// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *  Loopback soundcard
 *
 *  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>
 */

#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 <sound/timer.h>

MODULE_AUTHOR("Jaroslav Kysela <perex@perex.cz>");
MODULE_DESCRIPTION("A loopback soundcard");
MODULE_LICENSE("GPL");

#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 bool 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];
static char *timer_source[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.");
module_param_array(timer_source, charp, NULL, 0444);
MODULE_PARM_DESC(timer_source, "Sound card name or number and device/subdevice number of timer to be used. Empty string for jiffies timer [default].");

#define NO_PITCH 100000

#define CABLE_VALID_PLAYBACK    BIT(SNDRV_PCM_STREAM_PLAYBACK)
#define CABLE_VALID_CAPTURE     BIT(SNDRV_PCM_STREAM_CAPTURE)
#define CABLE_VALID_BOTH        (CABLE_VALID_PLAYBACK | CABLE_VALID_CAPTURE)

struct loopback_cable;
struct loopback_pcm;

struct loopback_ops {
        /* optional
         * call in loopback->cable_lock
         */
        int (*open)(struct loopback_pcm *dpcm);
        /* required
         * call in cable->lock
         */
        int (*start)(struct loopback_pcm *dpcm);
        /* required
         * call in cable->lock
         */
        int (*stop)(struct loopback_pcm *dpcm);
        /* optional */
        int (*stop_sync)(struct loopback_pcm *dpcm);
        /* optional */
        int (*close_substream)(struct loopback_pcm *dpcm);
        /* optional
         * call in loopback->cable_lock
         */
        int (*close_cable)(struct loopback_pcm *dpcm);
        /* optional
         * call in cable->lock
         */
        unsigned int (*pos_update)(struct loopback_cable *cable);
        /* optional */
        void (*dpcm_info)(struct loopback_pcm *dpcm,
                          struct snd_info_buffer *buffer);
};

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;
        /* timer specific */
        const struct loopback_ops *ops;
        /* If sound timer is used */
        struct {
                int stream;
                struct snd_timer_id id;
                struct work_struct event_work;
                struct snd_timer_instance *instance;
        } snd_timer;
};

struct loopback_setup {
        unsigned int notify: 1;
        unsigned int rate_shift;
        snd_pcm_format_t 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_PCM_SUBSTREAMS][2];
        struct snd_pcm *pcm[2];
        struct loopback_setup setup[MAX_PCM_SUBSTREAMS][2];
        const char *timer_source;
};

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 in jiffies
                                         * ticks
                                         */
        unsigned int period_size_frac;  /* period size in jiffies ticks */
        unsigned int last_drift;
        unsigned long last_jiffies;
        /* If jiffies timer is used */
        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;
}

/* call in cable->lock */
static int loopback_jiffies_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 = DIV_ROUND_UP(tick, dpcm->pcm_bps);
        mod_timer(&dpcm->timer, jiffies + tick);

        return 0;
}

/* call in cable->lock */
static int loopback_snd_timer_start(struct loopback_pcm *dpcm)
{
        struct loopback_cable *cable = dpcm->cable;
        int err;

        /* Loopback device has to use same period as timer card. Therefore
         * wake up for each snd_pcm_period_elapsed() call of timer card.
         */
        err = snd_timer_start(cable->snd_timer.instance, 1);
        if (err < 0) {
                /* do not report error if trying to start but already
                 * running. For example called by opposite substream
                 * of the same cable
                 */
                if (err == -EBUSY)
                        return 0;

                pcm_err(dpcm->substream->pcm,
                        "snd_timer_start(%d,%d,%d) failed with %d",
                        cable->snd_timer.id.card,
                        cable->snd_timer.id.device,
                        cable->snd_timer.id.subdevice,
                        err);
        }

        return err;
}

/* call in cable->lock */
static inline int loopback_jiffies_timer_stop(struct loopback_pcm *dpcm)
{
        del_timer(&dpcm->timer);
        dpcm->timer.expires = 0;

        return 0;
}

/* call in cable->lock */
static int loopback_snd_timer_stop(struct loopback_pcm *dpcm)
{
        struct loopback_cable *cable = dpcm->cable;
        int err;

