compress_offload.c

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/*
 *  compress_core.c - compress offload core
 *
 *  Copyright (C) 2011 Intel Corporation
 *  Authors:    Vinod Koul <[email protected]>
 *      Pierre-Louis Bossart <[email protected]>
 *  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; version 2 of the License.
 *
 *  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.
 *
 * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 *
 */
#define FORMAT(fmt) "%s: %d: " fmt, __func__, __LINE__
#define pr_fmt(fmt) KBUILD_MODNAME ": " FORMAT(fmt)

#include <linux/file.h>
#include <linux/fs.h>
#include <linux/list.h>
#include <linux/mm.h>
#include <linux/mutex.h>
#include <linux/poll.h>
#include <linux/slab.h>
#include <linux/sched.h>
#include <linux/uio.h>
#include <linux/uaccess.h>
#include <linux/module.h>
#include <sound/core.h>
#include <sound/initval.h>
#include <sound/compress_params.h>
#include <sound/compress_offload.h>
#include <sound/compress_driver.h>

/* TODO:
 * - add substream support for multiple devices in case of
 *  SND_DYNAMIC_MINORS is not used
 * - Multiple node representation
 *  driver should be able to register multiple nodes
 */

static DEFINE_MUTEX(device_mutex);

struct snd_compr_file {
    unsigned long caps;
    struct snd_compr_stream stream;
};

/*
 * a note on stream states used:
 * we use follwing states in the compressed core
 * SNDRV_PCM_STATE_OPEN: When stream has been opened.
 * SNDRV_PCM_STATE_SETUP: When stream has been initialized. This is done by
 *  calling SNDRV_COMPRESS_SET_PARAMS. running streams will come to this
 *  state at stop by calling SNDRV_COMPRESS_STOP, or at end of drain.
 * SNDRV_PCM_STATE_RUNNING: When stream has been started and is
 *  decoding/encoding and rendering/capturing data.
 * SNDRV_PCM_STATE_DRAINING: When stream is draining current data. This is done
 *  by calling SNDRV_COMPRESS_DRAIN.
 * SNDRV_PCM_STATE_PAUSED: When stream is paused. This is done by calling
 *  SNDRV_COMPRESS_PAUSE. It can be stopped or resumed by calling
 *  SNDRV_COMPRESS_STOP or SNDRV_COMPRESS_RESUME respectively.
 */
static int snd_compr_open(struct inode *inode, struct file *f)
{
    struct snd_compr *compr;
    struct snd_compr_file *data;
    struct snd_compr_runtime *runtime;
    enum snd_compr_direction dirn;
    int maj = imajor(inode);
    int ret;

    if ((f->f_flags & O_ACCMODE) == O_WRONLY)
        dirn = SND_COMPRESS_PLAYBACK;
    else if ((f->f_flags & O_ACCMODE) == O_RDONLY)
        dirn = SND_COMPRESS_CAPTURE;
    else
        return -EINVAL;

    if (maj == snd_major)
        compr = snd_lookup_minor_data(iminor(inode),
                    SNDRV_DEVICE_TYPE_COMPRESS);
    else
        return -EBADFD;

    if (compr == NULL) {
        pr_err("no device data!!!\n");
        return -ENODEV;
    }

    if (dirn != compr->direction) {
        pr_err("this device doesn't support this direction\n");
        snd_card_unref(compr->card);
        return -EINVAL;
    }

    data = kzalloc(sizeof(*data), GFP_KERNEL);
    if (!data) {
        snd_card_unref(compr->card);
        return -ENOMEM;
    }
    data->stream.ops = compr->ops;
    data->stream.direction = dirn;
    data->stream.private_data = compr->private_data;
    data->stream.device = compr;
    runtime = kzalloc(sizeof(*runtime), GFP_KERNEL);
    if (!runtime) {
        kfree(data);
        snd_card_unref(compr->card);
        return -ENOMEM;
    }
    runtime->state = SNDRV_PCM_STATE_OPEN;
    init_waitqueue_head(&runtime->sleep);
    data->stream.runtime = runtime;
    f->private_data = (void *)data;
    mutex_lock(&compr->lock);
    ret = compr->ops->open(&data->stream);
    mutex_unlock(&compr->lock);
    if (ret) {
        kfree(runtime);
        kfree(data);
    }
    snd_card_unref(compr->card);
    return 0;
}

