/* The industrial I/O core
 *
 * Copyright (c) 2008 Jonathan Cameron
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 as published by
 * the Free Software Foundation.
 *
 * Handling of buffer allocation / resizing.
 *
 *
 * Things to look at here.
 * - Better memory allocation techniques?
 * - Alternative access techniques?
 */
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/device.h>
#include <linux/fs.h>
#include <linux/cdev.h>
#include <linux/slab.h>
#include <linux/poll.h>
#include <linux/sched/signal.h>

#include <linux/iio/iio.h>
#include "iio_core.h"
#include <linux/iio/sysfs.h>
#include <linux/iio/buffer.h>
#include <linux/iio/buffer_impl.h>

static const char * const iio_endian_prefix[] = {
        [IIO_BE] = "be",
        [IIO_LE] = "le",
};

static bool iio_buffer_is_active(struct iio_buffer *buf)
{
        return !list_empty(&buf->buffer_list);
}

static size_t iio_buffer_data_available(struct iio_buffer *buf)
{
        return buf->access->data_available(buf);
}

static int iio_buffer_flush_hwfifo(struct iio_dev *indio_dev,
                                   struct iio_buffer *buf, size_t required)
{
        if (!indio_dev->info->hwfifo_flush_to_buffer)
                return -ENODEV;

        return indio_dev->info->hwfifo_flush_to_buffer(indio_dev, required);
}

static bool iio_buffer_ready(struct iio_dev *indio_dev, struct iio_buffer *buf,
                             size_t to_wait, int to_flush)
{
        size_t avail;
        int flushed = 0;

        /* wakeup if the device was unregistered */
        if (!indio_dev->info)
                return true;

        /* drain the buffer if it was disabled */
        if (!iio_buffer_is_active(buf)) {
                to_wait = min_t(size_t, to_wait, 1);
                to_flush = 0;
        }

        avail = iio_buffer_data_available(buf);

        if (avail >= to_wait) {
                /* force a flush for non-blocking reads */
                if (!to_wait && avail < to_flush)
                        iio_buffer_flush_hwfifo(indio_dev, buf,
                                                to_flush - avail);
                return true;
        }

        if (to_flush)
                flushed = iio_buffer_flush_hwfifo(indio_dev, buf,
                                                  to_wait - avail);
        if (flushed <= 0)
                return false;

        if (avail + flushed >= to_wait)
                return true;

        return false;
}

/**
 * iio_buffer_read_first_n_outer() - chrdev read for buffer access
 * @filp:       File structure pointer for the char device
 * @buf:        Destination buffer for iio buffer read
 * @n:          First n bytes to read
 * @f_ps:       Long offset provided by the user as a seek position
 *
 * This function relies on all buffer implementations having an
 * iio_buffer as their first element.
 *
 * Return: negative values corresponding to error codes or ret != 0
 *         for ending the reading activity
 **/
ssize_t iio_buffer_read_first_n_outer(struct file *filp, char __user *buf,
                                      size_t n, loff_t *f_ps)
{
        struct iio_dev *indio_dev = filp->private_data;
        struct iio_buffer *rb = indio_dev->buffer;
        DEFINE_WAIT_FUNC(wait, woken_wake_function);
        size_t datum_size;
        size_t to_wait;
        int ret = 0;

        if (!indio_dev->info)
                return -ENODEV;

        if (!rb || !rb->access->read_first_n)
                return -EINVAL;

        datum_size = rb->bytes_per_datum;

        /*
         * If datum_size is 0 there will never be anything to read from the
         * buffer, so signal end of file now.
         */
        if (!datum_size)
                return 0;

        if (filp->f_flags & O_NONBLOCK)
                to_wait = 0;
        else
                to_wait = min_t(size_t, n / datum_size, rb->watermark);

        add_wait_queue(&rb->pollq, &wait);
        do {
                if (!indio_dev->info) {
                        ret = -ENODEV;
                        break;
                }

                if (!iio_buffer_ready(indio_dev, rb, to_wait, n / datum_size)) {
                        if (signal_pending(current)) {
                                ret = -ERESTARTSYS;
                                break;
                        }

                        wait_woken(&wait, TASK_INTERRUPTIBLE,
                                   MAX_SCHEDULE_TIMEOUT);
                        continue;
                }

                ret = rb->access->read_first_n(rb, n, buf);
                if (ret == 0 && (filp->f_flags & O_NONBLOCK))
                        ret = -EAGAIN;
        } while (ret == 0);
        remove_wait_queue(&rb->pollq, &wait);

        return ret;
}

/**
 * iio_buffer_poll() - poll the buffer to find out if it has data
 * @filp:       File structure pointer for device access
 * @wait:       Poll table structure pointer for which the driver adds
 *              a wait queue
 *
 * Return: (POLLIN | POLLRDNORM) if data is available for reading
 *         or 0 for other cases
 */
unsigned int iio_buffer_poll(struct file *filp,
                             struct poll_table_struct *wait)
{
        struct iio_dev *indio_dev = filp->private_data;
        struct iio_buffer *rb = indio_dev->buffer;

        if (!indio_dev->info)
                return 0;

        poll_wait(filp, &rb->pollq, wait);
        if (iio_buffer_ready(indio_dev, rb, rb->watermark, 0))
                return POLLIN | POLLRDNORM;
        return 0;
}

/**
 * iio_buffer_wakeup_poll - Wakes up the buffer waitqueue
 * @indio_dev: The IIO device
 *
 * Wakes up the event waitqueue used for poll(). Should usually
 * be called when the device is unregistered.
 */
void iio_buffer_wakeup_poll(struct iio_dev *indio_dev)
{
        if (!indio_dev->buffer)
                return;

        wake_up(&indio_dev->buffer->pollq);
}

void iio_buffer_init(struct iio_buffer *buffer)
{
        INIT_LIST_HEAD(&buffer->demux_list);
        INIT_LIST_HEAD(&buffer->buffer_list);
        init_waitqueue_head(&buffer->pollq);
        kref_init(&buffer->ref);
        if (!buffer->watermark)
                buffer->watermark = 1;
}
EXPORT_SYMBOL(iio_buffer_init);