        /* only stop if both devices (playback and capture) are not running */
        if (cable->running ^ cable->pause)
                return 0;

        err = snd_timer_stop(cable->snd_timer.instance);
        if (err < 0) {
                pcm_err(dpcm->substream->pcm,
                        "snd_timer_stop(%d,%d,%d) failed with %d",
                        cable->snd_timer.id.card,
                        cable->snd_timer.id.device,
                        cable->snd_timer.id.subdevice,
                        err);
        }

        return err;
}

static inline int loopback_jiffies_timer_stop_sync(struct loopback_pcm *dpcm)
{
        del_timer_sync(&dpcm->timer);

        return 0;
}

/* call in loopback->cable_lock */
static int loopback_snd_timer_close_cable(struct loopback_pcm *dpcm)
{
        struct loopback_cable *cable = dpcm->cable;

        /* snd_timer was not opened */
        if (!cable->snd_timer.instance)
                return 0;

        /* will only be called from free_cable() when other stream was
         * already closed. Other stream cannot be reopened as long as
         * loopback->cable_lock is locked. Therefore no need to lock
         * cable->lock;
         */
        snd_timer_close(cable->snd_timer.instance);

        /* wait till drain work has finished if requested */
        cancel_work_sync(&cable->snd_timer.event_work);

        snd_timer_instance_free(cable->snd_timer.instance);
        memset(&cable->snd_timer, 0, sizeof(cable->snd_timer));

        return 0;
}

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 = 0, 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;
                dpcm->last_drift = 0;
                spin_lock(&cable->lock);        
                cable->running |= stream;
                cable->pause &= ~stream;
                err = cable->ops->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;
                err = cable->ops->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;
                err = cable->ops->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;
                err = cable->ops->start(dpcm);
                spin_unlock(&cable->lock);
                if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
                        loopback_active_notify(dpcm);
                break;
        default:
                return -EINVAL;
        }
        return err;
}

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 = 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;

        if (cable->snd_timer.instance) {
                cable->hw.period_bytes_min =
                                frames_to_bytes(runtime, runtime->period_size);
                cable->hw.period_bytes_max = cable->hw.period_bytes_min;
        }

}

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 err, bps, salign;

        if (cable->ops->stop_sync) {
                err = cable->ops->stop_sync(dpcm);
                if (err < 0)
                        return err;
        }

        salign = (snd_pcm_format_physical_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;
        }
}

static inline unsigned int bytepos_delta(struct loopback_pcm *dpcm,
                                         unsigned int jiffies_delta)
{
        unsigned long last_pos;
        unsigned int delta;

        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)
{
        dpcm->buf_pos += delta;
        dpcm->buf_pos %= dpcm->pcm_buffer_size;
}

/* call in cable->lock */
static unsigned int loopback_jiffies_timer_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;
        }

        if (delta_play == 0 && delta_capt == 0)
                goto unlock;
                
        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;

        /* 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;
}

static void loopback_jiffies_timer_function(struct timer_list *t)
{
        struct loopback_pcm *dpcm = from_timer(dpcm, t, timer);
        unsigned long flags;

        spin_lock_irqsave(&dpcm->cable->lock, flags);
        if (loopback_jiffies_timer_pos_update(dpcm->cable) &
                        (1 << dpcm->substream->stream)) {
                loopback_jiffies_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 */
                        snd_pcm_period_elapsed(dpcm->substream);
                        return;
                }
        }
        spin_unlock_irqrestore(&dpcm->cable->lock, flags);
}

