/* The industrial I/O simple minimally locked ring buffer.
 *
 * 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.
 */

#include <linux/slab.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/device.h>
#include <linux/workqueue.h>
#include <linux/sched.h>
#include <linux/poll.h>
#include "ring_sw.h"
#include "trigger.h"

/**
 * struct iio_sw_ring_buffer - software ring buffer
 * @buf:                generic ring buffer elements
 * @data:               the ring buffer memory
 * @read_p:             read pointer (oldest available)
 * @write_p:            write pointer
 * @last_written_p:     read pointer (newest available)
 * @half_p:             half buffer length behind write_p (event generation)
 * @use_count:          reference count to prevent resizing when in use
 * @update_needed:      flag to indicated change in size requested
 * @use_lock:           lock to prevent change in size when in use
 *
 * Note that the first element of all ring buffers must be a
 * struct iio_buffer.
**/
struct iio_sw_ring_buffer {
        struct iio_buffer  buf;
        unsigned char           *data;
        unsigned char           *read_p;
        unsigned char           *write_p;
        unsigned char           *last_written_p;
        /* used to act as a point at which to signal an event */
        unsigned char           *half_p;
        int                     use_count;
        int                     update_needed;
        spinlock_t              use_lock;
};

#define iio_to_sw_ring(r) container_of(r, struct iio_sw_ring_buffer, buf)

static inline int __iio_allocate_sw_ring_buffer(struct iio_sw_ring_buffer *ring,
                                                int bytes_per_datum, int length)
{
        if ((length == 0) || (bytes_per_datum == 0))
                return -EINVAL;
        __iio_update_buffer(&ring->buf, bytes_per_datum, length);
        ring->data = kmalloc(length*ring->buf.bytes_per_datum, GFP_ATOMIC);
        ring->read_p = NULL;
        ring->write_p = NULL;
        ring->last_written_p = NULL;
        ring->half_p = NULL;
        return ring->data ? 0 : -ENOMEM;
}

static inline void __iio_init_sw_ring_buffer(struct iio_sw_ring_buffer *ring)
{
        spin_lock_init(&ring->use_lock);
}

static inline void __iio_free_sw_ring_buffer(struct iio_sw_ring_buffer *ring)
{
        kfree(ring->data);
}

static void iio_mark_sw_rb_in_use(struct iio_buffer *r)
{
        struct iio_sw_ring_buffer *ring = iio_to_sw_ring(r);
        spin_lock(&ring->use_lock);
        ring->use_count++;
        spin_unlock(&ring->use_lock);
}

static void iio_unmark_sw_rb_in_use(struct iio_buffer *r)
{
        struct iio_sw_ring_buffer *ring = iio_to_sw_ring(r);
        spin_lock(&ring->use_lock);
        ring->use_count--;
        spin_unlock(&ring->use_lock);
}


/* Ring buffer related functionality */
/* Store to ring is typically called in the bh of a data ready interrupt handler
 * in the device driver */
/* Lock always held if their is a chance this may be called */
/* Only one of these per ring may run concurrently - enforced by drivers */
static int iio_store_to_sw_ring(struct iio_sw_ring_buffer *ring,
                                unsigned char *data, s64 timestamp)
{
        int ret = 0;
        unsigned char *temp_ptr, *change_test_ptr;