/**
 * iio_buffer_set_attrs - Set buffer specific attributes
 * @buffer: The buffer for which we are setting attributes
 * @attrs: Pointer to a null terminated list of pointers to attributes
 */
void iio_buffer_set_attrs(struct iio_buffer *buffer,
                         const struct attribute **attrs)
{
        buffer->attrs = attrs;
}
EXPORT_SYMBOL_GPL(iio_buffer_set_attrs);

static ssize_t iio_show_scan_index(struct device *dev,
                                   struct device_attribute *attr,
                                   char *buf)
{
        return sprintf(buf, "%u\n", to_iio_dev_attr(attr)->c->scan_index);
}

static ssize_t iio_show_fixed_type(struct device *dev,
                                   struct device_attribute *attr,
                                   char *buf)
{
        struct iio_dev_attr *this_attr = to_iio_dev_attr(attr);
        u8 type = this_attr->c->scan_type.endianness;

        if (type == IIO_CPU) {
#ifdef __LITTLE_ENDIAN
                type = IIO_LE;
#else
                type = IIO_BE;
#endif
        }
        if (this_attr->c->scan_type.repeat > 1)
                return sprintf(buf, "%s:%c%d/%dX%d>>%u\n",
                       iio_endian_prefix[type],
                       this_attr->c->scan_type.sign,
                       this_attr->c->scan_type.realbits,
                       this_attr->c->scan_type.storagebits,
                       this_attr->c->scan_type.repeat,
                       this_attr->c->scan_type.shift);
                else
                        return sprintf(buf, "%s:%c%d/%d>>%u\n",
                       iio_endian_prefix[type],
                       this_attr->c->scan_type.sign,
                       this_attr->c->scan_type.realbits,
                       this_attr->c->scan_type.storagebits,
                       this_attr->c->scan_type.shift);
}

static ssize_t iio_scan_el_show(struct device *dev,
                                struct device_attribute *attr,
                                char *buf)
{
        int ret;
        struct iio_dev *indio_dev = dev_to_iio_dev(dev);

        /* Ensure ret is 0 or 1. */
        ret = !!test_bit(to_iio_dev_attr(attr)->address,
                       indio_dev->buffer->scan_mask);

        return sprintf(buf, "%d\n", ret);
}

/* Note NULL used as error indicator as it doesn't make sense. */
static const unsigned long *iio_scan_mask_match(const unsigned long *av_masks,
                                          unsigned int masklength,
                                          const unsigned long *mask,
                                          bool strict)
{
        if (bitmap_empty(mask, masklength))
                return NULL;
        while (*av_masks) {
                if (strict) {
                        if (bitmap_equal(mask, av_masks, masklength))
                                return av_masks;
                } else {
                        if (bitmap_subset(mask, av_masks, masklength))
                                return av_masks;
                }
                av_masks += BITS_TO_LONGS(masklength);
        }
        return NULL;
}

static bool iio_validate_scan_mask(struct iio_dev *indio_dev,
        const unsigned long *mask)
{
        if (!indio_dev->setup_ops->validate_scan_mask)
                return true;

        return indio_dev->setup_ops->validate_scan_mask(indio_dev, mask);
}

/**
 * iio_scan_mask_set() - set particular bit in the scan mask
 * @indio_dev: the iio device
 * @buffer: the buffer whose scan mask we are interested in
 * @bit: the bit to be set.
 *
 * Note that at this point we have no way of knowing what other
 * buffers might request, hence this code only verifies that the
 * individual buffers request is plausible.
 */
static int iio_scan_mask_set(struct iio_dev *indio_dev,
                      struct iio_buffer *buffer, int bit)
{
        const unsigned long *mask;
        unsigned long *trialmask;

        trialmask = kmalloc_array(BITS_TO_LONGS(indio_dev->masklength),
                                  sizeof(*trialmask),
                                  GFP_KERNEL);
        if (trialmask == NULL)
                return -ENOMEM;
        if (!indio_dev->masklength) {
                WARN(1, "Trying to set scanmask prior to registering buffer\n");
                goto err_invalid_mask;
        }
        bitmap_copy(trialmask, buffer->scan_mask, indio_dev->masklength);
        set_bit(bit, trialmask);

        if (!iio_validate_scan_mask(indio_dev, trialmask))
                goto err_invalid_mask;

        if (indio_dev->available_scan_masks) {
                mask = iio_scan_mask_match(indio_dev->available_scan_masks,
                                           indio_dev->masklength,
                                           trialmask, false);
                if (!mask)
                        goto err_invalid_mask;
        }
        bitmap_copy(buffer->scan_mask, trialmask, indio_dev->masklength);

        kfree(trialmask);

        return 0;

err_invalid_mask:
        kfree(trialmask);
        return -EINVAL;
}

static int iio_scan_mask_clear(struct iio_buffer *buffer, int bit)
{
        clear_bit(bit, buffer->scan_mask);
        return 0;
}

static int iio_scan_mask_query(struct iio_dev *indio_dev,
                               struct iio_buffer *buffer, int bit)
{
        if (bit > indio_dev->masklength)
                return -EINVAL;

        if (!buffer->scan_mask)
                return 0;