/* call in cable->lock */
static int loopback_snd_timer_check_resolution(struct snd_pcm_runtime *runtime,
                                               unsigned long resolution)
{
        if (resolution != runtime->timer_resolution) {
                struct loopback_pcm *dpcm = runtime->private_data;
                struct loopback_cable *cable = dpcm->cable;
                /* Worst case estimation of possible values for resolution
                 * resolution <= (512 * 1024) frames / 8kHz in nsec
                 * resolution <= 65.536.000.000 nsec
                 *
                 * period_size <= 65.536.000.000 nsec / 1000nsec/usec * 192kHz +
                 *  500.000
                 * period_size <= 12.582.912.000.000  <64bit
                 *  / 1.000.000 usec/sec
                 */
                snd_pcm_uframes_t period_size_usec =
                                resolution / 1000 * runtime->rate;
                /* round to nearest sample rate */
                snd_pcm_uframes_t period_size =
                                (period_size_usec + 500 * 1000) / (1000 * 1000);

                pcm_err(dpcm->substream->pcm,
                        "Period size (%lu frames) of loopback device is not corresponding to timer resolution (%lu nsec = %lu frames) of card timer %d,%d,%d. Use period size of %lu frames for loopback device.",
                        runtime->period_size, resolution, period_size,
                        cable->snd_timer.id.card,
                        cable->snd_timer.id.device,
                        cable->snd_timer.id.subdevice,
                        period_size);
                return -EINVAL;
        }
        return 0;
}

static void loopback_snd_timer_period_elapsed(struct loopback_cable *cable,
                                              int event,
                                              unsigned long resolution)
{
        struct loopback_pcm *dpcm_play, *dpcm_capt;
        struct snd_pcm_substream *substream_play, *substream_capt;
        struct snd_pcm_runtime *valid_runtime;
        unsigned int running, elapsed_bytes;
        unsigned long flags;

        spin_lock_irqsave(&cable->lock, flags);
        running = cable->running ^ cable->pause;
        /* no need to do anything if no stream is running */
        if (!running) {
                spin_unlock_irqrestore(&cable->lock, flags);
                return;
        }

        dpcm_play = cable->streams[SNDRV_PCM_STREAM_PLAYBACK];
        dpcm_capt = cable->streams[SNDRV_PCM_STREAM_CAPTURE];

        if (event == SNDRV_TIMER_EVENT_MSTOP) {
                if (!dpcm_play ||
                    dpcm_play->substream->runtime->status->state !=
                                SNDRV_PCM_STATE_DRAINING) {
                        spin_unlock_irqrestore(&cable->lock, flags);
                        return;
                }
        }

        substream_play = (running & (1 << SNDRV_PCM_STREAM_PLAYBACK)) ?
                        dpcm_play->substream : NULL;
        substream_capt = (running & (1 << SNDRV_PCM_STREAM_CAPTURE)) ?
                        dpcm_capt->substream : NULL;
        valid_runtime = (running & (1 << SNDRV_PCM_STREAM_PLAYBACK)) ?
                                dpcm_play->substream->runtime :
                                dpcm_capt->substream->runtime;

        /* resolution is only valid for SNDRV_TIMER_EVENT_TICK events */
        if (event == SNDRV_TIMER_EVENT_TICK) {
                /* The hardware rules guarantee that playback and capture period
                 * are the same. Therefore only one device has to be checked
                 * here.
                 */
                if (loopback_snd_timer_check_resolution(valid_runtime,
                                                        resolution) < 0) {
                        spin_unlock_irqrestore(&cable->lock, flags);
                        if (substream_play)
                                snd_pcm_stop_xrun(substream_play);
                        if (substream_capt)
                                snd_pcm_stop_xrun(substream_capt);
                        return;
                }
        }

        elapsed_bytes = frames_to_bytes(valid_runtime,
                                        valid_runtime->period_size);
        /* The same timer interrupt is used for playback and capture device */
        if ((running & (1 << SNDRV_PCM_STREAM_PLAYBACK)) &&
            (running & (1 << SNDRV_PCM_STREAM_CAPTURE))) {
                copy_play_buf(dpcm_play, dpcm_capt, elapsed_bytes);
                bytepos_finish(dpcm_play, elapsed_bytes);
                bytepos_finish(dpcm_capt, elapsed_bytes);
        } else if (running & (1 << SNDRV_PCM_STREAM_PLAYBACK)) {
                bytepos_finish(dpcm_play, elapsed_bytes);
        } else if (running & (1 << SNDRV_PCM_STREAM_CAPTURE)) {
                clear_capture_buf(dpcm_capt, elapsed_bytes);
                bytepos_finish(dpcm_capt, elapsed_bytes);
        }
        spin_unlock_irqrestore(&cable->lock, flags);

