return 0;
 }
 
-int systimer_stop(struct snd_pcm_substream *substream)
+static void loopback_active_notify(struct loopback_pcm *dpcm)
+{
+	snd_ctl_notify(dpcm->loopback->card, SNDRV_CTL_EVENT_MASK_VALUE,
+		       &get_setup(dpcm)->active_id);
+}
+
+static int loopback_trigger(struct snd_pcm_substream *substream, int cmd)
 {
 	struct snd_pcm_runtime *runtime = substream->runtime;
 	struct loopback_pcm *dpcm = runtime->private_data;
-	spin_lock(&dpcm->lock);
-	del_timer(&dpcm->timer);
-	spin_unlock(&dpcm->lock);
+	struct loopback_cable *cable = dpcm->cable;
+	int err, stream = 1 << substream->stream;
+
+	AP_INFOK();
+
+	switch (cmd) {
+	case SNDRV_PCM_TRIGGER_START:
+		err = loopback_check_format(cable, substream->stream);
+		if (err < 0)
+			return err;
+		dpcm->last_jiffies = jiffies;
+		dpcm->pcm_rate_shift = 0;
+		dpcm->last_drift = 0;
+		spin_lock(&cable->lock);
+		cable->running |= stream;
+		cable->pause &= ~stream;
+		loopback_timer_start(dpcm);
+		spin_unlock(&cable->lock);
+		if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
+			loopback_active_notify(dpcm);
+		break;
+	case SNDRV_PCM_TRIGGER_STOP:
+		spin_lock(&cable->lock);
+		cable->running &= ~stream;
+		cable->pause &= ~stream;
+		loopback_timer_stop(dpcm);
+		spin_unlock(&cable->lock);
+		if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
+			loopback_active_notify(dpcm);
+		break;
+	case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
+	case SNDRV_PCM_TRIGGER_SUSPEND:
+		spin_lock(&cable->lock);
+		cable->pause |= stream;
+		loopback_timer_stop(dpcm);
+		spin_unlock(&cable->lock);
+		if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
+			loopback_active_notify(dpcm);
+		break;
+	case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
+	case SNDRV_PCM_TRIGGER_RESUME:
+		spin_lock(&cable->lock);
+		dpcm->last_jiffies = jiffies;
+		cable->pause &= ~stream;
+		loopback_timer_start(dpcm);
+		spin_unlock(&cable->lock);
+		if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
+			loopback_active_notify(dpcm);
+		break;
+	default:
+		return -EINVAL;
+	}
 	return 0;
 }
 
-snd_pcm_uframes_t systimer_pointer(struct snd_pcm_substream *substream)
+static void params_change(struct snd_pcm_substream *substream)
 {
 	struct snd_pcm_runtime *runtime = substream->runtime;
 	struct loopback_pcm *dpcm = runtime->private_data;
+	struct loopback_cable *cable = dpcm->cable;
 
-	snd_pcm_uframes_t pos;
-
-	spin_lock(&dpcm->lock);
-	systimer_update(dpcm);
-	pos = dpcm->frac_pos / HZ;
-	spin_unlock(&dpcm->lock);
-	return pos;
+	cable->hw.formats = pcm_format_to_bits(runtime->format);
+	cable->hw.rate_min = runtime->rate;
+	cable->hw.rate_max = runtime->rate;
+	cable->hw.channels_min = runtime->channels;
+	cable->hw.channels_max = runtime->channels;
 }
 
-int systimer_prepare(struct snd_pcm_substream *substream)
+static int loopback_prepare(struct snd_pcm_substream *substream)
 {
 	struct snd_pcm_runtime *runtime = substream->runtime;
 	struct loopback_pcm *dpcm = runtime->private_data;
+	struct loopback_cable *cable = dpcm->cable;
+	int bps, salign;
 
-	dpcm->frac_pos = 0;
-	dpcm->rate = runtime->rate;
-	dpcm->frac_buffer_size = runtime->buffer_size * HZ;
-	dpcm->frac_period_size = runtime->period_size * HZ;
-	dpcm->frac_period_rest = dpcm->frac_period_size;
-	dpcm->elapsed = 0;
+	loopback_timer_stop_sync(dpcm);
+
+	salign =
+		(snd_pcm_format_width(runtime->format) * runtime->channels) / 8;
+	bps = salign * runtime->rate;
+	if (bps <= 0 || salign <= 0)
+		return -EINVAL;
+
+	dpcm->buf_pos = 0;
+	dpcm->pcm_buffer_size = frames_to_bytes(runtime, runtime->buffer_size);
+	if (substream->stream == SNDRV_PCM_STREAM_CAPTURE) {
+		/* clear capture buffer */
+		dpcm->silent_size = dpcm->pcm_buffer_size;
+		snd_pcm_format_set_silence(runtime->format, runtime->dma_area,
+					   runtime->buffer_size *
+						   runtime->channels);
+	}
+
+	dpcm->irq_pos = 0;
+	dpcm->period_update_pending = 0;
+	dpcm->pcm_bps = bps;
+	dpcm->pcm_salign = salign;
+	dpcm->pcm_period_size = frames_to_bytes(runtime, runtime->period_size);
+
+	mutex_lock(&dpcm->loopback->cable_lock);
+	if (!(cable->valid & ~(1 << substream->stream)) ||
+	    (get_setup(dpcm)->notify &&
+	     substream->stream == SNDRV_PCM_STREAM_PLAYBACK))
+		params_change(substream);
+	cable->valid |= 1 << substream->stream;
+	mutex_unlock(&dpcm->loopback->cable_lock);
 
