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aloop.c

/*
 *  Loopback soundcard
 *
 *  Original code:
 *  Copyright (c) by Jaroslav Kysela <perex@perex.cz>
 *
 *  More accurate positioning and full-duplex support:
 *  Copyright (c) Ahmet ─░nan <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>
 *
 *   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
 *
 */

#include <linux/init.h>
#include <linux/jiffies.h>
#include <linux/slab.h>
#include <linux/time.h>
#include <linux/wait.h>
#include <linux/moduleparam.h>
#include <linux/platform_device.h>
#include <sound/core.h>
#include <sound/control.h>
#include <sound/pcm.h>
#include <sound/info.h>
#include <sound/initval.h>

MODULE_AUTHOR("Jaroslav Kysela <perex@perex.cz>");
MODULE_DESCRIPTION("A loopback soundcard");
MODULE_LICENSE("GPL");
MODULE_SUPPORTED_DEVICE("{{ALSA,Loopback soundcard}}");

#define MAX_PCM_SUBSTREAMS    8

static int index[SNDRV_CARDS] = SNDRV_DEFAULT_IDX;    /* Index 0-MAX */
static char *id[SNDRV_CARDS] = SNDRV_DEFAULT_STR;     /* ID for this card */
static int enable[SNDRV_CARDS] = {1, [1 ... (SNDRV_CARDS - 1)] = 0};
static int pcm_substreams[SNDRV_CARDS] = {[0 ... (SNDRV_CARDS - 1)] = 8};
static int pcm_notify[SNDRV_CARDS];

module_param_array(index, int, NULL, 0444);
MODULE_PARM_DESC(index, "Index value for loopback soundcard.");
module_param_array(id, charp, NULL, 0444);
MODULE_PARM_DESC(id, "ID string for loopback soundcard.");
module_param_array(enable, bool, NULL, 0444);
MODULE_PARM_DESC(enable, "Enable this loopback soundcard.");
module_param_array(pcm_substreams, int, NULL, 0444);
MODULE_PARM_DESC(pcm_substreams, "PCM substreams # (1-8) for loopback driver.");
module_param_array(pcm_notify, int, NULL, 0444);
MODULE_PARM_DESC(pcm_notify, "Break capture when PCM format/rate/channels changes.");

#define NO_PITCH 100000

struct loopback_pcm;

00073 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;
};

00083 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;
};

00095 struct loopback {
      struct snd_card *card;
      struct mutex cable_lock;
      struct loopback_cable *cables[MAX_PCM_SUBSTREAMS][2];
      struct snd_pcm *pcm[2];
      struct loopback_setup setup[MAX_PCM_SUBSTREAMS][2];
};

00103 struct loopback_pcm {
      struct loopback *loopback;
      struct snd_pcm_substream *substream;
      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 long last_jiffies;
      struct timer_list timer;
};

static struct platform_device *devices[SNDRV_CARDS];

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);
}

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;
}

static inline struct loopback_setup *get_setup(struct loopback_pcm *dpcm)
{
      int device = dpcm->substream->pstr->pcm->device;
      
      if (dpcm->substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
            device ^= 1;
      return &dpcm->loopback->setup[dpcm->substream->number][device];
}

static inline unsigned int get_notify(struct loopback_pcm *dpcm)
{
      return get_setup(dpcm)->notify;
}

static inline unsigned int get_rate_shift(struct loopback_pcm *dpcm)
{
      return get_setup(dpcm)->rate_shift;
}

static void loopback_timer_start(struct loopback_pcm *dpcm)
{
      unsigned long tick;
      unsigned int rate_shift = get_rate_shift(dpcm);

      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;
      dpcm->timer.expires = jiffies + tick;
      add_timer(&dpcm->timer);
}

static inline void loopback_timer_stop(struct loopback_pcm *dpcm)
{
      del_timer(&dpcm->timer);
      dpcm->timer.expires = 0;
}

#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;
}

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;
      struct loopback_cable *cable = dpcm->cable;
      int err, stream = 1 << substream->stream;