        /* initial store */
        if (unlikely(ring->write_p == NULL)) {
                ring->write_p = ring->data;
                /* Doesn't actually matter if this is out of the set
                 * as long as the read pointer is valid before this
                 * passes it - guaranteed as set later in this function.
                 */
                ring->half_p = ring->data - ring->buf.length*ring->buf.bytes_per_datum/2;
        }
        /* Copy data to where ever the current write pointer says */
        memcpy(ring->write_p, data, ring->buf.bytes_per_datum);
        barrier();
        /* Update the pointer used to get most recent value.
         * Always valid as either points to latest or second latest value.
         * Before this runs it is null and read attempts fail with -EAGAIN.
         */
        ring->last_written_p = ring->write_p;
        barrier();
        /* temp_ptr used to ensure we never have an invalid pointer
         * it may be slightly lagging, but never invalid
         */
        temp_ptr = ring->write_p + ring->buf.bytes_per_datum;
        /* End of ring, back to the beginning */
        if (temp_ptr == ring->data + ring->buf.length*ring->buf.bytes_per_datum)
                temp_ptr = ring->data;
        /* Update the write pointer
         * always valid as long as this is the only function able to write.
         * Care needed with smp systems to ensure more than one ring fill
         * is never scheduled.
         */
        ring->write_p = temp_ptr;

        if (ring->read_p == NULL)
                ring->read_p = ring->data;
        /* Buffer full - move the read pointer and create / escalate
         * ring event */
        /* Tricky case - if the read pointer moves before we adjust it.
         * Handle by not pushing if it has moved - may result in occasional
         * unnecessary buffer full events when it wasn't quite true.
         */
        else if (ring->write_p == ring->read_p) {
                change_test_ptr = ring->read_p;
                temp_ptr = change_test_ptr + ring->buf.bytes_per_datum;
                if (temp_ptr
                    == ring->data + ring->buf.length*ring->buf.bytes_per_datum) {
                        temp_ptr = ring->data;
                }
                /* We are moving pointer on one because the ring is full.  Any
                 * change to the read pointer will be this or greater.
                 */
                if (change_test_ptr == ring->read_p)
                        ring->read_p = temp_ptr;
        }
        /* investigate if our event barrier has been passed */
        /* There are definite 'issues' with this and chances of
         * simultaneous read */
        /* Also need to use loop count to ensure this only happens once */
        ring->half_p += ring->buf.bytes_per_datum;
        if (ring->half_p == ring->data + ring->buf.length*ring->buf.bytes_per_datum)
                ring->half_p = ring->data;
        if (ring->half_p == ring->read_p) {
                ring->buf.stufftoread = true;
                wake_up_interruptible(&ring->buf.pollq);
        }
        return ret;
}

static int iio_read_first_n_sw_rb(struct iio_buffer *r,
                                  size_t n, char __user *buf)
{
        struct iio_sw_ring_buffer *ring = iio_to_sw_ring(r);

        u8 *initial_read_p, *initial_write_p, *current_read_p, *end_read_p;
        u8 *data;
        int ret, max_copied, bytes_to_rip, dead_offset;

        /* A userspace program has probably made an error if it tries to
         *  read something that is not a whole number of bpds.
         * Return an error.
         */
        if (n % ring->buf.bytes_per_datum) {
                ret = -EINVAL;
                printk(KERN_INFO "Ring buffer read request not whole number of"
                       "samples: Request bytes %zd, Current bytes per datum %d\n",
                       n, ring->buf.bytes_per_datum);
                goto error_ret;
        }
        /* Limit size to whole of ring buffer */
        bytes_to_rip = min((size_t)(ring->buf.bytes_per_datum*ring->buf.length),
                           n);

        data = kmalloc(bytes_to_rip, GFP_KERNEL);
        if (data == NULL) {
                ret = -ENOMEM;
                goto error_ret;
        }

        /* build local copy */
        initial_read_p = ring->read_p;
        if (unlikely(initial_read_p == NULL)) { /* No data here as yet */
                ret = 0;
                goto error_free_data_cpy;
        }

        initial_write_p = ring->write_p;