        if (substream_play)
                snd_pcm_period_elapsed(substream_play);
        if (substream_capt)
                snd_pcm_period_elapsed(substream_capt);
}

static void loopback_snd_timer_function(struct snd_timer_instance *timeri,
                                        unsigned long resolution,
                                        unsigned long ticks)
{
        struct loopback_cable *cable = timeri->callback_data;

        loopback_snd_timer_period_elapsed(cable, SNDRV_TIMER_EVENT_TICK,
                                          resolution);
}

static void loopback_snd_timer_work(struct work_struct *work)
{
        struct loopback_cable *cable;

        cable = container_of(work, struct loopback_cable, snd_timer.event_work);
        loopback_snd_timer_period_elapsed(cable, SNDRV_TIMER_EVENT_MSTOP, 0);
}

static void loopback_snd_timer_event(struct snd_timer_instance *timeri,
                                     int event,
                                     struct timespec64 *tstamp,
                                     unsigned long resolution)
{
        /* Do not lock cable->lock here because timer->lock is already hold.
         * There are other functions which first lock cable->lock and than
         * timer->lock e.g.
         * loopback_trigger()
         * spin_lock(&cable->lock)
         * loopback_snd_timer_start()
         * snd_timer_start()
         * spin_lock(&timer->lock)
         * Therefore when using the oposit order of locks here it could result
         * in a deadlock.
         */

        if (event == SNDRV_TIMER_EVENT_MSTOP) {
                struct loopback_cable *cable = timeri->callback_data;

                /* sound card of the timer was stopped. Therefore there will not
                 * be any further timer callbacks. Due to this forward audio
                 * data from here if in draining state. When still in running
                 * state the streaming will be aborted by the usual timeout. It
                 * should not be aborted here because may be the timer sound
                 * card does only a recovery and the timer is back soon.
                 * This work triggers loopback_snd_timer_work()
                 */
                schedule_work(&cable->snd_timer.event_work);
        }
}

static void loopback_jiffies_timer_dpcm_info(struct loopback_pcm *dpcm,
                                             struct snd_info_buffer *buffer)
{
        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 loopback_snd_timer_dpcm_info(struct loopback_pcm *dpcm,
                                         struct snd_info_buffer *buffer)
{
        struct loopback_cable *cable = dpcm->cable;

        snd_iprintf(buffer, "    sound timer:\thw:%d,%d,%d\n",
                    cable->snd_timer.id.card,
                    cable->snd_timer.id.device,
                    cable->snd_timer.id.subdevice);
        snd_iprintf(buffer, "    timer open:\t\t%s\n",
                    (cable->snd_timer.stream == SNDRV_PCM_STREAM_CAPTURE) ?
                            "capture" : "playback");
}

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;

        spin_lock(&dpcm->cable->lock);
        if (dpcm->cable->ops->pos_update)
                dpcm->cable->ops->pos_update(dpcm->cable);
        pos = dpcm->buf_pos;
        spin_unlock(&dpcm->cable->lock);
        return bytes_to_frames(runtime, pos);
}

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_S24_LE | SNDRV_PCM_FMTBIT_S24_BE |
                         SNDRV_PCM_FMTBIT_S24_3LE | SNDRV_PCM_FMTBIT_S24_3BE |
                         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_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 0;
}

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 loopback_pcm *dpcm = rule->private;
        struct loopback_cable *cable = dpcm->cable;
        struct snd_mask m;

        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 rule_rate(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.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 int rule_period_bytes(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.period_bytes_min;
        t.max = cable->hw.period_bytes_max;
        mutex_unlock(&dpcm->loopback->cable_lock);
        t.openmin = 0;
        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 *loopback = substream->private_data;
        int dev = get_cable_index(substream);
        struct loopback_cable *cable;

        cable = loopback->cables[substream->number][dev];
        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 {
                struct loopback_pcm *dpcm = substream->runtime->private_data;

                if (cable->ops && cable->ops->close_cable && dpcm)
                        cable->ops->close_cable(dpcm);
                /* free the cable */
                loopback->cables[substream->number][dev] = NULL;
                kfree(cable);
        }
}