static int snd_compr_free(struct inode *inode, struct file *f)
{
    struct snd_compr_file *data = f->private_data;
    data->stream.ops->free(&data->stream);
    kfree(data->stream.runtime->buffer);
    kfree(data->stream.runtime);
    kfree(data);
    return 0;
}

static void snd_compr_update_tstamp(struct snd_compr_stream *stream,
        struct snd_compr_tstamp *tstamp)
{
    if (!stream->ops->pointer)
        return;
    stream->ops->pointer(stream, tstamp);
    pr_debug("dsp consumed till %d total %d bytes\n",
        tstamp->byte_offset, tstamp->copied_total);
    stream->runtime->hw_pointer = tstamp->byte_offset;
    stream->runtime->total_bytes_transferred = tstamp->copied_total;
}

static size_t snd_compr_calc_avail(struct snd_compr_stream *stream,
        struct snd_compr_avail *avail)
{
    long avail_calc; /*this needs to be signed variable */

    snd_compr_update_tstamp(stream, &avail->tstamp);

    /* FIXME: This needs to be different for capture stream,
       available is # of compressed data, for playback it's
       remainder of buffer */

    if (stream->runtime->total_bytes_available == 0 &&
            stream->runtime->state == SNDRV_PCM_STATE_SETUP) {
        pr_debug("detected init and someone forgot to do a write\n");
        return stream->runtime->buffer_size;
    }
    pr_debug("app wrote %lld, DSP consumed %lld\n",
            stream->runtime->total_bytes_available,
            stream->runtime->total_bytes_transferred);
    if (stream->runtime->total_bytes_available ==
                stream->runtime->total_bytes_transferred) {
        pr_debug("both pointers are same, returning full avail\n");
        return stream->runtime->buffer_size;
    }

    /* FIXME: this routine isn't consistent, in one test we use
     * cumulative values and in the other byte offsets. Do we
     * really need the byte offsets if the cumulative values have
     * been updated? In the PCM interface app_ptr and hw_ptr are
     * already cumulative */

    avail_calc = stream->runtime->buffer_size -
        (stream->runtime->app_pointer - stream->runtime->hw_pointer);
    pr_debug("calc avail as %ld, app_ptr %lld, hw+ptr %lld\n", avail_calc,
            stream->runtime->app_pointer,
            stream->runtime->hw_pointer);
    if (avail_calc >= stream->runtime->buffer_size)
        avail_calc -= stream->runtime->buffer_size;
    pr_debug("ret avail as %ld\n", avail_calc);
    avail->avail = avail_calc;
    return avail_calc;
}

static inline size_t snd_compr_get_avail(struct snd_compr_stream *stream)
{
    struct snd_compr_avail avail;

    return snd_compr_calc_avail(stream, &avail);
}

static int
snd_compr_ioctl_avail(struct snd_compr_stream *stream, unsigned long arg)
{
    struct snd_compr_avail ioctl_avail;
    size_t avail;

    avail = snd_compr_calc_avail(stream, &ioctl_avail);
    ioctl_avail.avail = avail;

    if (copy_to_user((__u64 __user *)arg,
                &ioctl_avail, sizeof(ioctl_avail)))
        return -EFAULT;
    return 0;
}

static int snd_compr_write_data(struct snd_compr_stream *stream,
           const char __user *buf, size_t count)
{
    void *dstn;
    size_t copy;
    struct snd_compr_runtime *runtime = stream->runtime;

    dstn = runtime->buffer + runtime->app_pointer;
    pr_debug("copying %ld at %lld\n",
            (unsigned long)count, runtime->app_pointer);
    if (count < runtime->buffer_size - runtime->app_pointer) {
        if (copy_from_user(dstn, buf, count))
            return -EFAULT;
        runtime->app_pointer += count;
    } else {
        copy = runtime->buffer_size - runtime->app_pointer;
        if (copy_from_user(dstn, buf, copy))
            return -EFAULT;
        if (copy_from_user(runtime->buffer, buf + copy, count - copy))
            return -EFAULT;
        runtime->app_pointer = count - copy;
    }
    /* if DSP cares, let it know data has been written */
    if (stream->ops->ack)
        stream->ops->ack(stream, count);
    return count;
}

