On Tue, Nov 06, 2007 at 02:33:53AM -0800, akpm@linux-foundation.org wrote:

[mmotm.git] / drivers / staging / iio / ring_sw.c

/* 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/kernel.h>
#include <linux/device.h>
#include <linux/module.h>
#include <linux/device.h>
#include <linux/workqueue.h>
#include "ring_sw.h"

static inline int __iio_init_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_init_ring_buffer(&ring->buf, bytes_per_datum, length);
        ring->use_lock = __SPIN_LOCK_UNLOCKED((ring)->use_lock);
        ring->data = kmalloc(length*ring->buf.bpd, GFP_KERNEL);
        ring->read_p = 0;
        ring->write_p = 0;
        ring->last_written_p = 0;
        ring->half_p = 0;
        return ring->data ? 0 : -ENOMEM;
}

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

void iio_mark_sw_rb_in_use(struct iio_ring_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);
}
EXPORT_SYMBOL(iio_mark_sw_rb_in_use);

void iio_unmark_sw_rb_in_use(struct iio_ring_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);
}
EXPORT_SYMBOL(iio_unmark_sw_rb_in_use);


/* 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 */
int iio_store_to_sw_ring(struct iio_sw_ring_buffer *ring,
                         unsigned char *data,
                         s64 timestamp)
{
        int ret = 0;
        int code;
        unsigned char *temp_ptr, *change_test_ptr;

        /* initial store */
        if (unlikely(ring->write_p == 0)) {
                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.bpd/2;
        }
        /* Copy data to where ever the current write pointer says */
        memcpy(ring->write_p, data, ring->buf.bpd);
        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.bpd;
        /* End of ring, back to the beginning */
        if (temp_ptr == ring->data + ring->buf.length*ring->buf.bpd)
                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 == 0)
                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.bpd;
                if (temp_ptr
                    == ring->data + ring->buf.length*ring->buf.bpd) {
                        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;

                spin_lock(&ring->buf.shared_ev_pointer.lock);

                ret = iio_push_or_escallate_ring_event(&ring->buf,
                                                       IIO_EVENT_CODE_RING_100_FULL,
                                                       timestamp);
                spin_unlock(&ring->buf.shared_ev_pointer.lock);
                if (ret)
                        goto error_ret;
        }
        /* 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.bpd;
        if (ring->half_p == ring->data + ring->buf.length*ring->buf.bpd)
                ring->half_p = ring->data;
        if (ring->half_p == ring->read_p) {
                spin_lock(&ring->buf.shared_ev_pointer.lock);
                code = IIO_EVENT_CODE_RING_50_FULL;
                ret = __iio_push_event(&ring->buf.ev_int,
                                       code,
                                       timestamp,
                                       &ring->buf.shared_ev_pointer);
                spin_unlock(&ring->buf.shared_ev_pointer.lock);
        }
error_ret:
        return ret;
}

int iio_rip_sw_rb(struct iio_ring_buffer *r,
                  size_t count, u8 **data, int *dead_offset)
{
        struct iio_sw_ring_buffer *ring = iio_to_sw_ring(r);

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

        /* 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 (count % ring->buf.bpd) {
                ret = -EINVAL;
                printk(KERN_INFO "Ring buffer read request not whole number of"
                       "samples: Request bytes %zd, Current bpd %d\n",
                       count, ring->buf.bpd);
                goto error_ret;
        }
        /* Limit size to whole of ring buffer */
        bytes_to_rip = min((size_t)(ring->buf.bpd*ring->buf.length), count);

        *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 == 0)) { /* 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.bpd - 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.bpd
                        - (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;

        return max_copied - *dead_offset;

error_free_data_cpy:
        kfree(*data);
error_ret:
        return ret;
}
EXPORT_SYMBOL(iio_rip_sw_rb);

int iio_store_to_sw_rb(struct iio_ring_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);
}
EXPORT_SYMBOL(iio_store_to_sw_rb);

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 == 0)
                return -EAGAIN;
        memcpy(data, last_written_p_copy, ring->buf.bpd);

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

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

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

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

        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_init_sw_ring_buffer(ring, ring->buf.bpd, ring->buf.length);
error_ret:
        spin_unlock(&ring->use_lock);
        return ret;
}
EXPORT_SYMBOL(iio_request_update_sw_rb);

int iio_get_bpd_sw_rb(struct iio_ring_buffer *r)
{
        struct iio_sw_ring_buffer *ring = iio_to_sw_ring(r);
        return ring->buf.bpd;
}
EXPORT_SYMBOL(iio_get_bpd_sw_rb);

int iio_set_bpd_sw_rb(struct iio_ring_buffer *r, size_t bpd)
{
        if (r->bpd != bpd) {
                r->bpd = bpd;
                if (r->access.mark_param_change)
                        r->access.mark_param_change(r);
        }
        return 0;
}
EXPORT_SYMBOL(iio_set_bpd_sw_rb);

int iio_get_length_sw_rb(struct iio_ring_buffer *r)
{
        return r->length;
}
EXPORT_SYMBOL(iio_get_length_sw_rb);

int iio_set_length_sw_rb(struct iio_ring_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;
}
EXPORT_SYMBOL(iio_set_length_sw_rb);

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

static void iio_sw_rb_release(struct device *dev)
{
        struct iio_ring_buffer *r = to_iio_ring_buffer(dev);
        kfree(iio_to_sw_ring(r));
}

static IIO_RING_ENABLE_ATTR;
static IIO_RING_BPS_ATTR;
static IIO_RING_LENGTH_ATTR;

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

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

static const struct attribute_group *iio_ring_attribute_groups[] = {
        &iio_ring_attribute_group,
        NULL
};

static struct device_type iio_sw_ring_type = {
        .release = iio_sw_rb_release,
        .groups = iio_ring_attribute_groups,
};

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

        ring = kzalloc(sizeof *ring, GFP_KERNEL);
        if (!ring)
                return 0;
        buf = &ring->buf;

        iio_ring_buffer_init(buf, indio_dev);
        buf->dev.type = &iio_sw_ring_type;
        device_initialize(&buf->dev);
        buf->dev.parent = &indio_dev->dev;
        buf->dev.class = &iio_class;
        dev_set_drvdata(&buf->dev, (void *)buf);

        return buf;
}
EXPORT_SYMBOL(iio_sw_rb_allocate);

void iio_sw_rb_free(struct iio_ring_buffer *r)
{
        if (r)
                iio_put_ring_buffer(r);
}
EXPORT_SYMBOL(iio_sw_rb_free);
MODULE_DESCRIPTION("Industrialio I/O software ring buffer");
MODULE_LICENSE("GPL");