        /* Ensure return value is 0 or 1. */
        return !!test_bit(bit, buffer->scan_mask);
};

static ssize_t iio_scan_el_store(struct device *dev,
                                 struct device_attribute *attr,
                                 const char *buf,
                                 size_t len)
{
        int ret;
        bool state;
        struct iio_dev *indio_dev = dev_to_iio_dev(dev);
        struct iio_buffer *buffer = indio_dev->buffer;
        struct iio_dev_attr *this_attr = to_iio_dev_attr(attr);

        ret = strtobool(buf, &state);
        if (ret < 0)
                return ret;
        mutex_lock(&indio_dev->mlock);
        if (iio_buffer_is_active(indio_dev->buffer)) {
                ret = -EBUSY;
                goto error_ret;
        }
        ret = iio_scan_mask_query(indio_dev, buffer, this_attr->address);
        if (ret < 0)
                goto error_ret;
        if (!state && ret) {
                ret = iio_scan_mask_clear(buffer, this_attr->address);
                if (ret)
                        goto error_ret;
        } else if (state && !ret) {
                ret = iio_scan_mask_set(indio_dev, buffer, this_attr->address);
                if (ret)
                        goto error_ret;
        }

error_ret:
        mutex_unlock(&indio_dev->mlock);

        return ret < 0 ? ret : len;

}

static ssize_t iio_scan_el_ts_show(struct device *dev,
                                   struct device_attribute *attr,
                                   char *buf)
{
        struct iio_dev *indio_dev = dev_to_iio_dev(dev);
        return sprintf(buf, "%d\n", indio_dev->buffer->scan_timestamp);
}

static ssize_t iio_scan_el_ts_store(struct device *dev,
                                    struct device_attribute *attr,
                                    const char *buf,
                                    size_t len)
{
        int ret;
        struct iio_dev *indio_dev = dev_to_iio_dev(dev);
        bool state;

        ret = strtobool(buf, &state);
        if (ret < 0)
                return ret;

        mutex_lock(&indio_dev->mlock);
        if (iio_buffer_is_active(indio_dev->buffer)) {
                ret = -EBUSY;
                goto error_ret;
        }
        indio_dev->buffer->scan_timestamp = state;
error_ret:
        mutex_unlock(&indio_dev->mlock);

        return ret ? ret : len;
}

static int iio_buffer_add_channel_sysfs(struct iio_dev *indio_dev,
                                        const struct iio_chan_spec *chan)
{
        int ret, attrcount = 0;
        struct iio_buffer *buffer = indio_dev->buffer;

        ret = __iio_add_chan_devattr("index",
                                     chan,
                                     &iio_show_scan_index,
                                     NULL,
                                     0,
                                     IIO_SEPARATE,
                                     &indio_dev->dev,
                                     &buffer->scan_el_dev_attr_list);
        if (ret)
                return ret;
        attrcount++;
        ret = __iio_add_chan_devattr("type",
                                     chan,
                                     &iio_show_fixed_type,
                                     NULL,
                                     0,
                                     0,
                                     &indio_dev->dev,
                                     &buffer->scan_el_dev_attr_list);
        if (ret)
                return ret;
        attrcount++;
        if (chan->type != IIO_TIMESTAMP)
                ret = __iio_add_chan_devattr("en",
                                             chan,
                                             &iio_scan_el_show,
                                             &iio_scan_el_store,
                                             chan->scan_index,
                                             0,
                                             &indio_dev->dev,
                                             &buffer->scan_el_dev_attr_list);
        else
                ret = __iio_add_chan_devattr("en",
                                             chan,
                                             &iio_scan_el_ts_show,
                                             &iio_scan_el_ts_store,
                                             chan->scan_index,
                                             0,
                                             &indio_dev->dev,
                                             &buffer->scan_el_dev_attr_list);
        if (ret)
                return ret;
        attrcount++;
        ret = attrcount;
        return ret;
}

static ssize_t iio_buffer_read_length(struct device *dev,
                                      struct device_attribute *attr,
                                      char *buf)
{
        struct iio_dev *indio_dev = dev_to_iio_dev(dev);
        struct iio_buffer *buffer = indio_dev->buffer;

        return sprintf(buf, "%d\n", buffer->length);
}

static ssize_t iio_buffer_write_length(struct device *dev,
                                       struct device_attribute *attr,
                                       const char *buf, size_t len)
{
        struct iio_dev *indio_dev = dev_to_iio_dev(dev);
        struct iio_buffer *buffer = indio_dev->buffer;
        unsigned int val;
        int ret;

        ret = kstrtouint(buf, 10, &val);
        if (ret)
                return ret;

        if (val == buffer->length)
                return len;

        mutex_lock(&indio_dev->mlock);
        if (iio_buffer_is_active(indio_dev->buffer)) {
                ret = -EBUSY;
        } else {
                buffer->access->set_length(buffer, val);
                ret = 0;
        }
        if (ret)
                goto out;
        if (buffer->length && buffer->length < buffer->watermark)
                buffer->watermark = buffer->length;
out:
        mutex_unlock(&indio_dev->mlock);

        return ret ? ret : len;
}

static ssize_t iio_buffer_show_enable(struct device *dev,
                                      struct device_attribute *attr,
                                      char *buf)
{
        struct iio_dev *indio_dev = dev_to_iio_dev(dev);
        return sprintf(buf, "%d\n", iio_buffer_is_active(indio_dev->buffer));
}

static unsigned int iio_storage_bytes_for_si(struct iio_dev *indio_dev,
                                             unsigned int scan_index)
{
        const struct iio_chan_spec *ch;
        unsigned int bytes;

        ch = iio_find_channel_from_si(indio_dev, scan_index);
        bytes = ch->scan_type.storagebits / 8;
        if (ch->scan_type.repeat > 1)
                bytes *= ch->scan_type.repeat;
        return bytes;
}

static unsigned int iio_storage_bytes_for_timestamp(struct iio_dev *indio_dev)
{
        return iio_storage_bytes_for_si(indio_dev,
                                        indio_dev->scan_index_timestamp);
}

static int iio_compute_scan_bytes(struct iio_dev *indio_dev,
                                const unsigned long *mask, bool timestamp)
{
        unsigned bytes = 0;
        int length, i;