 	return 0;
 }
 
-void systimer_rearm(struct loopback_pcm *dpcm)
+static void clear_capture_buf(struct loopback_pcm *dpcm, unsigned int bytes)
 {
-	mod_timer(&dpcm->timer, jiffies + (dpcm->frac_period_rest + dpcm->rate -
-					   1) / dpcm->rate);
+	struct snd_pcm_runtime *runtime = dpcm->substream->runtime;
+	char *dst = runtime->dma_area;
+	unsigned int dst_off = dpcm->buf_pos;
+
+	if (dpcm->silent_size >= dpcm->pcm_buffer_size)
+		return;
+	if (dpcm->silent_size + bytes > dpcm->pcm_buffer_size)
+		bytes = dpcm->pcm_buffer_size - dpcm->silent_size;
+
+	for (;;) {
+		unsigned int size = bytes;
+		if (dst_off + size > dpcm->pcm_buffer_size)
+			size = dpcm->pcm_buffer_size - dst_off;
+		snd_pcm_format_set_silence(runtime->format, dst + dst_off,
+					   bytes_to_frames(runtime, size) *
+						   runtime->channels);
+		dpcm->silent_size += size;
+		bytes -= size;
+		if (!bytes)
+			break;
+		dst_off = 0;
+	}
 }
 
-void systimer_update(struct loopback_pcm *dpcm)
+static void copy_play_buf(struct loopback_pcm *play, struct loopback_pcm *capt,
+			  unsigned int bytes)
 {
-	unsigned long delta;
+	struct snd_pcm_runtime *runtime = play->substream->runtime;
+	char *src = runtime->dma_area;
+	char *dst = capt->substream->runtime->dma_area;
+	unsigned int src_off = play->buf_pos;
+	unsigned int dst_off = capt->buf_pos;
+	unsigned int clear_bytes = 0;
 
-	delta = jiffies - dpcm->base_time;
-	if (!delta)
-		return;
-	dpcm->base_time += delta;
-	delta *= dpcm->rate;
-	dpcm->frac_pos += delta;
-	while (dpcm->frac_pos >= dpcm->frac_buffer_size)
-		dpcm->frac_pos -= dpcm->frac_buffer_size;
-	while (dpcm->frac_period_rest <= delta) {
-		dpcm->elapsed++;
-		dpcm->frac_period_rest += dpcm->frac_period_size;
+	/* check if playback is draining, trim the capture copy size
+	 * when our pointer is at the end of playback ring buffer */
+	if (runtime->status->state == SNDRV_PCM_STATE_DRAINING &&
+	    snd_pcm_playback_hw_avail(runtime) < runtime->buffer_size) {
+		snd_pcm_uframes_t appl_ptr, appl_ptr1, diff;
+		appl_ptr = appl_ptr1 = runtime->control->appl_ptr;
+		appl_ptr1 -= appl_ptr1 % runtime->buffer_size;
+		appl_ptr1 += play->buf_pos / play->pcm_salign;
+		if (appl_ptr < appl_ptr1)
+			appl_ptr1 -= runtime->buffer_size;
+		diff = (appl_ptr - appl_ptr1) * play->pcm_salign;
+		if (diff < bytes) {
+			clear_bytes = bytes - diff;
+			bytes = diff;
+		}
+	}
+
+	for (;;) {
+		unsigned int size = bytes;
+		if (src_off + size > play->pcm_buffer_size)
+			size = play->pcm_buffer_size - src_off;
+		if (dst_off + size > capt->pcm_buffer_size)
+			size = capt->pcm_buffer_size - dst_off;
+		memcpy(dst + dst_off, src + src_off, size);
+		capt->silent_size = 0;
+		bytes -= size;
+		if (!bytes)
+			break;
+		src_off = (src_off + size) % play->pcm_buffer_size;
+		dst_off = (dst_off + size) % capt->pcm_buffer_size;
+	}
+
+	if (clear_bytes > 0) {
+		clear_capture_buf(capt, clear_bytes);
+		capt->silent_size = 0;
 	}
-	dpcm->frac_period_rest -= delta;
 }
 
-/*******
- * Loopback Timer Callback
- *******/
+static inline unsigned int bytepos_delta(struct loopback_pcm *dpcm,
+					 unsigned int jiffies_delta)
+{
+	unsigned long last_pos;
+	unsigned int delta;
 
-//
-void loopback_callback(struct timer_list *tlist)
+	last_pos = byte_pos(dpcm, dpcm->irq_pos);
+	dpcm->irq_pos += jiffies_delta * dpcm->pcm_bps;
+	delta = byte_pos(dpcm, dpcm->irq_pos) - last_pos;
+	if (delta >= dpcm->last_drift)
+		delta -= dpcm->last_drift;
+	dpcm->last_drift = 0;
+	if (dpcm->irq_pos >= dpcm->period_size_frac) {
+		dpcm->irq_pos %= dpcm->period_size_frac;
+		dpcm->period_update_pending = 1;
+	}
+	return delta;
+}
+
+static inline void bytepos_finish(struct loopback_pcm *dpcm, unsigned int delta)
 {
-	struct loopback_pcm *dpcm = from_timer(dpcm, tlist, timer);
+	dpcm->buf_pos += delta;
+	dpcm->buf_pos %= dpcm->pcm_buffer_size;
+}
 