static ssize_t snd_compr_write(struct file *f, const char __user *buf,
        size_t count, loff_t *offset)
{
    struct snd_compr_file *data = f->private_data;
    struct snd_compr_stream *stream;
    size_t avail;
    int retval;

    if (snd_BUG_ON(!data))
        return -EFAULT;

    stream = &data->stream;
    mutex_lock(&stream->device->lock);
    /* write is allowed when stream is running or has been steup */
    if (stream->runtime->state != SNDRV_PCM_STATE_SETUP &&
            stream->runtime->state != SNDRV_PCM_STATE_RUNNING) {
        mutex_unlock(&stream->device->lock);
        return -EBADFD;
    }

    avail = snd_compr_get_avail(stream);
    pr_debug("avail returned %ld\n", (unsigned long)avail);
    /* calculate how much we can write to buffer */
    if (avail > count)
        avail = count;

    if (stream->ops->copy)
        retval = stream->ops->copy(stream, buf, avail);
    else
        retval = snd_compr_write_data(stream, buf, avail);
    if (retval > 0)
        stream->runtime->total_bytes_available += retval;

    /* while initiating the stream, write should be called before START
     * call, so in setup move state */
    if (stream->runtime->state == SNDRV_PCM_STATE_SETUP) {
        stream->runtime->state = SNDRV_PCM_STATE_PREPARED;
        pr_debug("stream prepared, Houston we are good to go\n");
    }

    mutex_unlock(&stream->device->lock);
    return retval;
}


static ssize_t snd_compr_read(struct file *f, char __user *buf,
        size_t count, loff_t *offset)
{
    return -ENXIO;
}

static int snd_compr_mmap(struct file *f, struct vm_area_struct *vma)
{
    return -ENXIO;
}

static inline int snd_compr_get_poll(struct snd_compr_stream *stream)
{
    if (stream->direction == SND_COMPRESS_PLAYBACK)
        return POLLOUT | POLLWRNORM;
    else
        return POLLIN | POLLRDNORM;
}

static unsigned int snd_compr_poll(struct file *f, poll_table *wait)
{
    struct snd_compr_file *data = f->private_data;
    struct snd_compr_stream *stream;
    size_t avail;
    int retval = 0;

    if (snd_BUG_ON(!data))
        return -EFAULT;
    stream = &data->stream;
    if (snd_BUG_ON(!stream))
        return -EFAULT;

    mutex_lock(&stream->device->lock);
    if (stream->runtime->state == SNDRV_PCM_STATE_PAUSED ||
            stream->runtime->state == SNDRV_PCM_STATE_OPEN) {
        retval = -EBADFD;
        goto out;
    }
    poll_wait(f, &stream->runtime->sleep, wait);

    avail = snd_compr_get_avail(stream);
    pr_debug("avail is %ld\n", (unsigned long)avail);
    /* check if we have at least one fragment to fill */
    switch (stream->runtime->state) {
    case SNDRV_PCM_STATE_DRAINING:
        /* stream has been woken up after drain is complete
         * draining done so set stream state to stopped
         */
        retval = snd_compr_get_poll(stream);
        stream->runtime->state = SNDRV_PCM_STATE_SETUP;
        break;
    case SNDRV_PCM_STATE_RUNNING:
    case SNDRV_PCM_STATE_PREPARED:
    case SNDRV_PCM_STATE_PAUSED:
        if (avail >= stream->runtime->fragment_size)
            retval = snd_compr_get_poll(stream);
        break;
    default:
        if (stream->direction == SND_COMPRESS_PLAYBACK)
            retval = POLLOUT | POLLWRNORM | POLLERR;
        else
            retval = POLLIN | POLLRDNORM | POLLERR;
        break;
    }
out:
    mutex_unlock(&stream->device->lock);
    return retval;
}

static int
snd_compr_get_caps(struct snd_compr_stream *stream, unsigned long arg)
{
    int retval;
    struct snd_compr_caps caps;

    if (!stream->ops->get_caps)
        return -ENXIO;

    retval = stream->ops->get_caps(stream, &caps);
    if (retval)
        goto out;
    if (copy_to_user((void __user *)arg, &caps, sizeof(caps)))
        retval = -EFAULT;
out:
    return retval;
}