        /* How much space will the demuxed element take? */
        for_each_set_bit(i, mask,
                         indio_dev->masklength) {
                length = iio_storage_bytes_for_si(indio_dev, i);
                bytes = ALIGN(bytes, length);
                bytes += length;
        }

        if (timestamp) {
                length = iio_storage_bytes_for_timestamp(indio_dev);
                bytes = ALIGN(bytes, length);
                bytes += length;
        }
        return bytes;
}

static void iio_buffer_activate(struct iio_dev *indio_dev,
        struct iio_buffer *buffer)
{
        iio_buffer_get(buffer);
        list_add(&buffer->buffer_list, &indio_dev->buffer_list);
}

static void iio_buffer_deactivate(struct iio_buffer *buffer)
{
        list_del_init(&buffer->buffer_list);
        wake_up_interruptible(&buffer->pollq);
        iio_buffer_put(buffer);
}

static void iio_buffer_deactivate_all(struct iio_dev *indio_dev)
{
        struct iio_buffer *buffer, *_buffer;

        list_for_each_entry_safe(buffer, _buffer,
                        &indio_dev->buffer_list, buffer_list)
                iio_buffer_deactivate(buffer);
}

static int iio_buffer_enable(struct iio_buffer *buffer,
        struct iio_dev *indio_dev)
{
        if (!buffer->access->enable)
                return 0;
        return buffer->access->enable(buffer, indio_dev);
}

static int iio_buffer_disable(struct iio_buffer *buffer,
        struct iio_dev *indio_dev)
{
        if (!buffer->access->disable)
                return 0;
        return buffer->access->disable(buffer, indio_dev);
}

static void iio_buffer_update_bytes_per_datum(struct iio_dev *indio_dev,
        struct iio_buffer *buffer)
{
        unsigned int bytes;

        if (!buffer->access->set_bytes_per_datum)
                return;

        bytes = iio_compute_scan_bytes(indio_dev, buffer->scan_mask,
                buffer->scan_timestamp);

        buffer->access->set_bytes_per_datum(buffer, bytes);
}

static int iio_buffer_request_update(struct iio_dev *indio_dev,
        struct iio_buffer *buffer)
{
        int ret;

        iio_buffer_update_bytes_per_datum(indio_dev, buffer);
        if (buffer->access->request_update) {
                ret = buffer->access->request_update(buffer);
                if (ret) {
                        dev_dbg(&indio_dev->dev,
                               "Buffer not started: buffer parameter update failed (%d)\n",
                                ret);
                        return ret;
                }
        }

        return 0;
}

static void iio_free_scan_mask(struct iio_dev *indio_dev,
        const unsigned long *mask)
{
        /* If the mask is dynamically allocated free it, otherwise do nothing */
        if (!indio_dev->available_scan_masks)
                kfree(mask);
}

struct iio_device_config {
        unsigned int mode;
        unsigned int watermark;
        const unsigned long *scan_mask;
        unsigned int scan_bytes;
        bool scan_timestamp;
};

static int iio_verify_update(struct iio_dev *indio_dev,
        struct iio_buffer *insert_buffer, struct iio_buffer *remove_buffer,
        struct iio_device_config *config)
{
        unsigned long *compound_mask;
        const unsigned long *scan_mask;
        bool strict_scanmask = false;
        struct iio_buffer *buffer;
        bool scan_timestamp;
        unsigned int modes;

        memset(config, 0, sizeof(*config));
        config->watermark = ~0;

        /*
         * If there is just one buffer and we are removing it there is nothing
         * to verify.
         */
        if (remove_buffer && !insert_buffer &&
                list_is_singular(&indio_dev->buffer_list))
                        return 0;

        modes = indio_dev->modes;

        list_for_each_entry(buffer, &indio_dev->buffer_list, buffer_list) {
                if (buffer == remove_buffer)
                        continue;
                modes &= buffer->access->modes;
                config->watermark = min(config->watermark, buffer->watermark);
        }

        if (insert_buffer) {
                modes &= insert_buffer->access->modes;
                config->watermark = min(config->watermark,
                        insert_buffer->watermark);
        }

        /* Definitely possible for devices to support both of these. */
        if ((modes & INDIO_BUFFER_TRIGGERED) && indio_dev->trig) {
                config->mode = INDIO_BUFFER_TRIGGERED;
        } else if (modes & INDIO_BUFFER_HARDWARE) {
                /*
                 * Keep things simple for now and only allow a single buffer to
                 * be connected in hardware mode.
                 */
                if (insert_buffer && !list_empty(&indio_dev->buffer_list))
                        return -EINVAL;
                config->mode = INDIO_BUFFER_HARDWARE;
                strict_scanmask = true;
        } else if (modes & INDIO_BUFFER_SOFTWARE) {
                config->mode = INDIO_BUFFER_SOFTWARE;
        } else {
                /* Can only occur on first buffer */
                if (indio_dev->modes & INDIO_BUFFER_TRIGGERED)
                        dev_dbg(&indio_dev->dev, "Buffer not started: no trigger\n");
                return -EINVAL;
        }

