/*-
 * Copyright (c) 2007-2009 Kip Macy <kmacy@freebsd.org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * $FreeBSD$
 *
 */

#ifndef _SYS_BUF_RING_H_
#define _SYS_BUF_RING_H_

#include <machine/cpu.h>
#include <sys/malloc.h>
#include <sys/systm.h>

#if defined(INVARIANTS) && !defined(DEBUG_BUFRING)
#define DEBUG_BUFRING 1
#endif

#ifdef DEBUG_BUFRING
#include <sys/lock.h>
#include <sys/mutex.h>
#endif

struct buf_ring {
        volatile uint32_t       br_prod_head;
        volatile uint32_t       br_prod_tail;
        int                     br_prod_size;
        int                     br_prod_mask;
        uint64_t                br_drops;
        volatile uint32_t       br_cons_head;
        volatile uint32_t       br_cons_tail;
        int                     br_cons_size;
        int                     br_cons_mask;
#ifdef DEBUG_BUFRING
        struct mtx              *br_lock;
#endif
        void                    *br_ring[0];
};

/*
 * multi-producer safe lock-free ring buffer enqueue
 *
 */
static __inline int
buf_ring_enqueue(struct buf_ring *br, void *buf)
{
        uint32_t prod_head, prod_next, cons_tail;
#ifdef DEBUG_BUFRING
        uint32_t i;
        for (i = br->br_cons_head; i != br->br_prod_head;
             i = ((i + 1) & br->br_cons_mask))
                if(br->br_ring[i] == buf)
                        panic("buf=%p already enqueue at %d prod=%d cons=%d",
                            buf, i, br->br_prod_tail, br->br_cons_tail);
#endif
        critical_enter();
        do {
                prod_head = br->br_prod_head;
                prod_next = (prod_head + 1) & br->br_prod_mask;
                cons_tail = br->br_cons_tail;

                if (prod_next == cons_tail) {
                        rmb();
                        if (prod_head == br->br_prod_head &&
                            cons_tail == br->br_cons_tail) {
                                br->br_drops++;
                                critical_exit();
                                return (ENOBUFS);
                        }
                        continue;
                }
        } while (!atomic_cmpset_acq_int(&br->br_prod_head, prod_head, prod_next));
#ifdef DEBUG_BUFRING
        if (br->br_ring[prod_head] != NULL)
                panic("dangling value in enqueue");
#endif
        br->br_ring[prod_head] = buf;

        /*
         * If there are other enqueues in progress
         * that preceded us, we need to wait for them
         * to complete
         */
        while (br->br_prod_tail != prod_head)
                cpu_spinwait();
        atomic_store_rel_int(&br->br_prod_tail, prod_next);
        critical_exit();
        return (0);
}

/*
 * multi-consumer safe dequeue
 *
 */
static __inline void *
buf_ring_dequeue_mc(struct buf_ring *br)
{
        uint32_t cons_head, cons_next;
        void *buf;

        critical_enter();
        do {
                cons_head = br->br_cons_head;
                cons_next = (cons_head + 1) & br->br_cons_mask;

                if (cons_head == br->br_prod_tail) {
                        critical_exit();
                        return (NULL);
                }
        } while (!atomic_cmpset_acq_int(&br->br_cons_head, cons_head, cons_next));

        buf = br->br_ring[cons_head];
#ifdef DEBUG_BUFRING
        br->br_ring[cons_head] = NULL;
#endif
        /*
         * If there are other dequeues in progress
         * that preceded us, we need to wait for them
         * to complete
         */
        while (br->br_cons_tail != cons_head)
                cpu_spinwait();

        atomic_store_rel_int(&br->br_cons_tail, cons_next);
        critical_exit();

        return (buf);
}

/*
 * single-consumer dequeue
 * use where dequeue is protected by a lock
 * e.g. a network driver's tx queue lock
 */
static __inline void *
buf_ring_dequeue_sc(struct buf_ring *br)
{
        uint32_t cons_head, cons_next;
#ifdef PREFETCH_DEFINED
        uint32_t cons_next_next;
#endif
        uint32_t prod_tail;
        void *buf;

        /*
         * This is a workaround to allow using buf_ring on ARM and ARM64.
         * ARM64TODO: Fix buf_ring in a generic way.
         * REMARKS: It is suspected that br_cons_head does not require
         *   load_acq operation, but this change was extensively tested
         *   and confirmed it's working. To be reviewed once again in
         *   FreeBSD-12.
         *
         * Preventing following situation:

         * Core(0) - buf_ring_enqueue()                                       Core(1) - buf_ring_dequeue_sc()
         * -----------------------------------------                                       ----------------------------------------------
         *
         *                                                                                cons_head = br->br_cons_head;
         * atomic_cmpset_acq_32(&br->br_prod_head, ...));
         *                                                                                buf = br->br_ring[cons_head];     <see <1>>
         * br->br_ring[prod_head] = buf;
         * atomic_store_rel_32(&br->br_prod_tail, ...);
         *                                                                                prod_tail = br->br_prod_tail;
         *                                                                                if (cons_head == prod_tail)
         *                                                                                        return (NULL);
         *                                                                                <condition is false and code uses invalid(old) buf>`
         *
         * <1> Load (on core 1) from br->br_ring[cons_head] can be reordered (speculative readed) by CPU.
         */
#if defined(__arm__) || defined(__aarch64__)
        cons_head = atomic_load_acq_32(&br->br_cons_head);
#else
        cons_head = br->br_cons_head;
#endif
        prod_tail = atomic_load_acq_32(&br->br_prod_tail);

        cons_next = (cons_head + 1) & br->br_cons_mask;
#ifdef PREFETCH_DEFINED
        cons_next_next = (cons_head + 2) & br->br_cons_mask;
#endif

        if (cons_head == prod_tail)
                return (NULL);