-	unsigned long flags;
-	int elapsed = 0;
+/* call in cable->lock */
+static unsigned int loopback_pos_update(struct loopback_cable *cable)
+{
+	struct loopback_pcm *dpcm_play =
+		cable->streams[SNDRV_PCM_STREAM_PLAYBACK];
+	struct loopback_pcm *dpcm_capt =
+		cable->streams[SNDRV_PCM_STREAM_CAPTURE];
+	unsigned long delta_play = 0, delta_capt = 0;
+	unsigned int running, count1, count2;
+
+	running = cable->running ^ cable->pause;
+	if (running & (1 << SNDRV_PCM_STREAM_PLAYBACK)) {
+		delta_play = jiffies - dpcm_play->last_jiffies;
+		dpcm_play->last_jiffies += delta_play;
+	}
+
+	if (running & (1 << SNDRV_PCM_STREAM_CAPTURE)) {
+		delta_capt = jiffies - dpcm_capt->last_jiffies;
+		dpcm_capt->last_jiffies += delta_capt;
+	}
 
-	AP_INFOK("");
-	spin_lock_irqsave(&dpcm->lock, flags);
+	if (delta_play == 0 && delta_capt == 0)
+		goto unlock;
 
-	// Perform copy from playback to capture
-	systimer_update(dpcm);
-	systimer_rearm(dpcm);
-	elapsed = dpcm->elapsed;
-	dpcm->elapsed = 0;
+	if (delta_play > delta_capt) {
+		count1 = bytepos_delta(dpcm_play, delta_play - delta_capt);
+		bytepos_finish(dpcm_play, count1);
+		delta_play = delta_capt;
+	} else if (delta_play < delta_capt) {
+		count1 = bytepos_delta(dpcm_capt, delta_capt - delta_play);
+		clear_capture_buf(dpcm_capt, count1);
+		bytepos_finish(dpcm_capt, count1);
+		delta_capt = delta_play;
+	}
+
+	if (delta_play == 0 && delta_capt == 0)
+		goto unlock;
 
-	spin_unlock_irqrestore(&dpcm->lock, flags);
-	if (elapsed)
-		coreinfo->pcm_buff_complete(dpcm->substream);
+	/* note delta_capt == delta_play at this moment */
+	count1 = bytepos_delta(dpcm_play, delta_play);
+	count2 = bytepos_delta(dpcm_capt, delta_capt);
+	if (count1 < count2) {
+		dpcm_capt->last_drift = count2 - count1;
+		count1 = count2;
+	} else if (count1 > count2) {
+		dpcm_play->last_drift = count1 - count2;
+	}
+	copy_play_buf(dpcm_play, dpcm_capt, count1);
+	bytepos_finish(dpcm_play, count1);
+	bytepos_finish(dpcm_capt, count1);
+unlock:
+	return running;
 }
 
-/*******************************************************************************
- * Audio Path ALSA PCM Callbacks
- ******************************************************************************/
-static int loopback_pcm_open(struct snd_pcm_substream *substream)
+static void loopback_timer_function(struct timer_list *t)
 {
-	int err;
+	struct loopback_pcm *dpcm = from_timer(dpcm, t, timer);
+	unsigned long flags;
+
+	spin_lock_irqsave(&dpcm->cable->lock, flags);
+	if (loopback_pos_update(dpcm->cable) & (1 << dpcm->substream->stream)) {
+		loopback_timer_start(dpcm);
+		if (dpcm->period_update_pending) {
+			dpcm->period_update_pending = 0;
+			spin_unlock_irqrestore(&dpcm->cable->lock, flags);
+			/* need to unlock before calling below */
+			avirt_pcm_period_elapsed(dpcm->substream);
+			return;
+		}
+	}
+	spin_unlock_irqrestore(&dpcm->cable->lock, flags);
+}
 
+static snd_pcm_uframes_t loopback_pointer(struct snd_pcm_substream *substream)
+{
 	struct snd_pcm_runtime *runtime = substream->runtime;
 	struct loopback_pcm *dpcm = runtime->private_data;
+	snd_pcm_uframes_t pos;
 
-	err = systimer_create(substream);
-	if (err < 0)
-		return err;
+	spin_lock(&dpcm->cable->lock);
+	loopback_pos_update(dpcm->cable);
+	pos = dpcm->buf_pos;
+	spin_unlock(&dpcm->cable->lock);
+	return bytes_to_frames(runtime, pos);
+}
 
-	return 0;
+static const struct snd_pcm_hardware loopback_pcm_hardware = {
+	.info = (SNDRV_PCM_INFO_INTERLEAVED | SNDRV_PCM_INFO_MMAP |
+		 SNDRV_PCM_INFO_MMAP_VALID | SNDRV_PCM_INFO_PAUSE |
+		 SNDRV_PCM_INFO_RESUME),
+	.formats = (SNDRV_PCM_FMTBIT_S16_LE | SNDRV_PCM_FMTBIT_S16_BE |
+		    SNDRV_PCM_FMTBIT_S32_LE | SNDRV_PCM_FMTBIT_S32_BE |
+		    SNDRV_PCM_FMTBIT_FLOAT_LE | SNDRV_PCM_FMTBIT_FLOAT_BE),
+	.rates = SNDRV_PCM_RATE_CONTINUOUS | SNDRV_PCM_RATE_8000_192000,
+	.rate_min = 8000,
+	.rate_max = 192000,
+	.channels_min = 1,
+	.channels_max = 32,
+	.buffer_bytes_max = 2 * 1024 * 1024,
+	.period_bytes_min = 64,
+	/* note check overflow in frac_pos() using pcm_rate_shift before
+	   changing period_bytes_max value */
+	.period_bytes_max = 1024 * 1024,
+	.periods_min = 1,
+	.periods_max = 1024,
+	.fifo_size = 0,
+};
+
+static void loopback_runtime_free(struct snd_pcm_runtime *runtime)
+{
+	struct loopback_pcm *dpcm = runtime->private_data;
+	kfree(dpcm);
 }
 