        /* What scan mask do we actually have? */
        compound_mask = kcalloc(BITS_TO_LONGS(indio_dev->masklength),
                                sizeof(long), GFP_KERNEL);
        if (compound_mask == NULL)
                return -ENOMEM;

        scan_timestamp = false;

        list_for_each_entry(buffer, &indio_dev->buffer_list, buffer_list) {
                if (buffer == remove_buffer)
                        continue;
                bitmap_or(compound_mask, compound_mask, buffer->scan_mask,
                          indio_dev->masklength);
                scan_timestamp |= buffer->scan_timestamp;
        }

        if (insert_buffer) {
                bitmap_or(compound_mask, compound_mask,
                          insert_buffer->scan_mask, indio_dev->masklength);
                scan_timestamp |= insert_buffer->scan_timestamp;
        }

        if (indio_dev->available_scan_masks) {
                scan_mask = iio_scan_mask_match(indio_dev->available_scan_masks,
                                    indio_dev->masklength,
                                    compound_mask,
                                    strict_scanmask);
                kfree(compound_mask);
                if (scan_mask == NULL)
                        return -EINVAL;
        } else {
            scan_mask = compound_mask;
        }

        config->scan_bytes = iio_compute_scan_bytes(indio_dev,
                                    scan_mask, scan_timestamp);
        config->scan_mask = scan_mask;
        config->scan_timestamp = scan_timestamp;

        return 0;
}

/**
 * struct iio_demux_table - table describing demux memcpy ops
 * @from:       index to copy from
 * @to:         index to copy to
 * @length:     how many bytes to copy
 * @l:          list head used for management
 */
struct iio_demux_table {
        unsigned from;
        unsigned to;
        unsigned length;
        struct list_head l;
};

static void iio_buffer_demux_free(struct iio_buffer *buffer)
{
        struct iio_demux_table *p, *q;
        list_for_each_entry_safe(p, q, &buffer->demux_list, l) {
                list_del(&p->l);
                kfree(p);
        }
}

static int iio_buffer_add_demux(struct iio_buffer *buffer,
        struct iio_demux_table **p, unsigned int in_loc, unsigned int out_loc,
        unsigned int length)
{

        if (*p && (*p)->from + (*p)->length == in_loc &&
                (*p)->to + (*p)->length == out_loc) {
                (*p)->length += length;
        } else {
                *p = kmalloc(sizeof(**p), GFP_KERNEL);
                if (*p == NULL)
                        return -ENOMEM;
                (*p)->from = in_loc;
                (*p)->to = out_loc;
                (*p)->length = length;
                list_add_tail(&(*p)->l, &buffer->demux_list);
        }

        return 0;
}

static int iio_buffer_update_demux(struct iio_dev *indio_dev,
                                   struct iio_buffer *buffer)
{
        int ret, in_ind = -1, out_ind, length;
        unsigned in_loc = 0, out_loc = 0;
        struct iio_demux_table *p = NULL;

        /* Clear out any old demux */
        iio_buffer_demux_free(buffer);
        kfree(buffer->demux_bounce);
        buffer->demux_bounce = NULL;

        /* First work out which scan mode we will actually have */
        if (bitmap_equal(indio_dev->active_scan_mask,
                         buffer->scan_mask,
                         indio_dev->masklength))
                return 0;

        /* Now we have the two masks, work from least sig and build up sizes */
        for_each_set_bit(out_ind,
                         buffer->scan_mask,
                         indio_dev->masklength) {
                in_ind = find_next_bit(indio_dev->active_scan_mask,
                                       indio_dev->masklength,
                                       in_ind + 1);
                while (in_ind != out_ind) {
                        in_ind = find_next_bit(indio_dev->active_scan_mask,
                                               indio_dev->masklength,
                                               in_ind + 1);
                        length = iio_storage_bytes_for_si(indio_dev, in_ind);
                        /* Make sure we are aligned */
                        in_loc = roundup(in_loc, length) + length;
                }
                length = iio_storage_bytes_for_si(indio_dev, in_ind);
                out_loc = roundup(out_loc, length);
                in_loc = roundup(in_loc, length);
                ret = iio_buffer_add_demux(buffer, &p, in_loc, out_loc, length);
                if (ret)
                        goto error_clear_mux_table;
                out_loc += length;
                in_loc += length;
        }
        /* Relies on scan_timestamp being last */
        if (buffer->scan_timestamp) {
                length = iio_storage_bytes_for_timestamp(indio_dev);
                out_loc = roundup(out_loc, length);
                in_loc = roundup(in_loc, length);
                ret = iio_buffer_add_demux(buffer, &p, in_loc, out_loc, length);
                if (ret)
                        goto error_clear_mux_table;
                out_loc += length;
                in_loc += length;
        }
        buffer->demux_bounce = kzalloc(out_loc, GFP_KERNEL);
        if (buffer->demux_bounce == NULL) {
                ret = -ENOMEM;
                goto error_clear_mux_table;
        }
        return 0;

error_clear_mux_table:
        iio_buffer_demux_free(buffer);

        return ret;
}

static int iio_update_demux(struct iio_dev *indio_dev)
{
        struct iio_buffer *buffer;
        int ret;

        list_for_each_entry(buffer, &indio_dev->buffer_list, buffer_list) {
                ret = iio_buffer_update_demux(indio_dev, buffer);
                if (ret < 0)
                        goto error_clear_mux_table;
        }
        return 0;

error_clear_mux_table:
        list_for_each_entry(buffer, &indio_dev->buffer_list, buffer_list)
                iio_buffer_demux_free(buffer);

        return ret;
}

static int iio_enable_buffers(struct iio_dev *indio_dev,
        struct iio_device_config *config)
{
        struct iio_buffer *buffer;
        int ret;

        indio_dev->active_scan_mask = config->scan_mask;
        indio_dev->scan_timestamp = config->scan_timestamp;
        indio_dev->scan_bytes = config->scan_bytes;

        iio_update_demux(indio_dev);