static int
snd_compr_get_codec_caps(struct snd_compr_stream *stream, unsigned long arg)
{
    int retval;
    struct snd_compr_codec_caps *caps;

    if (!stream->ops->get_codec_caps)
        return -ENXIO;

    caps = kmalloc(sizeof(*caps), GFP_KERNEL);
    if (!caps)
        return -ENOMEM;

    retval = stream->ops->get_codec_caps(stream, caps);
    if (retval)
        goto out;
    if (copy_to_user((void __user *)arg, caps, sizeof(*caps)))
        retval = -EFAULT;

out:
    kfree(caps);
    return retval;
}

/* revisit this with snd_pcm_preallocate_xxx */
static int snd_compr_allocate_buffer(struct snd_compr_stream *stream,
        struct snd_compr_params *params)
{
    unsigned int buffer_size;
    void *buffer;

    buffer_size = params->buffer.fragment_size * params->buffer.fragments;
    if (stream->ops->copy) {
        buffer = NULL;
        /* if copy is defined the driver will be required to copy
         * the data from core
         */
    } else {
        buffer = kmalloc(buffer_size, GFP_KERNEL);
        if (!buffer)
            return -ENOMEM;
    }
    stream->runtime->fragment_size = params->buffer.fragment_size;
    stream->runtime->fragments = params->buffer.fragments;
    stream->runtime->buffer = buffer;
    stream->runtime->buffer_size = buffer_size;
    return 0;
}

static int snd_compress_check_input(struct snd_compr_params *params)
{
    /* first let's check the buffer parameter's */
    if (params->buffer.fragment_size == 0 ||
            params->buffer.fragments > SIZE_MAX / params->buffer.fragment_size)
        return -EINVAL;

    /* now codec parameters */
    if (params->codec.id == 0 || params->codec.id > SND_AUDIOCODEC_MAX)
        return -EINVAL;

    if (params->codec.ch_in == 0 || params->codec.ch_out == 0)
        return -EINVAL;

    if (!(params->codec.sample_rate & SNDRV_PCM_RATE_8000_192000))
        return -EINVAL;

    return 0;
}

static int
snd_compr_set_params(struct snd_compr_stream *stream, unsigned long arg)
{
    struct snd_compr_params *params;
    int retval;

    if (stream->runtime->state == SNDRV_PCM_STATE_OPEN) {
        /*
         * we should allow parameter change only when stream has been
         * opened not in other cases
         */
        params = kmalloc(sizeof(*params), GFP_KERNEL);
        if (!params)
            return -ENOMEM;
        if (copy_from_user(params, (void __user *)arg, sizeof(*params))) {
            retval = -EFAULT;
            goto out;
        }

        retval = snd_compress_check_input(params);
        if (retval)
            goto out;

        retval = snd_compr_allocate_buffer(stream, params);
        if (retval) {
            retval = -ENOMEM;
            goto out;
        }

        retval = stream->ops->set_params(stream, params);
        if (retval)
            goto out;
        stream->runtime->state = SNDRV_PCM_STATE_SETUP;
    } else {
        return -EPERM;
    }
out:
    kfree(params);
    return retval;
}

static int
snd_compr_get_params(struct snd_compr_stream *stream, unsigned long arg)
{
    struct snd_codec *params;
    int retval;

    if (!stream->ops->get_params)
        return -EBADFD;

    params = kmalloc(sizeof(*params), GFP_KERNEL);
    if (!params)
        return -ENOMEM;
    retval = stream->ops->get_params(stream, params);
    if (retval)
        goto out;
    if (copy_to_user((char __user *)arg, params, sizeof(*params)))
        retval = -EFAULT;

out:
    kfree(params);
    return retval;
}

static inline int
snd_compr_tstamp(struct snd_compr_stream *stream, unsigned long arg)
{
    struct snd_compr_tstamp tstamp;

    snd_compr_update_tstamp(stream, &tstamp);
    return copy_to_user((struct snd_compr_tstamp __user *)arg,
        &tstamp, sizeof(tstamp)) ? -EFAULT : 0;
}

static int snd_compr_pause(struct snd_compr_stream *stream)
{
    int retval;

    if (stream->runtime->state != SNDRV_PCM_STATE_RUNNING)
        return -EPERM;
    retval = stream->ops->trigger(stream, SNDRV_PCM_TRIGGER_PAUSE_PUSH);
    if (!retval)
        stream->runtime->state = SNDRV_PCM_STATE_PAUSED;
    return retval;
}