-static int loopback_pcm_close(struct snd_pcm_substream *substream)
+static int loopback_hw_free(struct snd_pcm_substream *substream)
 {
 	struct snd_pcm_runtime *runtime = substream->runtime;
 	struct loopback_pcm *dpcm = runtime->private_data;
+	struct loopback_cable *cable = dpcm->cable;
 
-	AP_INFOK("Close");
+	mutex_lock(&dpcm->loopback->cable_lock);
+	cable->valid &= ~(1 << substream->stream);
+	mutex_unlock(&dpcm->loopback->cable_lock);
 
-	systimer_free(substream);
 	return 0;
 }
 
-static snd_pcm_uframes_t
-	loopback_pcm_pointer(struct snd_pcm_substream *substream)
+static int rule_format(struct snd_pcm_hw_params *params,
+		       struct snd_pcm_hw_rule *rule)
 {
-	AP_INFOK("Pointer");
+	struct loopback_pcm *dpcm = rule->private;
+	struct loopback_cable *cable = dpcm->cable;
+	struct snd_mask m;
 
-	return systimer_pointer(substream);
+	snd_mask_none(&m);
+	mutex_lock(&dpcm->loopback->cable_lock);
+	m.bits[0] = (u_int32_t)cable->hw.formats;
+	m.bits[1] = (u_int32_t)(cable->hw.formats >> 32);
+	mutex_unlock(&dpcm->loopback->cable_lock);
+	return snd_mask_refine(hw_param_mask(params, rule->var), &m);
 }
 
-static int loopback_pcm_trigger(struct snd_pcm_substream *substream, int cmd)
+static int rule_rate(struct snd_pcm_hw_params *params,
+		     struct snd_pcm_hw_rule *rule)
 {
-	AP_INFOK("Trigger");
+	struct loopback_pcm *dpcm = rule->private;
+	struct loopback_cable *cable = dpcm->cable;
+	struct snd_interval t;
 
-	switch (cmd) {
-	case SNDRV_PCM_TRIGGER_START:
-	case SNDRV_PCM_TRIGGER_RESUME:
-		return systimer_start(substream);
-	case SNDRV_PCM_TRIGGER_STOP:
-	case SNDRV_PCM_TRIGGER_SUSPEND:
-		return systimer_stop(substream);
+	mutex_lock(&dpcm->loopback->cable_lock);
+	t.min = cable->hw.rate_min;
+	t.max = cable->hw.rate_max;
+	mutex_unlock(&dpcm->loopback->cable_lock);
+	t.openmin = t.openmax = 0;
+	t.integer = 0;
+	return snd_interval_refine(hw_param_interval(params, rule->var), &t);
+}
+
+static int rule_channels(struct snd_pcm_hw_params *params,
+			 struct snd_pcm_hw_rule *rule)
+{
+	struct loopback_pcm *dpcm = rule->private;
+	struct loopback_cable *cable = dpcm->cable;
+	struct snd_interval t;
+
+	mutex_lock(&dpcm->loopback->cable_lock);
+	t.min = cable->hw.channels_min;
+	t.max = cable->hw.channels_max;
+	mutex_unlock(&dpcm->loopback->cable_lock);
+	t.openmin = t.openmax = 0;
+	t.integer = 0;
+	return snd_interval_refine(hw_param_interval(params, rule->var), &t);
+}
+
+static void free_cable(struct snd_pcm_substream *substream)
+{
+	struct loopback_cable *cable;
+
+	cable = loopback->cables[substream->pcm->device];
+	if (!cable)
+		return;
+	if (cable->streams[!substream->stream]) {
+		/* other stream is still alive */
+		spin_lock_irq(&cable->lock);
+		cable->streams[substream->stream] = NULL;
+		spin_unlock_irq(&cable->lock);
+	} else {
+		/* free the cable */
+		loopback->cables[substream->pcm->device] = NULL;
+		kfree(cable);
 	}
-	return -EINVAL;
 }
 