        /* Wind up again */
        if (indio_dev->setup_ops->preenable) {
                ret = indio_dev->setup_ops->preenable(indio_dev);
                if (ret) {
                        dev_dbg(&indio_dev->dev,
                               "Buffer not started: buffer preenable failed (%d)\n", ret);
                        goto err_undo_config;
                }
        }

        if (indio_dev->info->update_scan_mode) {
                ret = indio_dev->info
                        ->update_scan_mode(indio_dev,
                                           indio_dev->active_scan_mask);
                if (ret < 0) {
                        dev_dbg(&indio_dev->dev,
                                "Buffer not started: update scan mode failed (%d)\n",
                                ret);
                        goto err_run_postdisable;
                }
        }

        if (indio_dev->info->hwfifo_set_watermark)
                indio_dev->info->hwfifo_set_watermark(indio_dev,
                        config->watermark);

        list_for_each_entry(buffer, &indio_dev->buffer_list, buffer_list) {
                ret = iio_buffer_enable(buffer, indio_dev);
                if (ret)
                        goto err_disable_buffers;
        }

        indio_dev->currentmode = config->mode;

        if (indio_dev->setup_ops->postenable) {
                ret = indio_dev->setup_ops->postenable(indio_dev);
                if (ret) {
                        dev_dbg(&indio_dev->dev,
                               "Buffer not started: postenable failed (%d)\n", ret);
                        goto err_disable_buffers;
                }
        }

        return 0;

err_disable_buffers:
        list_for_each_entry_continue_reverse(buffer, &indio_dev->buffer_list,
                                             buffer_list)
                iio_buffer_disable(buffer, indio_dev);
err_run_postdisable:
        indio_dev->currentmode = INDIO_DIRECT_MODE;
        if (indio_dev->setup_ops->postdisable)
                indio_dev->setup_ops->postdisable(indio_dev);
err_undo_config:
        indio_dev->active_scan_mask = NULL;

        return ret;
}

static int iio_disable_buffers(struct iio_dev *indio_dev)
{
        struct iio_buffer *buffer;
        int ret = 0;
        int ret2;

        /* Wind down existing buffers - iff there are any */
        if (list_empty(&indio_dev->buffer_list))
                return 0;

        /*
         * If things go wrong at some step in disable we still need to continue
         * to perform the other steps, otherwise we leave the device in a
         * inconsistent state. We return the error code for the first error we
         * encountered.
         */

        if (indio_dev->setup_ops->predisable) {
                ret2 = indio_dev->setup_ops->predisable(indio_dev);
                if (ret2 && !ret)
                        ret = ret2;

        }

        list_for_each_entry(buffer, &indio_dev->buffer_list, buffer_list) {
                ret2 = iio_buffer_disable(buffer, indio_dev);
                if (ret2 && !ret)
                        ret = ret2;
        }

        indio_dev->currentmode = INDIO_DIRECT_MODE;

        if (indio_dev->setup_ops->postdisable) {
                ret2 = indio_dev->setup_ops->postdisable(indio_dev);
                if (ret2 && !ret)
                        ret = ret2;
        }

        iio_free_scan_mask(indio_dev, indio_dev->active_scan_mask);
        indio_dev->active_scan_mask = NULL;

        return ret;
}

static int __iio_update_buffers(struct iio_dev *indio_dev,
                       struct iio_buffer *insert_buffer,
                       struct iio_buffer *remove_buffer)
{
        struct iio_device_config new_config;
        int ret;

        ret = iio_verify_update(indio_dev, insert_buffer, remove_buffer,
                &new_config);
        if (ret)
                return ret;

        if (insert_buffer) {
                ret = iio_buffer_request_update(indio_dev, insert_buffer);
                if (ret)
                        goto err_free_config;
        }

        ret = iio_disable_buffers(indio_dev);
        if (ret)
                goto err_deactivate_all;

        if (remove_buffer)
                iio_buffer_deactivate(remove_buffer);
        if (insert_buffer)
                iio_buffer_activate(indio_dev, insert_buffer);

        /* If no buffers in list, we are done */
        if (list_empty(&indio_dev->buffer_list))
                return 0;

        ret = iio_enable_buffers(indio_dev, &new_config);
        if (ret)
                goto err_deactivate_all;

        return 0;

err_deactivate_all:
        /*
         * We've already verified that the config is valid earlier. If things go
         * wrong in either enable or disable the most likely reason is an IO
         * error from the device. In this case there is no good recovery
         * strategy. Just make sure to disable everything and leave the device
         * in a sane state.  With a bit of luck the device might come back to
         * life again later and userspace can try again.
         */
        iio_buffer_deactivate_all(indio_dev);

err_free_config:
        iio_free_scan_mask(indio_dev, new_config.scan_mask);
        return ret;
}

int iio_update_buffers(struct iio_dev *indio_dev,
                       struct iio_buffer *insert_buffer,
                       struct iio_buffer *remove_buffer)
{
        int ret;

        if (insert_buffer == remove_buffer)
                return 0;

        mutex_lock(&indio_dev->info_exist_lock);
        mutex_lock(&indio_dev->mlock);

        if (insert_buffer && iio_buffer_is_active(insert_buffer))
                insert_buffer = NULL;

        if (remove_buffer && !iio_buffer_is_active(remove_buffer))
                remove_buffer = NULL;

        if (!insert_buffer && !remove_buffer) {
                ret = 0;
                goto out_unlock;
        }

        if (indio_dev->info == NULL) {
                ret = -ENODEV;
                goto out_unlock;
        }

        ret = __iio_update_buffers(indio_dev, insert_buffer, remove_buffer);

out_unlock:
        mutex_unlock(&indio_dev->mlock);
        mutex_unlock(&indio_dev->info_exist_lock);

        return ret;
}
EXPORT_SYMBOL_GPL(iio_update_buffers);

void iio_disable_all_buffers(struct iio_dev *indio_dev)
{
        iio_disable_buffers(indio_dev);
        iio_buffer_deactivate_all(indio_dev);
}

static ssize_t iio_buffer_store_enable(struct device *dev,
                                       struct device_attribute *attr,
                                       const char *buf,
                                       size_t len)
{
        int ret;
        bool requested_state;
        struct iio_dev *indio_dev = dev_to_iio_dev(dev);
        bool inlist;

        ret = strtobool(buf, &requested_state);
        if (ret < 0)
                return ret;

        mutex_lock(&indio_dev->mlock);