static int snd_compr_resume(struct snd_compr_stream *stream)
{
    int retval;

    if (stream->runtime->state != SNDRV_PCM_STATE_PAUSED)
        return -EPERM;
    retval = stream->ops->trigger(stream, SNDRV_PCM_TRIGGER_PAUSE_RELEASE);
    if (!retval)
        stream->runtime->state = SNDRV_PCM_STATE_RUNNING;
    return retval;
}

static int snd_compr_start(struct snd_compr_stream *stream)
{
    int retval;

    if (stream->runtime->state != SNDRV_PCM_STATE_PREPARED)
        return -EPERM;
    retval = stream->ops->trigger(stream, SNDRV_PCM_TRIGGER_START);
    if (!retval)
        stream->runtime->state = SNDRV_PCM_STATE_RUNNING;
    return retval;
}

static int snd_compr_stop(struct snd_compr_stream *stream)
{
    int retval;

    if (stream->runtime->state == SNDRV_PCM_STATE_PREPARED ||
            stream->runtime->state == SNDRV_PCM_STATE_SETUP)
        return -EPERM;
    retval = stream->ops->trigger(stream, SNDRV_PCM_TRIGGER_STOP);
    if (!retval) {
        stream->runtime->state = SNDRV_PCM_STATE_SETUP;
        wake_up(&stream->runtime->sleep);
        stream->runtime->hw_pointer = 0;
        stream->runtime->app_pointer = 0;
        stream->runtime->total_bytes_available = 0;
        stream->runtime->total_bytes_transferred = 0;
    }
    return retval;
}

static int snd_compr_drain(struct snd_compr_stream *stream)
{
    int retval;

    if (stream->runtime->state == SNDRV_PCM_STATE_PREPARED ||
            stream->runtime->state == SNDRV_PCM_STATE_SETUP)
        return -EPERM;
    retval = stream->ops->trigger(stream, SND_COMPR_TRIGGER_DRAIN);
    if (!retval) {
        stream->runtime->state = SNDRV_PCM_STATE_DRAINING;
        wake_up(&stream->runtime->sleep);
    }
    return retval;
}

static long snd_compr_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
{
    struct snd_compr_file *data = f->private_data;
    struct snd_compr_stream *stream;
    int retval = -ENOTTY;

    if (snd_BUG_ON(!data))
        return -EFAULT;
    stream = &data->stream;
    if (snd_BUG_ON(!stream))
        return -EFAULT;
    mutex_lock(&stream->device->lock);
    switch (_IOC_NR(cmd)) {
    case _IOC_NR(SNDRV_COMPRESS_IOCTL_VERSION):
        put_user(SNDRV_COMPRESS_VERSION,
                (int __user *)arg) ? -EFAULT : 0;
        break;
    case _IOC_NR(SNDRV_COMPRESS_GET_CAPS):
        retval = snd_compr_get_caps(stream, arg);
        break;
    case _IOC_NR(SNDRV_COMPRESS_GET_CODEC_CAPS):
        retval = snd_compr_get_codec_caps(stream, arg);
        break;
    case _IOC_NR(SNDRV_COMPRESS_SET_PARAMS):
        retval = snd_compr_set_params(stream, arg);
        break;
    case _IOC_NR(SNDRV_COMPRESS_GET_PARAMS):
        retval = snd_compr_get_params(stream, arg);
        break;
    case _IOC_NR(SNDRV_COMPRESS_TSTAMP):
        retval = snd_compr_tstamp(stream, arg);
        break;
    case _IOC_NR(SNDRV_COMPRESS_AVAIL):
        retval = snd_compr_ioctl_avail(stream, arg);
        break;
    case _IOC_NR(SNDRV_COMPRESS_PAUSE):
        retval = snd_compr_pause(stream);
        break;
    case _IOC_NR(SNDRV_COMPRESS_RESUME):
        retval = snd_compr_resume(stream);
        break;
    case _IOC_NR(SNDRV_COMPRESS_START):
        retval = snd_compr_start(stream);
        break;
    case _IOC_NR(SNDRV_COMPRESS_STOP):
        retval = snd_compr_stop(stream);
        break;
    case _IOC_NR(SNDRV_COMPRESS_DRAIN):
        retval = snd_compr_drain(stream);
        break;
    }
    mutex_unlock(&stream->device->lock);
    return retval;
}