-static int loopback_pcm_prepare(struct snd_pcm_substream *substream)
+static int loopback_open(struct snd_pcm_substream *substream)
 {
 	struct snd_pcm_runtime *runtime = substream->runtime;
-	struct loopback_pcm *dpcm = runtime->private_data;
+	struct loopback_pcm *dpcm;
+	struct loopback_cable *cable = NULL;
+	int err = 0;
+
+	mutex_lock(&loopback->cable_lock);
+	dpcm = kzalloc(sizeof(*dpcm), GFP_KERNEL);
+	if (!dpcm) {
+		err = -ENOMEM;
+		goto unlock;
+	}
+	dpcm->loopback = loopback;
+	dpcm->substream = substream;
+	timer_setup(&dpcm->timer, loopback_timer_function, 0);
+
+	cable = loopback->cables[substream->pcm->device];
+	if (!cable) {
+		cable = kzalloc(sizeof(*cable), GFP_KERNEL);
+		if (!cable) {
+			err = -ENOMEM;
+			goto unlock;
+		}
+		spin_lock_init(&cable->lock);
+		cable->hw = loopback_pcm_hardware;
+		loopback->cables[substream->pcm->device] = cable;
+	}
+	dpcm->cable = cable;
+
+	snd_pcm_hw_constraint_integer(runtime, SNDRV_PCM_HW_PARAM_PERIODS);
+
+	/* use dynamic rules based on actual runtime->hw values */
+	/* note that the default rules created in the PCM midlevel code */
+	/* are cached -> they do not reflect the actual state */
+	err = snd_pcm_hw_rule_add(runtime, 0, SNDRV_PCM_HW_PARAM_FORMAT,
+				  rule_format, dpcm, SNDRV_PCM_HW_PARAM_FORMAT,
+				  -1);
+	if (err < 0)
+		goto unlock;
+	err = snd_pcm_hw_rule_add(runtime, 0, SNDRV_PCM_HW_PARAM_RATE,
+				  rule_rate, dpcm, SNDRV_PCM_HW_PARAM_RATE, -1);
+	if (err < 0)
+		goto unlock;
+	err = snd_pcm_hw_rule_add(runtime, 0, SNDRV_PCM_HW_PARAM_CHANNELS,
+				  rule_channels, dpcm,
+				  SNDRV_PCM_HW_PARAM_CHANNELS, -1);
+	if (err < 0)
+		goto unlock;
+
+	runtime->private_data = dpcm;
+	runtime->private_free = loopback_runtime_free;
+	if (get_notify(dpcm))
+		runtime->hw = loopback_pcm_hardware;
+	else
+		runtime->hw = cable->hw;
+
+	spin_lock_irq(&cable->lock);
+	cable->streams[substream->stream] = dpcm;
+	spin_unlock_irq(&cable->lock);
+
+unlock:
+	if (err < 0) {
+		free_cable(substream);
+		kfree(dpcm);
+	}
+	mutex_unlock(&loopback->cable_lock);
+	return err;
+}
+
+static int loopback_close(struct snd_pcm_substream *substream)
+{
+	struct loopback_pcm *dpcm = substream->runtime->private_data;
+
+	loopback_timer_stop_sync(dpcm);
+	mutex_lock(&loopback->cable_lock);
+	free_cable(substream);
+	mutex_unlock(&loopback->cable_lock);
+	return 0;
+}
+
+static const struct snd_pcm_ops loopbackap_pcm_ops = {
+	.open = loopback_open,
+	.close = loopback_close,
+	.hw_free = loopback_hw_free,
+	.prepare = loopback_prepare,
+	.trigger = loopback_trigger,
+	.pointer = loopback_pointer,
+};
+
+static int loopback_rate_shift_info(struct snd_kcontrol *kcontrol,
+				    struct snd_ctl_elem_info *uinfo)
+{
+	uinfo->type = SNDRV_CTL_ELEM_TYPE_INTEGER;
+	uinfo->count = 1;
+	uinfo->value.integer.min = 80000;
+	uinfo->value.integer.max = 120000;
+	uinfo->value.integer.step = 1;
+	return 0;
+}
+
+static int loopback_rate_shift_get(struct snd_kcontrol *kcontrol,
+				   struct snd_ctl_elem_value *ucontrol)
+{
+	struct loopback *loopback = snd_kcontrol_chip(kcontrol);
+
+	mutex_lock(&loopback->cable_lock);
+	ucontrol->value.integer.value[0] =
+		loopback->setup[kcontrol->id.device].rate_shift;
+	mutex_unlock(&loopback->cable_lock);
+	return 0;
+}
+
+static int loopback_rate_shift_put(struct snd_kcontrol *kcontrol,
+				   struct snd_ctl_elem_value *ucontrol)
+{
+	struct loopback *loopback = snd_kcontrol_chip(kcontrol);
+	unsigned int val;
+	int change = 0;
+
+	val = ucontrol->value.integer.value[0];
+	if (val < 80000)
+		val = 80000;
+	if (val > 120000)
+		val = 120000;
+	mutex_lock(&loopback->cable_lock);
+	if (val != loopback->setup[kcontrol->id.device].rate_shift) {
+		loopback->setup[kcontrol->id.device].rate_shift = val;
+		change = 1;
+	}
+	mutex_unlock(&loopback->cable_lock);
+	return change;
+}
+
+static int loopback_notify_get(struct snd_kcontrol *kcontrol,
+			       struct snd_ctl_elem_value *ucontrol)
+{
+	struct loopback *loopback = snd_kcontrol_chip(kcontrol);
+
+	mutex_lock(&loopback->cable_lock);
+	ucontrol->value.integer.value[0] =
+		loopback->setup[kcontrol->id.device].notify;
+	mutex_unlock(&loopback->cable_lock);
+	return 0;
+}
+
+static int loopback_notify_put(struct snd_kcontrol *kcontrol,
+			       struct snd_ctl_elem_value *ucontrol)
+{
+	struct loopback *loopback = snd_kcontrol_chip(kcontrol);
+	unsigned int val;
+	int change = 0;
+	val = ucontrol->value.integer.value[0] ? 1 : 0;
+	mutex_lock(&loopback->cable_lock);
+	if (val != loopback->setup[kcontrol->id.device].notify) {
+		loopback->setup[kcontrol->id.device].notify = val;
+		change = 1;
+	}
+	mutex_unlock(&loopback->cable_lock);
+	return change;
+}
+
+static int loopback_active_get(struct snd_kcontrol *kcontrol,
+			       struct snd_ctl_elem_value *ucontrol)
+{
+	struct loopback *loopback = snd_kcontrol_chip(kcontrol);
+	struct loopback_cable *cable;
+
+	unsigned int val = 0;
+
+	mutex_lock(&loopback->cable_lock);
+	cable = loopback->cables[kcontrol->id.device];
+	if (cable != NULL) {
+		unsigned int running = cable->running ^ cable->pause;
+
+		val = (running & (1 << SNDRV_PCM_STREAM_PLAYBACK)) ? 1 : 0;
+	}
+	mutex_unlock(&loopback->cable_lock);
+	ucontrol->value.integer.value[0] = val;
+	return 0;
+}
+
+static int loopback_format_info(struct snd_kcontrol *kcontrol,
+				struct snd_ctl_elem_info *uinfo)
+{
+	uinfo->type = SNDRV_CTL_ELEM_TYPE_INTEGER;
+	uinfo->count = 1;
+	uinfo->value.integer.min = 0;
+	uinfo->value.integer.max = SNDRV_PCM_FORMAT_LAST;
+	uinfo->value.integer.step = 1;
+	return 0;
+}
+
+static int loopback_format_get(struct snd_kcontrol *kcontrol,
+			       struct snd_ctl_elem_value *ucontrol)
+{
+	struct loopback *loopback = snd_kcontrol_chip(kcontrol);
+
+	ucontrol->value.integer.value[0] =
+		loopback->setup[kcontrol->id.device].format;
+	return 0;
+}
+
+static int loopback_rate_info(struct snd_kcontrol *kcontrol,
+			      struct snd_ctl_elem_info *uinfo)
+{
+	uinfo->type = SNDRV_CTL_ELEM_TYPE_INTEGER;
+	uinfo->count = 1;
+	uinfo->value.integer.min = 0;
+	uinfo->value.integer.max = 192000;
+	uinfo->value.integer.step = 1;
+	return 0;
+}
 