        /* Find out if it is in the list */
        inlist = iio_buffer_is_active(indio_dev->buffer);
        /* Already in desired state */
        if (inlist == requested_state)
                goto done;

        if (requested_state)
                ret = __iio_update_buffers(indio_dev,
                                         indio_dev->buffer, NULL);
        else
                ret = __iio_update_buffers(indio_dev,
                                         NULL, indio_dev->buffer);

done:
        mutex_unlock(&indio_dev->mlock);
        return (ret < 0) ? ret : len;
}

static const char * const iio_scan_elements_group_name = "scan_elements";

static ssize_t iio_buffer_show_watermark(struct device *dev,
                                         struct device_attribute *attr,
                                         char *buf)
{
        struct iio_dev *indio_dev = dev_to_iio_dev(dev);
        struct iio_buffer *buffer = indio_dev->buffer;

        return sprintf(buf, "%u\n", buffer->watermark);
}

static ssize_t iio_buffer_store_watermark(struct device *dev,
                                          struct device_attribute *attr,
                                          const char *buf,
                                          size_t len)
{
        struct iio_dev *indio_dev = dev_to_iio_dev(dev);
        struct iio_buffer *buffer = indio_dev->buffer;
        unsigned int val;
        int ret;

        ret = kstrtouint(buf, 10, &val);
        if (ret)
                return ret;
        if (!val)
                return -EINVAL;

        mutex_lock(&indio_dev->mlock);

        if (val > buffer->length) {
                ret = -EINVAL;
                goto out;
        }

        if (iio_buffer_is_active(indio_dev->buffer)) {
                ret = -EBUSY;
                goto out;
        }

        buffer->watermark = val;
out:
        mutex_unlock(&indio_dev->mlock);

        return ret ? ret : len;
}

static DEVICE_ATTR(length, S_IRUGO | S_IWUSR, iio_buffer_read_length,
                   iio_buffer_write_length);
static struct device_attribute dev_attr_length_ro = __ATTR(length,
        S_IRUGO, iio_buffer_read_length, NULL);
static DEVICE_ATTR(enable, S_IRUGO | S_IWUSR,
                   iio_buffer_show_enable, iio_buffer_store_enable);
static DEVICE_ATTR(watermark, S_IRUGO | S_IWUSR,
                   iio_buffer_show_watermark, iio_buffer_store_watermark);
static struct device_attribute dev_attr_watermark_ro = __ATTR(watermark,
        S_IRUGO, iio_buffer_show_watermark, NULL);

static struct attribute *iio_buffer_attrs[] = {
        &dev_attr_length.attr,
        &dev_attr_enable.attr,
        &dev_attr_watermark.attr,
};

int iio_buffer_alloc_sysfs_and_mask(struct iio_dev *indio_dev)
{
        struct iio_dev_attr *p;
        struct attribute **attr;
        struct iio_buffer *buffer = indio_dev->buffer;
        int ret, i, attrn, attrcount, attrcount_orig = 0;
        const struct iio_chan_spec *channels;

        channels = indio_dev->channels;
        if (channels) {
                int ml = indio_dev->masklength;

                for (i = 0; i < indio_dev->num_channels; i++)
                        ml = max(ml, channels[i].scan_index + 1);
                indio_dev->masklength = ml;
        }

        if (!buffer)
                return 0;

        attrcount = 0;
        if (buffer->attrs) {
                while (buffer->attrs[attrcount] != NULL)
                        attrcount++;
        }

        attr = kcalloc(attrcount + ARRAY_SIZE(iio_buffer_attrs) + 1,
                       sizeof(struct attribute *), GFP_KERNEL);
        if (!attr)
                return -ENOMEM;

        memcpy(attr, iio_buffer_attrs, sizeof(iio_buffer_attrs));
        if (!buffer->access->set_length)
                attr[0] = &dev_attr_length_ro.attr;

        if (buffer->access->flags & INDIO_BUFFER_FLAG_FIXED_WATERMARK)
                attr[2] = &dev_attr_watermark_ro.attr;

        if (buffer->attrs)
                memcpy(&attr[ARRAY_SIZE(iio_buffer_attrs)], buffer->attrs,
                       sizeof(struct attribute *) * attrcount);

        attr[attrcount + ARRAY_SIZE(iio_buffer_attrs)] = NULL;

        buffer->buffer_group.name = "buffer";
        buffer->buffer_group.attrs = attr;

        indio_dev->groups[indio_dev->groupcounter++] = &buffer->buffer_group;

        if (buffer->scan_el_attrs != NULL) {
                attr = buffer->scan_el_attrs->attrs;
                while (*attr++ != NULL)
                        attrcount_orig++;
        }
        attrcount = attrcount_orig;
        INIT_LIST_HEAD(&buffer->scan_el_dev_attr_list);
        channels = indio_dev->channels;
        if (channels) {
                /* new magic */
                for (i = 0; i < indio_dev->num_channels; i++) {
                        if (channels[i].scan_index < 0)
                                continue;