      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;
            spin_lock(&cable->lock);      
            cable->running |= stream;
            cable->pause &= ~stream;
            spin_unlock(&cable->lock);
            loopback_timer_start(dpcm);
            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;
            spin_unlock(&cable->lock);
            loopback_timer_stop(dpcm);
            if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
                  loopback_active_notify(dpcm);
            break;
      case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
            spin_lock(&cable->lock);      
            cable->pause |= stream;
            spin_unlock(&cable->lock);
            loopback_timer_stop(dpcm);
            break;
      case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
            spin_lock(&cable->lock);
            dpcm->last_jiffies = jiffies;
            cable->pause &= ~stream;
            spin_unlock(&cable->lock);
            loopback_timer_start(dpcm);
            break;
      default:
            return -EINVAL;
      }
      return 0;
}

static void params_change_substream(struct loopback_pcm *dpcm,
                            struct snd_pcm_runtime *runtime)
{
      struct snd_pcm_runtime *dst_runtime;

      if (dpcm == NULL || dpcm->substream == NULL)
            return;
      dst_runtime = dpcm->substream->runtime;
      if (dst_runtime == NULL)
            return;
      dst_runtime->hw = dpcm->cable->hw;
}

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;

      cable->hw.formats = (1ULL << 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;
      params_change_substream(cable->streams[SNDRV_PCM_STREAM_PLAYBACK],
                        runtime);
      params_change_substream(cable->streams[SNDRV_PCM_STREAM_CAPTURE],
                        runtime);
}

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;

      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;
}

static void clear_capture_buf(struct loopback_pcm *dpcm, unsigned int bytes)
{
      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;
      }
}

static void copy_play_buf(struct loopback_pcm *play,
                    struct loopback_pcm *capt,
                    unsigned int bytes)
{
      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;

      /* 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;
      }
}

#define BYTEPOS_UPDATE_POSONLY      0
#define BYTEPOS_UPDATE_CLEAR  1
#define BYTEPOS_UPDATE_COPY   2

static void loopback_bytepos_update(struct loopback_pcm *dpcm,
                            unsigned int delta,
                            unsigned int cmd)
{
      unsigned int count;
      unsigned long last_pos;

      last_pos = byte_pos(dpcm, dpcm->irq_pos);
      dpcm->irq_pos += delta * dpcm->pcm_bps;
      count = byte_pos(dpcm, dpcm->irq_pos) - last_pos;
      if (!count)
            return;
      if (cmd == BYTEPOS_UPDATE_CLEAR)
            clear_capture_buf(dpcm, count);
      else if (cmd == BYTEPOS_UPDATE_COPY)
            copy_play_buf(dpcm->cable->streams[SNDRV_PCM_STREAM_PLAYBACK],
                        dpcm->cable->streams[SNDRV_PCM_STREAM_CAPTURE],
                        count);
      dpcm->buf_pos += count;
      dpcm->buf_pos %= dpcm->pcm_buffer_size;
      if (dpcm->irq_pos >= dpcm->period_size_frac) {
            dpcm->irq_pos %= dpcm->period_size_frac;
            dpcm->period_update_pending = 1;
      }
}

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;

      spin_lock(&cable->lock);      
      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;
      }

      if (delta_play == 0 && delta_capt == 0) {
            spin_unlock(&cable->lock);
            return running;
      }
            
      if (delta_play > delta_capt) {
            loopback_bytepos_update(dpcm_play, delta_play - delta_capt,
                              BYTEPOS_UPDATE_POSONLY);
            delta_play = delta_capt;
      } else if (delta_play < delta_capt) {
            loopback_bytepos_update(dpcm_capt, delta_capt - delta_play,
                              BYTEPOS_UPDATE_CLEAR);
            delta_capt = delta_play;
      }

      if (delta_play == 0 && delta_capt == 0) {
            spin_unlock(&cable->lock);
            return running;
      }
      /* note delta_capt == delta_play at this moment */
      loopback_bytepos_update(dpcm_capt, delta_capt, BYTEPOS_UPDATE_COPY);
      loopback_bytepos_update(dpcm_play, delta_play, BYTEPOS_UPDATE_POSONLY);
      spin_unlock(&cable->lock);
      return running;
}

static void loopback_timer_function(unsigned long data)
{
      struct loopback_pcm *dpcm = (struct loopback_pcm *)data;
      unsigned int running;

      running = loopback_pos_update(dpcm->cable);
      if (running & (1 << dpcm->substream->stream)) {
            loopback_timer_start(dpcm);
            if (dpcm->period_update_pending) {
                  dpcm->period_update_pending = 0;
                  snd_pcm_period_elapsed(dpcm->substream);
            }
      }
}