static const struct file_operations snd_compr_file_ops = {
        .owner =    THIS_MODULE,
        .open =     snd_compr_open,
        .release =  snd_compr_free,
        .write =    snd_compr_write,
        .read =     snd_compr_read,
        .unlocked_ioctl = snd_compr_ioctl,
        .mmap =     snd_compr_mmap,
        .poll =     snd_compr_poll,
};

static int snd_compress_dev_register(struct snd_device *device)
{
    int ret = -EINVAL;
    char str[16];
    struct snd_compr *compr;

    if (snd_BUG_ON(!device || !device->device_data))
        return -EBADFD;
    compr = device->device_data;

    sprintf(str, "comprC%iD%i", compr->card->number, compr->device);
    pr_debug("reg %s for device %s, direction %d\n", str, compr->name,
            compr->direction);
    /* register compressed device */
    ret = snd_register_device(SNDRV_DEVICE_TYPE_COMPRESS, compr->card,
            compr->device, &snd_compr_file_ops, compr, str);
    if (ret < 0) {
        pr_err("snd_register_device failed\n %d", ret);
        return ret;
    }
    return ret;

}

static int snd_compress_dev_disconnect(struct snd_device *device)
{
    struct snd_compr *compr;

    compr = device->device_data;
    snd_unregister_device(compr->direction, compr->card, compr->device);
    return 0;
}

/*
 * snd_compress_new: create new compress device
 * @card: sound card pointer
 * @device: device number
 * @dirn: device direction, should be of type enum snd_compr_direction
 * @compr: compress device pointer
 */
int snd_compress_new(struct snd_card *card, int device,
            int dirn, struct snd_compr *compr)
{
    static struct snd_device_ops ops = {
        .dev_free = NULL,
        .dev_register = snd_compress_dev_register,
        .dev_disconnect = snd_compress_dev_disconnect,
    };

    compr->card = card;
    compr->device = device;
    compr->direction = dirn;
    return snd_device_new(card, SNDRV_DEV_COMPRESS, compr, &ops);
}
EXPORT_SYMBOL_GPL(snd_compress_new);

static int snd_compress_add_device(struct snd_compr *device)
{
    int ret;

    if (!device->card)
        return -EINVAL;

    /* register the card */
    ret = snd_card_register(device->card);
    if (ret)
        goto out;
    return 0;

out:
    pr_err("failed with %d\n", ret);
    return ret;

}

static int snd_compress_remove_device(struct snd_compr *device)
{
    return snd_card_free(device->card);
}

int snd_compress_register(struct snd_compr *device)
{
    int retval;

    if (device->name == NULL || device->dev == NULL || device->ops == NULL)
        return -EINVAL;

    pr_debug("Registering compressed device %s\n", device->name);
    if (snd_BUG_ON(!device->ops->open))
        return -EINVAL;
    if (snd_BUG_ON(!device->ops->free))
        return -EINVAL;
    if (snd_BUG_ON(!device->ops->set_params))
        return -EINVAL;
    if (snd_BUG_ON(!device->ops->trigger))
        return -EINVAL;

    mutex_init(&device->lock);

    /* register a compressed card */
    mutex_lock(&device_mutex);
    retval = snd_compress_add_device(device);
    mutex_unlock(&device_mutex);
    return retval;
}
EXPORT_SYMBOL_GPL(snd_compress_register);

int snd_compress_deregister(struct snd_compr *device)
{
    pr_debug("Removing compressed device %s\n", device->name);
    mutex_lock(&device_mutex);
    snd_compress_remove_device(device);
    mutex_unlock(&device_mutex);
    return 0;
}
EXPORT_SYMBOL_GPL(snd_compress_deregister);

static int __init snd_compress_init(void)
{
    return 0;
}

static void __exit snd_compress_exit(void)
{
}

module_init(snd_compress_init);
module_exit(snd_compress_exit);

MODULE_DESCRIPTION("ALSA Compressed offload framework");
MODULE_AUTHOR("Vinod Koul <[email protected]>");
MODULE_LICENSE("GPL v2");