-	AP_INFOK("%s\n%s\n%d\n%d", substream->pcm->name,
-		 substream->stream == SNDRV_PCM_STREAM_PLAYBACK ? "PLAYBACK" :
-								  "CAPTURE",
-		 runtime->rate, runtime->channels);
+static int loopback_rate_get(struct snd_kcontrol *kcontrol,
+			     struct snd_ctl_elem_value *ucontrol)
+{
+	struct loopback *loopback = snd_kcontrol_chip(kcontrol);
+	mutex_lock(&loopback->cable_lock);
+	ucontrol->value.integer.value[0] =
+		loopback->setup[kcontrol->id.device].rate;
+	mutex_unlock(&loopback->cable_lock);
+	return 0;
+}
 
-	return systimer_prepare(substream);
+static int loopback_channels_info(struct snd_kcontrol *kcontrol,
+				  struct snd_ctl_elem_info *uinfo)
+{
+	uinfo->type = SNDRV_CTL_ELEM_TYPE_INTEGER;
+	uinfo->count = 1;
+	uinfo->value.integer.min = 1;
+	uinfo->value.integer.max = 1024;
+	uinfo->value.integer.step = 1;
+	return 0;
 }
 
-static struct snd_pcm_ops loopbackap_pcm_ops = {
-	.open = loopback_pcm_open,
-	.close = loopback_pcm_close,
-	.prepare = loopback_pcm_prepare,
-	.pointer = loopback_pcm_pointer,
-	.trigger = loopback_pcm_trigger,
+static int loopback_channels_get(struct snd_kcontrol *kcontrol,
+				 struct snd_ctl_elem_value *ucontrol)
+{
+	struct loopback *loopback = snd_kcontrol_chip(kcontrol);
+
+	mutex_lock(&loopback->cable_lock);
+	ucontrol->value.integer.value[0] =
+		loopback->setup[kcontrol->id.device].channels;
+	mutex_unlock(&loopback->cable_lock);
+	return 0;
+}
+
+static struct snd_kcontrol_new loopback_controls[] = {
+	{
+		.iface = SNDRV_CTL_ELEM_IFACE_PCM,
+		.name = "PCM Rate Shift 100000",
+		.info = loopback_rate_shift_info,
+		.get = loopback_rate_shift_get,
+		.put = loopback_rate_shift_put,
+	},
+	{
+		.iface = SNDRV_CTL_ELEM_IFACE_PCM,
+		.name = "PCM Notify",
+		.info = snd_ctl_boolean_mono_info,
+		.get = loopback_notify_get,
+		.put = loopback_notify_put,
+	},
+#define ACTIVE_IDX 2
+	{
+		.access = SNDRV_CTL_ELEM_ACCESS_READ,
+		.iface = SNDRV_CTL_ELEM_IFACE_PCM,
+		.name = "PCM Slave Active",
+		.info = snd_ctl_boolean_mono_info,
+		.get = loopback_active_get,
+	},
+#define FORMAT_IDX 3
+	{ .access = SNDRV_CTL_ELEM_ACCESS_READ,
+	  .iface = SNDRV_CTL_ELEM_IFACE_PCM,
+	  .name = "PCM Slave Format",
+	  .info = loopback_format_info,
+	  .get = loopback_format_get },
+#define RATE_IDX 4
+	{ .access = SNDRV_CTL_ELEM_ACCESS_READ,
+	  .iface = SNDRV_CTL_ELEM_IFACE_PCM,
+	  .name = "PCM Slave Rate",
+	  .info = loopback_rate_info,
+	  .get = loopback_rate_get },
+#define CHANNELS_IDX 5
+	{ .access = SNDRV_CTL_ELEM_ACCESS_READ,
+	  .iface = SNDRV_CTL_ELEM_IFACE_PCM,
+	  .name = "PCM Slave Channels",
+	  .info = loopback_channels_info,
+	  .get = loopback_channels_get }
 };
 