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;

      loopback_pos_update(dpcm->cable);
      return bytes_to_frames(runtime, dpcm->buf_pos);
}

static 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),
      .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_hw_params(struct snd_pcm_substream *substream,
                        struct snd_pcm_hw_params *params)
{
      return snd_pcm_lib_malloc_pages(substream, params_buffer_bytes(params));
}

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;

      mutex_lock(&dpcm->loopback->cable_lock);
      cable->valid &= ~(1 << substream->stream);
      mutex_unlock(&dpcm->loopback->cable_lock);
      return snd_pcm_lib_free_pages(substream);
}

static unsigned int get_cable_index(struct snd_pcm_substream *substream)
{
      if (!substream->pcm->device)
            return substream->stream;
      else
            return !substream->stream;
}

static int rule_format(struct snd_pcm_hw_params *params,
                   struct snd_pcm_hw_rule *rule)
{

      struct snd_pcm_hardware *hw = rule->private;
      struct snd_mask *maskp = hw_param_mask(params, rule->var);

      maskp->bits[0] &= (u_int32_t)hw->formats;
      maskp->bits[1] &= (u_int32_t)(hw->formats >> 32);
      memset(maskp->bits + 2, 0, (SNDRV_MASK_MAX-64) / 8); /* clear rest */
      if (! maskp->bits[0] && ! maskp->bits[1])
            return -EINVAL;
      return 0;
}

static int rule_rate(struct snd_pcm_hw_params *params,
                 struct snd_pcm_hw_rule *rule)
{
      struct snd_pcm_hardware *hw = rule->private;
      struct snd_interval t;

        t.min = hw->rate_min;
        t.max = hw->rate_max;
        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 snd_pcm_hardware *hw = rule->private;
      struct snd_interval t;

        t.min = hw->channels_min;
        t.max = hw->channels_max;
        t.openmin = t.openmax = 0;
        t.integer = 0;
      return snd_interval_refine(hw_param_interval(params, rule->var), &t);
}

static int loopback_open(struct snd_pcm_substream *substream)
{
      struct snd_pcm_runtime *runtime = substream->runtime;
      struct loopback *loopback = substream->private_data;
      struct loopback_pcm *dpcm;
      struct loopback_cable *cable;
      int err = 0;
      int dev = get_cable_index(substream);

      mutex_lock(&loopback->cable_lock);
      dpcm = kzalloc(sizeof(*dpcm), GFP_KERNEL);
      if (!dpcm) {
            err = -ENOMEM;
            goto unlock;
      }
      dpcm->loopback = loopback;
      dpcm->substream = substream;
      setup_timer(&dpcm->timer, loopback_timer_function,
                (unsigned long)dpcm);

      cable = loopback->cables[substream->number][dev];
      if (!cable) {
            cable = kzalloc(sizeof(*cable), GFP_KERNEL);
            if (!cable) {
                  kfree(dpcm);
                  err = -ENOMEM;
                  goto unlock;
            }
            spin_lock_init(&cable->lock);
            cable->hw = loopback_pcm_hardware;
            loopback->cables[substream->number][dev] = cable;
      }
      dpcm->cable = cable;
      cable->streams[substream->stream] = dpcm;

      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, &runtime->hw,
                          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, &runtime->hw,
                          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, &runtime->hw,
                          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;
 unlock:
      mutex_unlock(&loopback->cable_lock);
      return err;
}

static int loopback_close(struct snd_pcm_substream *substream)
{
      struct loopback *loopback = substream->private_data;
      struct loopback_pcm *dpcm = substream->runtime->private_data;
      struct loopback_cable *cable;
      int dev = get_cable_index(substream);

      loopback_timer_stop(dpcm);
      mutex_lock(&loopback->cable_lock);
      cable = loopback->cables[substream->number][dev];
      if (cable->streams[!substream->stream]) {
            /* other stream is still alive */
            cable->streams[substream->stream] = NULL;
      } else {
            /* free the cable */
            loopback->cables[substream->number][dev] = NULL;
            kfree(cable);
      }
      mutex_unlock(&loopback->cable_lock);
      return 0;
}

