/*
 * DMA-able FIFO implementation
 *
 * Copyright (C) 2012 Peter Hurley <peter@hurleysoftware.com>
 *
 * 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; either version 2 of the License, or
 * (at your option) any later version.
 *
 * 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.
 */

#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/list.h>
#include <linux/bug.h>

#include "dma_fifo.h"

#ifdef DEBUG_TRACING
#define df_trace(s, args...) pr_debug(s, ##args)
#else
#define df_trace(s, args...)
#endif

#define FAIL(fifo, condition, format...) ({                             \
        fifo->corrupt = !!(condition);                                  \
        WARN(fifo->corrupt, format);                                    \
})

/*
 * private helper fn to determine if check is in open interval (lo,hi)
 */
static bool addr_check(unsigned check, unsigned lo, unsigned hi)
{
        return check - (lo + 1) < (hi - 1) - lo;
}

/**
 * dma_fifo_init: initialize the fifo to a valid but inoperative state
 * @fifo: address of in-place "struct dma_fifo" object
 */
void dma_fifo_init(struct dma_fifo *fifo)
{
        memset(fifo, 0, sizeof(*fifo));
        INIT_LIST_HEAD(&fifo->pending);
}

/**
 * dma_fifo_alloc - initialize and allocate dma_fifo
 * @fifo: address of in-place "struct dma_fifo" object
 * @size: 'apparent' size, in bytes, of fifo
 * @align: dma alignment to maintain (should be at least cpu cache alignment),
 *         must be power of 2
 * @tx_limit: maximum # of bytes transmissable per dma (rounded down to
 *            multiple of alignment, but at least align size)
 * @open_limit: maximum # of outstanding dma transactions allowed
 * @gfp_mask: get_free_pages mask, passed to kmalloc()
 *
 * The 'apparent' size will be rounded up to next greater aligned size.
 * Returns 0 if no error, otherwise an error code
 */
int dma_fifo_alloc(struct dma_fifo *fifo, int size, unsigned align,
                   int tx_limit, int open_limit, gfp_t gfp_mask)
{
        int capacity;

        if (!is_power_of_2(align) || size < 0)
                return -EINVAL;

        size = round_up(size, align);
        capacity = size + align * open_limit + align * DMA_FIFO_GUARD;
        fifo->data = kmalloc(capacity, gfp_mask);
        if (!fifo->data)
                return -ENOMEM;

        fifo->in = 0;
        fifo->out = 0;
        fifo->done = 0;
        fifo->size = size;
        fifo->avail = size;
        fifo->align = align;
        fifo->tx_limit = max_t(int, round_down(tx_limit, align), align);
        fifo->open = 0;
        fifo->open_limit = open_limit;
        fifo->guard = size + align * open_limit;
        fifo->capacity = capacity;
        fifo->corrupt = 0;

        return 0;
}

/**
 * dma_fifo_free - frees the fifo
 * @fifo: address of in-place "struct dma_fifo" to free
 *
 * Also reinits the fifo to a valid but inoperative state. This
 * allows the fifo to be reused with a different target requiring
 * different fifo parameters.
 */
void dma_fifo_free(struct dma_fifo *fifo)
{
        struct dma_pending *pending, *next;

        if (fifo->data == NULL)
                return;

        list_for_each_entry_safe(pending, next, &fifo->pending, link)
                list_del_init(&pending->link);
        kfree(fifo->data);
        fifo->data = NULL;
}

/**
 * dma_fifo_reset - dumps the fifo contents and reinits for reuse
 * @fifo: address of in-place "struct dma_fifo" to reset
 */
void dma_fifo_reset(struct dma_fifo *fifo)
{
        struct dma_pending *pending, *next;

        if (fifo->data == NULL)
                return;

        list_for_each_entry_safe(pending, next, &fifo->pending, link)
                list_del_init(&pending->link);
        fifo->in = 0;
        fifo->out = 0;
        fifo->done = 0;
        fifo->avail = fifo->size;
        fifo->open = 0;
        fifo->corrupt = 0;
}

/**
 * dma_fifo_in - copies data into the fifo
 * @fifo: address of in-place "struct dma_fifo" to write to
 * @src: buffer to copy from
 * @n: # of bytes to copy
 *
 * Returns the # of bytes actually copied, which can be less than requested if
 * the fifo becomes full. If < 0, return is error code.
 */
int dma_fifo_in(struct dma_fifo *fifo, const void *src, int n)
{
        int ofs, l;

        if (fifo->data == NULL)
                return -ENOENT;
        if (fifo->corrupt)
                return -ENXIO;

        if (n > fifo->avail)
                n = fifo->avail;
        if (n <= 0)
                return 0;

        ofs = fifo->in % fifo->capacity;
        l = min(n, fifo->capacity - ofs);
        memcpy(fifo->data + ofs, src, l);
        memcpy(fifo->data, src + l, n - l);