                        ret = iio_buffer_add_channel_sysfs(indio_dev,
                                                         &channels[i]);
                        if (ret < 0)
                                goto error_cleanup_dynamic;
                        attrcount += ret;
                        if (channels[i].type == IIO_TIMESTAMP)
                                indio_dev->scan_index_timestamp =
                                        channels[i].scan_index;
                }
                if (indio_dev->masklength && buffer->scan_mask == NULL) {
                        buffer->scan_mask = kcalloc(BITS_TO_LONGS(indio_dev->masklength),
                                                    sizeof(*buffer->scan_mask),
                                                    GFP_KERNEL);
                        if (buffer->scan_mask == NULL) {
                                ret = -ENOMEM;
                                goto error_cleanup_dynamic;
                        }
                }
        }

        buffer->scan_el_group.name = iio_scan_elements_group_name;

        buffer->scan_el_group.attrs = kcalloc(attrcount + 1,
                                              sizeof(buffer->scan_el_group.attrs[0]),
                                              GFP_KERNEL);
        if (buffer->scan_el_group.attrs == NULL) {
                ret = -ENOMEM;
                goto error_free_scan_mask;
        }
        if (buffer->scan_el_attrs)
                memcpy(buffer->scan_el_group.attrs, buffer->scan_el_attrs,
                       sizeof(buffer->scan_el_group.attrs[0])*attrcount_orig);
        attrn = attrcount_orig;

        list_for_each_entry(p, &buffer->scan_el_dev_attr_list, l)
                buffer->scan_el_group.attrs[attrn++] = &p->dev_attr.attr;
        indio_dev->groups[indio_dev->groupcounter++] = &buffer->scan_el_group;

        return 0;

error_free_scan_mask:
        kfree(buffer->scan_mask);
error_cleanup_dynamic:
        iio_free_chan_devattr_list(&buffer->scan_el_dev_attr_list);
        kfree(indio_dev->buffer->buffer_group.attrs);

        return ret;
}

void iio_buffer_free_sysfs_and_mask(struct iio_dev *indio_dev)
{
        if (!indio_dev->buffer)
                return;

        kfree(indio_dev->buffer->scan_mask);
        kfree(indio_dev->buffer->buffer_group.attrs);
        kfree(indio_dev->buffer->scan_el_group.attrs);
        iio_free_chan_devattr_list(&indio_dev->buffer->scan_el_dev_attr_list);
}

/**
 * iio_validate_scan_mask_onehot() - Validates that exactly one channel is selected
 * @indio_dev: the iio device
 * @mask: scan mask to be checked
 *
 * Return true if exactly one bit is set in the scan mask, false otherwise. It
 * can be used for devices where only one channel can be active for sampling at
 * a time.
 */
bool iio_validate_scan_mask_onehot(struct iio_dev *indio_dev,
        const unsigned long *mask)
{
        return bitmap_weight(mask, indio_dev->masklength) == 1;
}
EXPORT_SYMBOL_GPL(iio_validate_scan_mask_onehot);

static const void *iio_demux(struct iio_buffer *buffer,
                                 const void *datain)
{
        struct iio_demux_table *t;

        if (list_empty(&buffer->demux_list))
                return datain;
        list_for_each_entry(t, &buffer->demux_list, l)
                memcpy(buffer->demux_bounce + t->to,
                       datain + t->from, t->length);

        return buffer->demux_bounce;
}

static int iio_push_to_buffer(struct iio_buffer *buffer, const void *data)
{
        const void *dataout = iio_demux(buffer, data);
        int ret;

        ret = buffer->access->store_to(buffer, dataout);
        if (ret)
                return ret;

        /*
         * We can't just test for watermark to decide if we wake the poll queue
         * because read may request less samples than the watermark.
         */
        wake_up_interruptible_poll(&buffer->pollq, POLLIN | POLLRDNORM);
        return 0;
}

/**
 * iio_push_to_buffers() - push to a registered buffer.
 * @indio_dev:          iio_dev structure for device.
 * @data:               Full scan.
 */
int iio_push_to_buffers(struct iio_dev *indio_dev, const void *data)
{
        int ret;
        struct iio_buffer *buf;

        list_for_each_entry(buf, &indio_dev->buffer_list, buffer_list) {
                ret = iio_push_to_buffer(buf, data);
                if (ret < 0)
                        return ret;
        }

        return 0;
}
EXPORT_SYMBOL_GPL(iio_push_to_buffers);

/**
 * iio_buffer_release() - Free a buffer's resources
 * @ref: Pointer to the kref embedded in the iio_buffer struct
 *
 * This function is called when the last reference to the buffer has been
 * dropped. It will typically free all resources allocated by the buffer. Do not
 * call this function manually, always use iio_buffer_put() when done using a
 * buffer.
 */
static void iio_buffer_release(struct kref *ref)
{
        struct iio_buffer *buffer = container_of(ref, struct iio_buffer, ref);

        buffer->access->release(buffer);
}

/**
 * iio_buffer_get() - Grab a reference to the buffer
 * @buffer: The buffer to grab a reference for, may be NULL
 *
 * Returns the pointer to the buffer that was passed into the function.
 */
struct iio_buffer *iio_buffer_get(struct iio_buffer *buffer)
{
        if (buffer)
                kref_get(&buffer->ref);

        return buffer;
}
EXPORT_SYMBOL_GPL(iio_buffer_get);

/**
 * iio_buffer_put() - Release the reference to the buffer
 * @buffer: The buffer to release the reference for, may be NULL
 */
void iio_buffer_put(struct iio_buffer *buffer)
{
        if (buffer)
                kref_put(&buffer->ref, iio_buffer_release);
}
EXPORT_SYMBOL_GPL(iio_buffer_put);

/**
 * iio_device_attach_buffer - Attach a buffer to a IIO device
 * @indio_dev: The device the buffer should be attached to
 * @buffer: The buffer to attach to the device
 *
 * This function attaches a buffer to a IIO device. The buffer stays attached to
 * the device until the device is freed. The function should only be called at
 * most once per device.
 */
void iio_device_attach_buffer(struct iio_dev *indio_dev,
                              struct iio_buffer *buffer)
{
        indio_dev->buffer = iio_buffer_get(buffer);
}
EXPORT_SYMBOL_GPL(iio_device_attach_buffer);