static struct snd_pcm_ops loopback_playback_ops = {
      .open =           loopback_open,
      .close =    loopback_close,
      .ioctl =    snd_pcm_lib_ioctl,
      .hw_params =      loopback_hw_params,
      .hw_free =  loopback_hw_free,
      .prepare =  loopback_prepare,
      .trigger =  loopback_trigger,
      .pointer =  loopback_pointer,
};

static struct snd_pcm_ops loopback_capture_ops = {
      .open =           loopback_open,
      .close =    loopback_close,
      .ioctl =    snd_pcm_lib_ioctl,
      .hw_params =      loopback_hw_params,
      .hw_free =  loopback_hw_free,
      .prepare =  loopback_prepare,
      .trigger =  loopback_trigger,
      .pointer =  loopback_pointer,
};

static int __devinit loopback_pcm_new(struct loopback *loopback,
                              int device, int substreams)
{
      struct snd_pcm *pcm;
      int err;

      err = snd_pcm_new(loopback->card, "Loopback PCM", device,
                    substreams, substreams, &pcm);
      if (err < 0)
            return err;
      snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK, &loopback_playback_ops);
      snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_CAPTURE, &loopback_capture_ops);

      pcm->private_data = loopback;
      pcm->info_flags = 0;
      strcpy(pcm->name, "Loopback PCM");

      loopback->pcm[device] = pcm;

      snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_CONTINUOUS,
                  snd_dma_continuous_data(GFP_KERNEL),
                  0, 2 * 1024 * 1024);
      return 0;
}

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);
      
      ucontrol->value.integer.value[0] =
            loopback->setup[kcontrol->id.subdevice]
                         [kcontrol->id.device].rate_shift;
      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.subdevice]
                          [kcontrol->id.device].rate_shift) {
            loopback->setup[kcontrol->id.subdevice]
                         [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);
      
      ucontrol->value.integer.value[0] =
            loopback->setup[kcontrol->id.subdevice]
                         [kcontrol->id.device].notify;
      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;
      if (val != loopback->setup[kcontrol->id.subdevice]
                        [kcontrol->id.device].notify) {
            loopback->setup[kcontrol->id.subdevice]
                  [kcontrol->id.device].notify = val;
            change = 1;
      }
      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 = loopback->cables
                  [kcontrol->id.subdevice][kcontrol->id.device ^ 1];
      unsigned int val = 0;

      if (cable != NULL)
            val = (cable->running & (1 << SNDRV_PCM_STREAM_PLAYBACK)) ?
                                                      1 : 0;
      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.subdevice]
                         [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;
}                                  

static int loopback_rate_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.subdevice]
                         [kcontrol->id.device].rate;
      return 0;
}

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 int loopback_channels_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.subdevice]
                         [kcontrol->id.device].channels;
      return 0;
}

static struct snd_kcontrol_new loopback_controls[]  __devinitdata = {
{
      .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 __devinit 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 err, dev, substr, substr_count, idx;

      strcpy(card->mixername, "Loopback Mixer");
      for (dev = 0; dev < 2; dev++) {
            pcm = loopback->pcm[dev];
            substr_count =
                pcm->streams[SNDRV_PCM_STREAM_CAPTURE].substream_count;
            for (substr = 0; substr < substr_count; substr++) {
                  setup = &loopback->setup[substr][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 = substr;
                        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;
}

#ifdef CONFIG_PROC_FS

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 sub,
                         int num)
{
      struct loopback_cable *cable = loopback->cables[sub][num];

      snd_iprintf(buffer, "Cable %i substream %i:\n", num, sub);
      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 sub, num;

      mutex_lock(&loopback->cable_lock);
      num = entry->name[strlen(entry->name)-1];
      num = num == '0' ? 0 : 1;
      for (sub = 0; sub < MAX_PCM_SUBSTREAMS; sub++)
            print_substream_info(buffer, loopback, sub, num);
      mutex_unlock(&loopback->cable_lock);
}

static int __devinit 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;
}

#else /* !CONFIG_PROC_FS */

#define loopback_proc_new(loopback, cidx) do { } while (0)

