#include <linux/slab.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/device.h>
#include <linux/workqueue.h>
#include <linux/kfifo.h>
#include <linux/mutex.h>
#include <linux/iio/kfifo_buf.h>
#include <linux/sched.h>
#include <linux/poll.h>

struct iio_kfifo {
        struct iio_buffer buffer;
        struct kfifo kf;
        struct mutex user_lock;
        int update_needed;
};

#define iio_to_kfifo(r) container_of(r, struct iio_kfifo, buffer)

static inline int __iio_allocate_kfifo(struct iio_kfifo *buf,
                                int bytes_per_datum, int length)
{
        if ((length == 0) || (bytes_per_datum == 0))
                return -EINVAL;

        return __kfifo_alloc((struct __kfifo *)&buf->kf, length,
                             bytes_per_datum, GFP_KERNEL);
}

static int iio_request_update_kfifo(struct iio_buffer *r)
{
        int ret = 0;
        struct iio_kfifo *buf = iio_to_kfifo(r);

        mutex_lock(&buf->user_lock);
        if (buf->update_needed) {
                kfifo_free(&buf->kf);
                ret = __iio_allocate_kfifo(buf, buf->buffer.bytes_per_datum,
                                   buf->buffer.length);
                if (ret >= 0)
                        buf->update_needed = false;
        } else {
                kfifo_reset_out(&buf->kf);
        }
        mutex_unlock(&buf->user_lock);

        return ret;
}

static int iio_mark_update_needed_kfifo(struct iio_buffer *r)
{
        struct iio_kfifo *kf = iio_to_kfifo(r);
        kf->update_needed = true;
        return 0;
}

static int iio_set_bytes_per_datum_kfifo(struct iio_buffer *r, size_t bpd)
{
        if (r->bytes_per_datum != bpd) {
                r->bytes_per_datum = bpd;
                iio_mark_update_needed_kfifo(r);
        }
        return 0;
}

static int iio_set_length_kfifo(struct iio_buffer *r, int length)
{
        /* Avoid an invalid state */
        if (length < 2)
                length = 2;
        if (r->length != length) {
                r->length = length;
                iio_mark_update_needed_kfifo(r);
        }
        return 0;
}

static int iio_store_to_kfifo(struct iio_buffer *r,
                              const void *data)
{
        int ret;
        struct iio_kfifo *kf = iio_to_kfifo(r);
        ret = kfifo_in(&kf->kf, data, 1);
        if (ret != 1)
                return -EBUSY;
        return 0;
}

static int iio_read_first_n_kfifo(struct iio_buffer *r,
                           size_t n, char __user *buf)
{
        int ret, copied;
        struct iio_kfifo *kf = iio_to_kfifo(r);

        if (mutex_lock_interruptible(&kf->user_lock))
                return -ERESTARTSYS;

        if (!kfifo_initialized(&kf->kf) || n < kfifo_esize(&kf->kf))
                ret = -EINVAL;
        else
                ret = kfifo_to_user(&kf->kf, buf, n, &copied);
        mutex_unlock(&kf->user_lock);
        if (ret < 0)
                return ret;

        return copied;
}

static size_t iio_kfifo_buf_data_available(struct iio_buffer *r)
{
        struct iio_kfifo *kf = iio_to_kfifo(r);
        size_t samples;

        mutex_lock(&kf->user_lock);
        samples = kfifo_len(&kf->kf);
        mutex_unlock(&kf->user_lock);

        return samples;
}

static void iio_kfifo_buffer_release(struct iio_buffer *buffer)
{
        struct iio_kfifo *kf = iio_to_kfifo(buffer);

        mutex_destroy(&kf->user_lock);
        kfifo_free(&kf->kf);
        kfree(kf);
}

static const struct iio_buffer_access_funcs kfifo_access_funcs = {
        .store_to = &iio_store_to_kfifo,
        .read_first_n = &iio_read_first_n_kfifo,
        .data_available = iio_kfifo_buf_data_available,
        .request_update = &iio_request_update_kfifo,
        .set_bytes_per_datum = &iio_set_bytes_per_datum_kfifo,
        .set_length = &iio_set_length_kfifo,
        .release = &iio_kfifo_buffer_release,

        .modes = INDIO_BUFFER_SOFTWARE | INDIO_BUFFER_TRIGGERED,
};

struct iio_buffer *iio_kfifo_allocate(void)
{
        struct iio_kfifo *kf;

        kf = kzalloc(sizeof(*kf), GFP_KERNEL);
        if (!kf)
                return NULL;

        kf->update_needed = true;
        iio_buffer_init(&kf->buffer);
        kf->buffer.access = &kfifo_access_funcs;
        kf->buffer.length = 2;
        mutex_init(&kf->user_lock);

        return &kf->buffer;
}
EXPORT_SYMBOL(iio_kfifo_allocate);

void iio_kfifo_free(struct iio_buffer *r)
{
        iio_buffer_put(r);
}
EXPORT_SYMBOL(iio_kfifo_free);

static void devm_iio_kfifo_release(struct device *dev, void *res)
{
        iio_kfifo_free(*(struct iio_buffer **)res);
}

static int devm_iio_kfifo_match(struct device *dev, void *res, void *data)
{
        struct iio_buffer **r = res;

        if (WARN_ON(!r || !*r))
                return 0;

        return *r == data;
}

/**
 * devm_iio_fifo_allocate - Resource-managed iio_kfifo_allocate()
 * @dev:                Device to allocate kfifo buffer for
 *
 * RETURNS:
 * Pointer to allocated iio_buffer on success, NULL on failure.
 */
struct iio_buffer *devm_iio_kfifo_allocate(struct device *dev)
{
        struct iio_buffer **ptr, *r;

        ptr = devres_alloc(devm_iio_kfifo_release, sizeof(*ptr), GFP_KERNEL);
        if (!ptr)
                return NULL;

        r = iio_kfifo_allocate();
        if (r) {
                *ptr = r;
                devres_add(dev, ptr);
        } else {
                devres_free(ptr);
        }

        return r;
}
EXPORT_SYMBOL(devm_iio_kfifo_allocate);

/**
 * devm_iio_fifo_free - Resource-managed iio_kfifo_free()
 * @dev:                Device the buffer belongs to
 * @r:                  The buffer associated with the device
 */
void devm_iio_kfifo_free(struct device *dev, struct iio_buffer *r)
{
        WARN_ON(devres_release(dev, devm_iio_kfifo_release,
                               devm_iio_kfifo_match, r));
}
EXPORT_SYMBOL(devm_iio_kfifo_free);

MODULE_LICENSE("GPL");