static int loopback_jiffies_timer_open(struct loopback_pcm *dpcm)
{
        timer_setup(&dpcm->timer, loopback_jiffies_timer_function, 0);

        return 0;
}

static const struct loopback_ops loopback_jiffies_timer_ops = {
        .open = loopback_jiffies_timer_open,
        .start = loopback_jiffies_timer_start,
        .stop = loopback_jiffies_timer_stop,
        .stop_sync = loopback_jiffies_timer_stop_sync,
        .close_substream = loopback_jiffies_timer_stop_sync,
        .pos_update = loopback_jiffies_timer_pos_update,
        .dpcm_info = loopback_jiffies_timer_dpcm_info,
};

static int loopback_parse_timer_id(const char *str,
                                   struct snd_timer_id *tid)
{
        /* [<pref>:](<card name>|<card idx>)[{.,}<dev idx>[{.,}<subdev idx>]] */
        const char * const sep_dev = ".,";
        const char * const sep_pref = ":";
        const char *name = str;
        char *sep, save = '\0';
        int card_idx = 0, dev = 0, subdev = 0;
        int err;

        sep = strpbrk(str, sep_pref);
        if (sep)
                name = sep + 1;
        sep = strpbrk(name, sep_dev);
        if (sep) {
                save = *sep;
                *sep = '\0';
        }
        err = kstrtoint(name, 0, &card_idx);
        if (err == -EINVAL) {
                /* Must be the name, not number */
                for (card_idx = 0; card_idx < snd_ecards_limit; card_idx++) {
                        struct snd_card *card = snd_card_ref(card_idx);

                        if (card) {
                                if (!strcmp(card->id, name))
                                        err = 0;
                                snd_card_unref(card);
                        }
                        if (!err)
                                break;
                }
        }
        if (sep) {
                *sep = save;
                if (!err) {
                        char *sep2, save2 = '\0';

                        sep2 = strpbrk(sep + 1, sep_dev);
                        if (sep2) {
                                save2 = *sep2;
                                *sep2 = '\0';
                        }
                        err = kstrtoint(sep + 1, 0, &dev);
                        if (sep2) {
                                *sep2 = save2;
                                if (!err)
                                        err = kstrtoint(sep2 + 1, 0, &subdev);
                        }
                }
        }
        if (!err && tid) {
                tid->card = card_idx;
                tid->device = dev;
                tid->subdevice = subdev;
        }
        return err;
}

/* call in loopback->cable_lock */
static int loopback_snd_timer_open(struct loopback_pcm *dpcm)
{
        int err = 0;
        struct snd_timer_id tid = {
                .dev_class = SNDRV_TIMER_CLASS_PCM,
                .dev_sclass = SNDRV_TIMER_SCLASS_APPLICATION,
        };
        struct snd_timer_instance *timeri;
        struct loopback_cable *cable = dpcm->cable;

        /* check if timer was already opened. It is only opened once
         * per playback and capture subdevice (aka cable).
         */
        if (cable->snd_timer.instance)
                goto exit;

        err = loopback_parse_timer_id(dpcm->loopback->timer_source, &tid);
        if (err < 0) {
                pcm_err(dpcm->substream->pcm,
                        "Parsing timer source \'%s\' failed with %d",
                        dpcm->loopback->timer_source, err);
                goto exit;
        }

        cable->snd_timer.stream = dpcm->substream->stream;
        cable->snd_timer.id = tid;

        timeri = snd_timer_instance_new(dpcm->loopback->card->id);
        if (!timeri) {
                err = -ENOMEM;
                goto exit;
        }
        /* The callback has to be called from another work. If
         * SNDRV_TIMER_IFLG_FAST is specified it will be called from the
         * snd_pcm_period_elapsed() call of the selected sound card.
         * snd_pcm_period_elapsed() helds snd_pcm_stream_lock_irqsave().
         * Due to our callback loopback_snd_timer_function() also calls
         * snd_pcm_period_elapsed() which calls snd_pcm_stream_lock_irqsave().
         * This would end up in a dead lock.
         */
        timeri->flags |= SNDRV_TIMER_IFLG_AUTO;
        timeri->callback = loopback_snd_timer_function;
        timeri->callback_data = (void *)cable;
        timeri->ccallback = loopback_snd_timer_event;