#ifdef PREFETCH_DEFINED
        if (cons_next != prod_tail) {
                prefetch(br->br_ring[cons_next]);
                if (cons_next_next != prod_tail)
                        prefetch(br->br_ring[cons_next_next]);
        }
#endif
        br->br_cons_head = cons_next;
        buf = br->br_ring[cons_head];

#ifdef DEBUG_BUFRING
        br->br_ring[cons_head] = NULL;
        if (!mtx_owned(br->br_lock))
                panic("lock not held on single consumer dequeue");
        if (br->br_cons_tail != cons_head)
                panic("inconsistent list cons_tail=%d cons_head=%d",
                    br->br_cons_tail, cons_head);
#endif
        br->br_cons_tail = cons_next;
        return (buf);
}

/*
 * single-consumer advance after a peek
 * use where it is protected by a lock
 * e.g. a network driver's tx queue lock
 */
static __inline void
buf_ring_advance_sc(struct buf_ring *br)
{
        uint32_t cons_head, cons_next;
        uint32_t prod_tail;

        cons_head = br->br_cons_head;
        prod_tail = br->br_prod_tail;

        cons_next = (cons_head + 1) & br->br_cons_mask;
        if (cons_head == prod_tail)
                return;
        br->br_cons_head = cons_next;
#ifdef DEBUG_BUFRING
        br->br_ring[cons_head] = NULL;
#endif
        br->br_cons_tail = cons_next;
}

/*
 * Used to return a buffer (most likely already there)
 * to the top od the ring. The caller should *not*
 * have used any dequeue to pull it out of the ring
 * but instead should have used the peek() function.
 * This is normally used where the transmit queue
 * of a driver is full, and an mubf must be returned.
 * Most likely whats in the ring-buffer is what
 * is being put back (since it was not removed), but
 * sometimes the lower transmit function may have
 * done a pullup or other function that will have
 * changed it. As an optimzation we always put it
 * back (since jhb says the store is probably cheaper),
 * if we have to do a multi-queue version we will need
 * the compare and an atomic.
 */
static __inline void
buf_ring_putback_sc(struct buf_ring *br, void *_new)
{
        KASSERT_FREEBSD(br->br_cons_head != br->br_prod_tail,
                ("Buf-Ring has none in putback")) ;
        br->br_ring[br->br_cons_head] = _new;
}

/*
 * return a pointer to the first entry in the ring
 * without modifying it, or NULL if the ring is empty
 * race-prone if not protected by a lock
 */
static __inline void *
buf_ring_peek(struct buf_ring *br)
{

#ifdef DEBUG_BUFRING
        if ((br->br_lock != NULL) && !mtx_owned(br->br_lock))
                panic("lock not held on single consumer dequeue");
#endif
        /*
         * I believe it is safe to not have a memory barrier
         * here because we control cons and tail is worst case
         * a lagging indicator so we worst case we might
         * return NULL immediately after a buffer has been enqueued
         */
        if (br->br_cons_head == br->br_prod_tail)
                return (NULL);

        return (br->br_ring[br->br_cons_head]);
}

static __inline void *
buf_ring_peek_clear_sc(struct buf_ring *br)
{
#ifdef DEBUG_BUFRING
        void *ret;

        if (!mtx_owned(br->br_lock))
                panic("lock not held on single consumer dequeue");
#endif
        /*
         * I believe it is safe to not have a memory barrier
         * here because we control cons and tail is worst case
         * a lagging indicator so we worst case we might
         * return NULL immediately after a buffer has been enqueued
         */
        if (br->br_cons_head == br->br_prod_tail)
                return (NULL);

#ifdef DEBUG_BUFRING
        /*
         * Single consumer, i.e. cons_head will not move while we are
         * running, so atomic_swap_ptr() is not necessary here.
         */
        ret = br->br_ring[br->br_cons_head];
        br->br_ring[br->br_cons_head] = NULL;
        return (ret);
#else
        return (br->br_ring[br->br_cons_head]);
#endif
}

static __inline int
buf_ring_full(struct buf_ring *br)
{

        return (((br->br_prod_head + 1) & br->br_prod_mask) == br->br_cons_tail);
}

static __inline int
buf_ring_empty(struct buf_ring *br)
{

        return (br->br_cons_head == br->br_prod_tail);
}

static __inline int
buf_ring_count(struct buf_ring *br)
{

        return ((br->br_prod_size + br->br_prod_tail - br->br_cons_tail)
            & br->br_prod_mask);
}

struct buf_ring *buf_ring_alloc(int count, struct malloc_type *type, int flags,
    struct mtx *);
void buf_ring_free(struct buf_ring *br, struct malloc_type *type);



#endif