#endif

static int __devinit loopback_probe(struct platform_device *devptr)
{
      struct snd_card *card;
      struct loopback *loopback;
      int dev = devptr->id;
      int err;

      err = snd_card_create(index[dev], id[dev], THIS_MODULE,
                        sizeof(struct loopback), &card);
      if (err < 0)
            return err;
      loopback = card->private_data;

      if (pcm_substreams[dev] < 1)
            pcm_substreams[dev] = 1;
      if (pcm_substreams[dev] > MAX_PCM_SUBSTREAMS)
            pcm_substreams[dev] = MAX_PCM_SUBSTREAMS;
      
      loopback->card = card;
      mutex_init(&loopback->cable_lock);

      err = loopback_pcm_new(loopback, 0, pcm_substreams[dev]);
      if (err < 0)
            goto __nodev;
      err = loopback_pcm_new(loopback, 1, pcm_substreams[dev]);
      if (err < 0)
            goto __nodev;
      err = loopback_mixer_new(loopback, pcm_notify[dev] ? 1 : 0);
      if (err < 0)
            goto __nodev;
      loopback_proc_new(loopback, 0);
      loopback_proc_new(loopback, 1);
      strcpy(card->driver, "Loopback");
      strcpy(card->shortname, "Loopback");
      sprintf(card->longname, "Loopback %i", dev + 1);
      err = snd_card_register(card);
      if (!err) {
            platform_set_drvdata(devptr, card);
            return 0;
      }
      __nodev:
      snd_card_free(card);
      return err;
}

static int __devexit loopback_remove(struct platform_device *devptr)
{
      snd_card_free(platform_get_drvdata(devptr));
      platform_set_drvdata(devptr, NULL);
      return 0;
}

#ifdef CONFIG_PM
static int loopback_suspend(struct platform_device *pdev,
                        pm_message_t state)
{
      struct snd_card *card = platform_get_drvdata(pdev);
      struct loopback *loopback = card->private_data;

      snd_power_change_state(card, SNDRV_CTL_POWER_D3hot);

      snd_pcm_suspend_all(loopback->pcm[0]);
      snd_pcm_suspend_all(loopback->pcm[1]);
      return 0;
}
      
static int loopback_resume(struct platform_device *pdev)
{
      struct snd_card *card = platform_get_drvdata(pdev);

      snd_power_change_state(card, SNDRV_CTL_POWER_D0);
      return 0;
}
#endif

#define SND_LOOPBACK_DRIVER   "snd_aloop"

static struct platform_driver loopback_driver = {
      .probe            = loopback_probe,
      .remove           = __devexit_p(loopback_remove),
#ifdef CONFIG_PM
      .suspend    = loopback_suspend,
      .resume           = loopback_resume,
#endif
      .driver           = {
            .name = SND_LOOPBACK_DRIVER
      },
};

static void loopback_unregister_all(void)
{
      int i;

      for (i = 0; i < ARRAY_SIZE(devices); ++i)
            platform_device_unregister(devices[i]);
      platform_driver_unregister(&loopback_driver);
}

static int __init alsa_card_loopback_init(void)
{
      int i, err, cards;

      err = platform_driver_register(&loopback_driver);
      if (err < 0)
            return err;


      cards = 0;
      for (i = 0; i < SNDRV_CARDS; i++) {
            struct platform_device *device;
            if (!enable[i])
                  continue;
            device = platform_device_register_simple(SND_LOOPBACK_DRIVER,
                                           i, NULL, 0);
            if (IS_ERR(device))
                  continue;
            if (!platform_get_drvdata(device)) {
                  platform_device_unregister(device);
                  continue;
            }
            devices[i] = device;
            cards++;
      }
      if (!cards) {
#ifdef MODULE
            printk(KERN_ERR "aloop: No loopback enabled\n");
#endif
            loopback_unregister_all();
            return -ENODEV;
      }
      return 0;
}

static void __exit alsa_card_loopback_exit(void)
{
      loopback_unregister_all();
}

module_init(alsa_card_loopback_init)
module_exit(alsa_card_loopback_exit)

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