        /* initialise a work used for draining */
        INIT_WORK(&cable->snd_timer.event_work, loopback_snd_timer_work);

        /* The mutex loopback->cable_lock is kept locked.
         * Therefore snd_timer_open() cannot be called a second time
         * by the other device of the same cable.
         * Therefore the following issue cannot happen:
         * [proc1] Call loopback_timer_open() ->
         *         Unlock cable->lock for snd_timer_close/open() call
         * [proc2] Call loopback_timer_open() -> snd_timer_open(),
         *         snd_timer_start()
         * [proc1] Call snd_timer_open() and overwrite running timer
         *         instance
         */
        err = snd_timer_open(timeri, &cable->snd_timer.id, current->pid);
        if (err < 0) {
                pcm_err(dpcm->substream->pcm,
                        "snd_timer_open (%d,%d,%d) failed with %d",
                        cable->snd_timer.id.card,
                        cable->snd_timer.id.device,
                        cable->snd_timer.id.subdevice,
                        err);
                snd_timer_instance_free(timeri);
                goto exit;
        }

        cable->snd_timer.instance = timeri;

exit:
        return err;
}

/* stop_sync() is not required for sound timer because it does not need to be
 * restarted in loopback_prepare() on Xrun recovery
 */
static const struct loopback_ops loopback_snd_timer_ops = {
        .open = loopback_snd_timer_open,
        .start = loopback_snd_timer_start,
        .stop = loopback_snd_timer_stop,
        .close_cable = loopback_snd_timer_close_cable,
        .dpcm_info = loopback_snd_timer_dpcm_info,
};

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 = NULL;
        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;

        cable = loopback->cables[substream->number][dev];
        if (!cable) {
                cable = kzalloc(sizeof(*cable), GFP_KERNEL);
                if (!cable) {
                        err = -ENOMEM;
                        goto unlock;
                }
                spin_lock_init(&cable->lock);
                cable->hw = loopback_pcm_hardware;
                if (loopback->timer_source)
                        cable->ops = &loopback_snd_timer_ops;
                else
                        cable->ops = &loopback_jiffies_timer_ops;
                loopback->cables[substream->number][dev] = cable;
        }
        dpcm->cable = cable;
        runtime->private_data = dpcm;

        if (cable->ops->open) {
                err = cable->ops->open(dpcm);
                if (err < 0)
                        goto unlock;
        }

        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;

        /* In case of sound timer the period time of both devices of the same
         * loop has to be the same.
         * This rule only takes effect if a sound timer was chosen
         */
        if (cable->snd_timer.instance) {
                err = snd_pcm_hw_rule_add(runtime, 0,
                                          SNDRV_PCM_HW_PARAM_PERIOD_BYTES,
                                          rule_period_bytes, dpcm,
                                          SNDRV_PCM_HW_PARAM_PERIOD_BYTES, -1);
                if (err < 0)
                        goto unlock;
        }

        /* loopback_runtime_free() has not to be called if kfree(dpcm) was
         * already called here. Otherwise it will end up with a double free.
         */
        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 *loopback = substream->private_data;
        struct loopback_pcm *dpcm = substream->runtime->private_data;
        int err = 0;

        if (dpcm->cable->ops->close_substream)
                err = dpcm->cable->ops->close_substream(dpcm);
        mutex_lock(&loopback->cable_lock);
        free_cable(substream);
        mutex_unlock(&loopback->cable_lock);
        return err;
}

static const struct snd_pcm_ops loopback_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_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_pcm_ops);
        snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_CAPTURE, &loopback_pcm_ops);
        snd_pcm_set_managed_buffer_all(pcm, SNDRV_DMA_TYPE_VMALLOC, NULL, 0, 0);