+static int loopback_mixer_new(struct loopback *loopback, int notify)
+{
+	struct snd_card *card = loopback->card;
+	struct snd_pcm *pcm;
+	struct snd_kcontrol *kctl;
+	struct loopback_setup *setup;
+	int dev, dev_count, idx, err;
+
+	strcpy(card->mixername, "Loopback Mixer");
+	dev_count = avirt_stream_count(SNDRV_PCM_STREAM_PLAYBACK);
+	for (dev = 0; dev < dev_count; dev++) {
+		pcm = loopback->pcm[dev];
+		setup = &loopback->setup[dev];
+		setup->notify = notify;
+		setup->rate_shift = NO_PITCH;
+		setup->format = SNDRV_PCM_FORMAT_S16_LE;
+		setup->rate = 48000;
+		setup->channels = 2;
+		for (idx = 0; idx < ARRAY_SIZE(loopback_controls); idx++) {
+			kctl = snd_ctl_new1(&loopback_controls[idx], loopback);
+			if (!kctl)
+				return -ENOMEM;
+			kctl->id.device = dev;
+			kctl->id.subdevice = 0;
+			switch (idx) {
+			case ACTIVE_IDX:
+				setup->active_id = kctl->id;
+				break;
+			case FORMAT_IDX:
+				setup->format_id = kctl->id;
+				break;
+			case RATE_IDX:
+				setup->rate_id = kctl->id;
+				break;
+			case CHANNELS_IDX:
+				setup->channels_id = kctl->id;
+				break;
+			default:
+				break;
+			}
+			err = snd_ctl_add(card, kctl);
+			if (err < 0)
+				return err;
+		}
+	}
+	return 0;
+}
+
+static void print_dpcm_info(struct snd_info_buffer *buffer,
+			    struct loopback_pcm *dpcm, const char *id)
+{
+	snd_iprintf(buffer, "  %s\n", id);
+	if (dpcm == NULL) {
+		snd_iprintf(buffer, "    inactive\n");
+		return;
+	}
+	snd_iprintf(buffer, "    buffer_size:\t%u\n", dpcm->pcm_buffer_size);
+	snd_iprintf(buffer, "    buffer_pos:\t\t%u\n", dpcm->buf_pos);
+	snd_iprintf(buffer, "    silent_size:\t%u\n", dpcm->silent_size);
+	snd_iprintf(buffer, "    period_size:\t%u\n", dpcm->pcm_period_size);
+	snd_iprintf(buffer, "    bytes_per_sec:\t%u\n", dpcm->pcm_bps);
+	snd_iprintf(buffer, "    sample_align:\t%u\n", dpcm->pcm_salign);
+	snd_iprintf(buffer, "    rate_shift:\t\t%u\n", dpcm->pcm_rate_shift);
+	snd_iprintf(buffer, "    update_pending:\t%u\n",
+		    dpcm->period_update_pending);
+	snd_iprintf(buffer, "    irq_pos:\t\t%u\n", dpcm->irq_pos);
+	snd_iprintf(buffer, "    period_frac:\t%u\n", dpcm->period_size_frac);
+	snd_iprintf(buffer, "    last_jiffies:\t%lu (%lu)\n",
+		    dpcm->last_jiffies, jiffies);
+	snd_iprintf(buffer, "    timer_expires:\t%lu\n", dpcm->timer.expires);
+}
+
+static void print_substream_info(struct snd_info_buffer *buffer,
+				 struct loopback *loopback, int device)
+{
+	struct loopback_cable *cable = loopback->cables[device];
+
+	snd_iprintf(buffer, "Cable device %i:\n", device);
+	if (cable == NULL) {
+		snd_iprintf(buffer, "  inactive\n");
+		return;
+	}
+	snd_iprintf(buffer, "  valid: %u\n", cable->valid);
+	snd_iprintf(buffer, "  running: %u\n", cable->running);
+	snd_iprintf(buffer, "  pause: %u\n", cable->pause);
+	print_dpcm_info(buffer, cable->streams[0], "Playback");
+	print_dpcm_info(buffer, cable->streams[1], "Capture");
+}
+
+static void print_cable_info(struct snd_info_entry *entry,
+			     struct snd_info_buffer *buffer)
+{
+	struct loopback *loopback = entry->private_data;
+	int device;
+
+	mutex_lock(&loopback->cable_lock);
+	for (device = 0; device < MAX_STREAMS; device++)
+		print_substream_info(buffer, loopback, device);
+	mutex_unlock(&loopback->cable_lock);
+}
+
+static int loopback_proc_new(struct loopback *loopback, int cidx)
+{
+	char name[32];
+	struct snd_info_entry *entry;
+	int err;
+
+	snprintf(name, sizeof(name), "cable#%d", cidx);
+	err = snd_card_proc_new(loopback->card, name, &entry);
+	if (err < 0)
+		return err;
+
+	snd_info_set_text_ops(entry, loopback, print_cable_info);
+	return 0;
+}
+
+int loopbackap_configure(struct snd_card *card,
+			 struct config_group *avirt_stream_group,
+			 unsigned int stream_count)
+{
+	int err;
+	struct list_head *entry;
+
+	loopback = kzalloc(sizeof(struct loopback), GFP_KERNEL);
+	if (!loopback)
+		return -ENOMEM;
+	loopback->card = card;
+	mutex_init(&loopback->cable_lock);
+
+	list_for_each (entry, &avirt_stream_group->cg_children) {
+		struct config_item *item =
+			container_of(entry, struct config_item, ci_entry);
+		struct avirt_stream *stream =
+			avirt_stream_from_config_item(item);
+		loopback->pcm[stream->device] = stream->pcm;
+
+		AP_INFOK("stream name:%s device:%d channels:%d", stream->name,
+			 stream->device, stream->channels);
+	}
+
+	err = loopback_mixer_new(loopback, 1);
+	if (err < 0)
+		return err;
+
+	loopback_proc_new(loopback, 0);
+	loopback_proc_new(loopback, 1);
+
+	return 0;
+}
+
 /*******************************************************************************
  * Loopback Audio Path AVIRT registration
  ******************************************************************************/
-static struct snd_pcm_hardware loopbackap_hw = {
-	.formats = SNDRV_PCM_FMTBIT_S16_LE,
-	.info = (SNDRV_PCM_INFO_INTERLEAVED // Channel interleaved audio
-		 | SNDRV_PCM_INFO_BLOCK_TRANSFER | SNDRV_PCM_INFO_MMAP |
-		 SNDRV_PCM_INFO_MMAP_VALID),
-	/*
-	.rates = SNDRV_PCM_RATE_8000 | SNDRV_PCM_RATE_16000 |
-		 SNDRV_PCM_RATE_32000 | SNDRV_PCM_RATE_44100 |
-		 SNDRV_PCM_RATE_48000,
-	.rate_min = 8000,
-	.rate_max = 48000,
-	*/
-	.rates = SNDRV_PCM_RATE_48000,
-	.rate_min = 48000,
-	.rate_max = 48000,
-	.channels_min = 1,
-	.channels_max = 8,
-	//.buffer_bytes_max = 32768,
-	.periods_min = 1,
-	.periods_max = 8,
-};
-
 static struct avirt_audiopath loopbackap_module = {
+	.uid = AP_UID,
 	.name = "Loopback Audio Path",
 	.version = { 0, 0, 1 },
-	.value = 10,
-	.hw = &loopbackap_hw,
+	.hw = &loopback_pcm_hardware,
 	.pcm_ops = &loopbackap_pcm_ops,
-	.configure = loopback_configure,
+	.configure = loopbackap_configure,
 };
 