        /* Need a consistent pair */
        while ((initial_read_p != ring->read_p)
               || (initial_write_p != ring->write_p)) {
                initial_read_p = ring->read_p;
                initial_write_p = ring->write_p;
        }
        if (initial_write_p == initial_read_p) {
                /* No new data available.*/
                ret = 0;
                goto error_free_data_cpy;
        }

        if (initial_write_p >= initial_read_p + bytes_to_rip) {
                /* write_p is greater than necessary, all is easy */
                max_copied = bytes_to_rip;
                memcpy(data, initial_read_p, max_copied);
                end_read_p = initial_read_p + max_copied;
        } else if (initial_write_p > initial_read_p) {
                /*not enough data to cpy */
                max_copied = initial_write_p - initial_read_p;
                memcpy(data, initial_read_p, max_copied);
                end_read_p = initial_write_p;
        } else {
                /* going through 'end' of ring buffer */
                max_copied = ring->data
                        + ring->buf.length*ring->buf.bytes_per_datum - initial_read_p;
                memcpy(data, initial_read_p, max_copied);
                /* possible we are done if we align precisely with end */
                if (max_copied == bytes_to_rip)
                        end_read_p = ring->data;
                else if (initial_write_p
                         > ring->data + bytes_to_rip - max_copied) {
                        /* enough data to finish */
                        memcpy(data + max_copied, ring->data,
                               bytes_to_rip - max_copied);
                        max_copied = bytes_to_rip;
                        end_read_p = ring->data + (bytes_to_rip - max_copied);
                } else {  /* not enough data */
                        memcpy(data + max_copied, ring->data,
                               initial_write_p - ring->data);
                        max_copied += initial_write_p - ring->data;
                        end_read_p = initial_write_p;
                }
        }
        /* Now to verify which section was cleanly copied - i.e. how far
         * read pointer has been pushed */
        current_read_p = ring->read_p;

        if (initial_read_p <= current_read_p)
                dead_offset = current_read_p - initial_read_p;
        else
                dead_offset = ring->buf.length*ring->buf.bytes_per_datum
                        - (initial_read_p - current_read_p);

        /* possible issue if the initial write has been lapped or indeed
         * the point we were reading to has been passed */
        /* No valid data read.
         * In this case the read pointer is already correct having been
         * pushed further than we would look. */
        if (max_copied - dead_offset < 0) {
                ret = 0;
                goto error_free_data_cpy;
        }

        /* setup the next read position */
        /* Beware, this may fail due to concurrency fun and games.
         *  Possible that sufficient fill commands have run to push the read
         * pointer past where we would be after the rip. If this occurs, leave
         * it be.
         */
        /* Tricky - deal with loops */

        while (ring->read_p != end_read_p)
                ring->read_p = end_read_p;

        ret = max_copied - dead_offset;

        if (copy_to_user(buf, data + dead_offset, ret))  {
                ret =  -EFAULT;
                goto error_free_data_cpy;
        }

        if (bytes_to_rip >= ring->buf.length*ring->buf.bytes_per_datum/2)
                ring->buf.stufftoread = 0;

error_free_data_cpy:
        kfree(data);
error_ret:

        return ret;
}

static int iio_store_to_sw_rb(struct iio_buffer *r,
                              u8 *data,
                              s64 timestamp)
{
        struct iio_sw_ring_buffer *ring = iio_to_sw_ring(r);
        return iio_store_to_sw_ring(ring, data, timestamp);
}

static int iio_read_last_from_sw_ring(struct iio_sw_ring_buffer *ring,
                                      unsigned char *data)
{
        unsigned char *last_written_p_copy;

        iio_mark_sw_rb_in_use(&ring->buf);
again:
        barrier();
        last_written_p_copy = ring->last_written_p;
        barrier(); /*unnessecary? */
        /* Check there is anything here */
        if (last_written_p_copy == NULL)
                return -EAGAIN;
        memcpy(data, last_written_p_copy, ring->buf.bytes_per_datum);

        if (unlikely(ring->last_written_p != last_written_p_copy))
                goto again;

        iio_unmark_sw_rb_in_use(&ring->buf);
        return 0;
}

static int iio_read_last_from_sw_rb(struct iio_buffer *r,
                             unsigned char *data)
{
        return iio_read_last_from_sw_ring(iio_to_sw_ring(r), data);
}