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

        loopback->pcm[device] = pcm;
        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);
        
        mutex_lock(&loopback->cable_lock);
        ucontrol->value.integer.value[0] =
                loopback->setup[kcontrol->id.subdevice]
                               [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.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);
        
        mutex_lock(&loopback->cable_lock);
        ucontrol->value.integer.value[0] =
                loopback->setup[kcontrol->id.subdevice]
                               [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.subdevice]
                                [kcontrol->id.device].notify) {
                loopback->setup[kcontrol->id.subdevice]
                        [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.subdevice][kcontrol->id.device ^ 1];
        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 = (__force int)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] =
                (__force int)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);
        
        mutex_lock(&loopback->cable_lock);
        ucontrol->value.integer.value[0] =
                loopback->setup[kcontrol->id.subdevice]
                               [kcontrol->id.device].rate;
        mutex_unlock(&loopback->cable_lock);
        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);
        
        mutex_lock(&loopback->cable_lock);
        ucontrol->value.integer.value[0] =
                loopback->setup[kcontrol->id.subdevice]
                               [kcontrol->id.device].channels;
        mutex_unlock(&loopback->cable_lock);
        return 0;
}

static const 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 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;

                                /* Add the control before copying the id so that
                                 * the numid field of the id is set in the copy.
                                 */
                                err = snd_ctl_add(card, kctl);
                                if (err < 0)
                                        return err;

                                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;
                                }
                        }
                }
        }
        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);
        if (dpcm->cable->ops->dpcm_info)
                dpcm->cable->ops->dpcm_info(dpcm, buffer);
}

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 loopback_cable_proc_new(struct loopback *loopback, int cidx)
{
        char name[32];

        snprintf(name, sizeof(name), "cable#%d", cidx);
        return snd_card_ro_proc_new(loopback->card, name, loopback,
                                    print_cable_info);
}

static void loopback_set_timer_source(struct loopback *loopback,
                                      const char *value)
{
        if (loopback->timer_source) {
                devm_kfree(loopback->card->dev, loopback->timer_source);
                loopback->timer_source = NULL;
        }
        if (value && *value)
                loopback->timer_source = devm_kstrdup(loopback->card->dev,
                                                      value, GFP_KERNEL);
}

static void print_timer_source_info(struct snd_info_entry *entry,
                                    struct snd_info_buffer *buffer)
{
        struct loopback *loopback = entry->private_data;

        mutex_lock(&loopback->cable_lock);
        snd_iprintf(buffer, "%s\n",
                    loopback->timer_source ? loopback->timer_source : "");
        mutex_unlock(&loopback->cable_lock);
}

static void change_timer_source_info(struct snd_info_entry *entry,
                                     struct snd_info_buffer *buffer)
{
        struct loopback *loopback = entry->private_data;
        char line[64];

        mutex_lock(&loopback->cable_lock);
        if (!snd_info_get_line(buffer, line, sizeof(line)))
                loopback_set_timer_source(loopback, strim(line));
        mutex_unlock(&loopback->cable_lock);
}

static int loopback_timer_source_proc_new(struct loopback *loopback)
{
        return snd_card_rw_proc_new(loopback->card, "timer_source", loopback,
                                    print_timer_source_info,
                                    change_timer_source_info);
}

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

        err = snd_devm_card_new(&devptr->dev, 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;
        loopback_set_timer_source(loopback, timer_source[dev]);

        mutex_init(&loopback->cable_lock);

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

#ifdef CONFIG_PM_SLEEP
static int loopback_suspend(struct device *pdev)
{
        struct snd_card *card = dev_get_drvdata(pdev);

        snd_power_change_state(card, SNDRV_CTL_POWER_D3hot);
        return 0;
}
        
static int loopback_resume(struct device *pdev)
{
        struct snd_card *card = dev_get_drvdata(pdev);

        snd_power_change_state(card, SNDRV_CTL_POWER_D0);
        return 0;
}

static SIMPLE_DEV_PM_OPS(loopback_pm, loopback_suspend, loopback_resume);
#define LOOPBACK_PM_OPS &loopback_pm
#else
#define LOOPBACK_PM_OPS NULL
#endif

#define SND_LOOPBACK_DRIVER     "snd_aloop"

static struct platform_driver loopback_driver = {
        .probe          = loopback_probe,
        .driver         = {
                .name   = SND_LOOPBACK_DRIVER,
                .pm     = LOOPBACK_PM_OPS,
        },
};

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)