-static int __init loopback_init(void)
+static int __init alsa_card_loopback_init(void)
 {
 	int err = 0;
 
-	AP_INFOK("init()");
-
-	err = avirt_register_audiopath(&loopbackap_module, &coreinfo);
+	err = avirt_audiopath_register(&loopbackap_module, &coreinfo);
 	if ((err < 0) || (!coreinfo)) {
-		AP_ERRORK("%s: coreinfo is NULL!\n", __func__);
+		AP_ERRORK("coreinfo is NULL!");
 		return err;
 	}
 
-	return err;
+	return 0;
 }
 
-static void __exit loopback_exit(void)
+static void __exit alsa_card_loopback_exit(void)
 {
-	AP_INFOK("loopback: exit()");
-
-	avirt_deregister_audiopath(&loopbackap_module);
+	avirt_audiopath_deregister(&loopbackap_module);
 }
 
-module_init(loopback_init);
-module_exit(loopback_exit);
+module_init(alsa_card_loopback_init);
+module_exit(alsa_card_loopback_exit)
diff --git a/scripts/load.sh b/scripts/load.sh
index 2cd472d..82f613a 100755
--- a/scripts/load.sh
+++ b/scripts/load.sh
@@ -4,7 +4,10 @@
 insmod avirt_core.ko
 
 # Load the additional Audio Paths
-#insmod dummy/avirt_dummyap.ko
+insmod dummy/avirt_dummyap.ko
 insmod loopback/avirt_loopbackap.ko
 
+# Run the test script
+./scripts/test_configfs.sh
+
 echo "Drivers Loaded!"
diff --git a/scripts/test_configfs.sh b/scripts/test_configfs.sh
index 1ae0fe5..baa5e58 100755
--- a/scripts/test_configfs.sh
+++ b/scripts/test_configfs.sh
@@ -4,14 +4,18 @@ mkdir -p /config && mount -t configfs none /config
 
 mkdir /config/avirt/streams/playback_media
 echo "2">/config/avirt/streams/playback_media/channels
+echo "ap_loopback">/config/avirt/streams/playback_media/map
 
 mkdir /config/avirt/streams/playback_navigation
 echo "1">/config/avirt/streams/playback_navigation/channels
+echo "ap_loopback">/config/avirt/streams/playback_navigation/map
 
 mkdir /config/avirt/streams/playback_emergency
 echo "1">/config/avirt/streams/playback_emergency/channels
+echo "ap_loopback">/config/avirt/streams/playback_emergency/map
 
 mkdir /config/avirt/streams/capture_voice
 echo "1">/config/avirt/streams/capture_voice/channels
+echo "ap_loopback">/config/avirt/streams/capture_voice/map
 
 echo "1">/config/avirt/streams/sealed
diff --git a/scripts/unload.sh b/scripts/unload.sh
index a011a2b..2c158d5 100755
--- a/scripts/unload.sh
+++ b/scripts/unload.sh
@@ -1,5 +1,8 @@
 #!/bin/sh
 
+rmdir /config/avirt/streams/playback_*
+rmdir /config/avirt/streams/capture_*
+
 rm_module() {
         lsmod |grep "^$1\>" && rmmod $1 || true
 }