static int iio_request_update_sw_rb(struct iio_buffer *r)
{
        int ret = 0;
        struct iio_sw_ring_buffer *ring = iio_to_sw_ring(r);

        r->stufftoread = false;
        spin_lock(&ring->use_lock);
        if (!ring->update_needed)
                goto error_ret;
        if (ring->use_count) {
                ret = -EAGAIN;
                goto error_ret;
        }
        __iio_free_sw_ring_buffer(ring);
        ret = __iio_allocate_sw_ring_buffer(ring, ring->buf.bytes_per_datum,
                                            ring->buf.length);
error_ret:
        spin_unlock(&ring->use_lock);
        return ret;
}

static int iio_get_bytes_per_datum_sw_rb(struct iio_buffer *r)
{
        struct iio_sw_ring_buffer *ring = iio_to_sw_ring(r);
        return ring->buf.bytes_per_datum;
}

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

static int iio_get_length_sw_rb(struct iio_buffer *r)
{
        return r->length;
}

static int iio_set_length_sw_rb(struct iio_buffer *r, int length)
{
        if (r->length != length) {
                r->length = length;
                if (r->access->mark_param_change)
                        r->access->mark_param_change(r);
        }
        return 0;
}

static int iio_mark_update_needed_sw_rb(struct iio_buffer *r)
{
        struct iio_sw_ring_buffer *ring = iio_to_sw_ring(r);
        ring->update_needed = true;
        return 0;
}

static IIO_BUFFER_ENABLE_ATTR;
static IIO_BUFFER_BYTES_PER_DATUM_ATTR;
static IIO_BUFFER_LENGTH_ATTR;

/* Standard set of ring buffer attributes */
static struct attribute *iio_ring_attributes[] = {
        &dev_attr_length.attr,
        &dev_attr_bytes_per_datum.attr,
        &dev_attr_enable.attr,
        NULL,
};

static struct attribute_group iio_ring_attribute_group = {
        .attrs = iio_ring_attributes,
        .name = "buffer",
};

struct iio_buffer *iio_sw_rb_allocate(struct iio_dev *indio_dev)
{
        struct iio_buffer *buf;
        struct iio_sw_ring_buffer *ring;

        ring = kzalloc(sizeof *ring, GFP_KERNEL);
        if (!ring)
                return NULL;
        ring->update_needed = true;
        buf = &ring->buf;
        iio_buffer_init(buf, indio_dev);
        __iio_init_sw_ring_buffer(ring);
        buf->attrs = &iio_ring_attribute_group;

        return buf;
}
EXPORT_SYMBOL(iio_sw_rb_allocate);

void iio_sw_rb_free(struct iio_buffer *r)
{
        kfree(iio_to_sw_ring(r));
}
EXPORT_SYMBOL(iio_sw_rb_free);

const struct iio_buffer_access_funcs ring_sw_access_funcs = {
        .mark_in_use = &iio_mark_sw_rb_in_use,
        .unmark_in_use = &iio_unmark_sw_rb_in_use,
        .store_to = &iio_store_to_sw_rb,
        .read_last = &iio_read_last_from_sw_rb,
        .read_first_n = &iio_read_first_n_sw_rb,
        .mark_param_change = &iio_mark_update_needed_sw_rb,
        .request_update = &iio_request_update_sw_rb,
        .get_bytes_per_datum = &iio_get_bytes_per_datum_sw_rb,
        .set_bytes_per_datum = &iio_set_bytes_per_datum_sw_rb,
        .get_length = &iio_get_length_sw_rb,
        .set_length = &iio_set_length_sw_rb,
};
EXPORT_SYMBOL(ring_sw_access_funcs);

MODULE_DESCRIPTION("Industrialio I/O software ring buffer");
MODULE_LICENSE("GPL");