        if (FAIL(fifo, addr_check(fifo->done, fifo->in, fifo->in + n) ||
                 fifo->avail < n,
                 "fifo corrupt: in:%u out:%u done:%u n:%d avail:%d",
                 fifo->in, fifo->out, fifo->done, n, fifo->avail))
                return -ENXIO;

        fifo->in += n;
        fifo->avail -= n;

        df_trace("in:%u out:%u done:%u n:%d avail:%d", fifo->in, fifo->out,
                 fifo->done, n, fifo->avail);

        return n;
}

/**
 * dma_fifo_out_pend - gets address/len of next avail read and marks as pended
 * @fifo: address of in-place "struct dma_fifo" to read from
 * @pended: address of structure to fill with read address/len
 *          The data/len fields will be NULL/0 if no dma is pended.
 *
 * Returns the # of used bytes remaining in fifo (ie, if > 0, more data
 * remains in the fifo that was not pended). If < 0, return is error code.
 */
int dma_fifo_out_pend(struct dma_fifo *fifo, struct dma_pending *pended)
{
        unsigned len, n, ofs, l, limit;

        if (fifo->data == NULL)
                return -ENOENT;
        if (fifo->corrupt)
                return -ENXIO;

        pended->len = 0;
        pended->data = NULL;
        pended->out = fifo->out;

        len = fifo->in - fifo->out;
        if (!len)
                return -ENODATA;
        if (fifo->open == fifo->open_limit)
                return -EAGAIN;

        n = len;
        ofs = fifo->out % fifo->capacity;
        l = fifo->capacity - ofs;
        limit = min_t(unsigned, l, fifo->tx_limit);
        if (n > limit) {
                n = limit;
                fifo->out += limit;
        } else if (ofs + n > fifo->guard) {
                fifo->out += l;
                fifo->in = fifo->out;
        } else {
                fifo->out += round_up(n, fifo->align);
                fifo->in = fifo->out;
        }

        df_trace("in: %u out: %u done: %u n: %d len: %u avail: %d", fifo->in,
                 fifo->out, fifo->done, n, len, fifo->avail);

        pended->len = n;
        pended->data = fifo->data + ofs;
        pended->next = fifo->out;
        list_add_tail(&pended->link, &fifo->pending);
        ++fifo->open;

        if (FAIL(fifo, fifo->open > fifo->open_limit,
                 "past open limit:%d (limit:%d)",
                 fifo->open, fifo->open_limit))
                return -ENXIO;
        if (FAIL(fifo, fifo->out & (fifo->align - 1),
                 "fifo out unaligned:%u (align:%u)",
                 fifo->out, fifo->align))
                return -ENXIO;

        return len - n;
}

/**
 * dma_fifo_out_complete - marks pended dma as completed
 * @fifo: address of in-place "struct dma_fifo" which was read from
 * @complete: address of structure for previously pended dma to mark completed
 */
int dma_fifo_out_complete(struct dma_fifo *fifo, struct dma_pending *complete)
{
        struct dma_pending *pending, *next, *tmp;

        if (fifo->data == NULL)
                return -ENOENT;
        if (fifo->corrupt)
                return -ENXIO;
        if (list_empty(&fifo->pending) && fifo->open == 0)
                return -EINVAL;

        if (FAIL(fifo, list_empty(&fifo->pending) != (fifo->open == 0),
                 "pending list disagrees with open count:%d",
                 fifo->open))
                return -ENXIO;

        tmp = complete->data;
        *tmp = *complete;
        list_replace(&complete->link, &tmp->link);
        dp_mark_completed(tmp);

        /* Only update the fifo in the original pended order */
        list_for_each_entry_safe(pending, next, &fifo->pending, link) {
                if (!dp_is_completed(pending)) {
                        df_trace("still pending: saved out: %u len: %d",
                                 pending->out, pending->len);
                        break;
                }

                if (FAIL(fifo, pending->out != fifo->done ||
                         addr_check(fifo->in, fifo->done, pending->next),
                         "in:%u out:%u done:%u saved:%u next:%u",
                         fifo->in, fifo->out, fifo->done, pending->out,
                         pending->next))
                        return -ENXIO;

                list_del_init(&pending->link);
                fifo->done = pending->next;
                fifo->avail += pending->len;
                --fifo->open;

                df_trace("in: %u out: %u done: %u len: %u avail: %d", fifo->in,
                         fifo->out, fifo->done, pending->len, fifo->avail);
        }

        if (FAIL(fifo, fifo->open < 0, "open dma:%d < 0", fifo->open))
                return -ENXIO;
        if (FAIL(fifo, fifo->avail > fifo->size, "fifo avail:%d > size:%d",
                 fifo->avail, fifo->size))
                return -ENXIO;

        return 0;
}