/* SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 2010-2020 Intel Corporation
 * Copyright (c) 2007-2009 Kip Macy kmacy@freebsd.org
 * All rights reserved.
 * Derived from FreeBSD's bufring.h
 * Used as BSD-3 Licensed with permission from Kip Macy.
 */

#ifndef _RTE_RING_HTS_ELEM_PVT_H_
#define _RTE_RING_HTS_ELEM_PVT_H_

/**
 * @file rte_ring_hts_elem_pvt.h
 * It is not recommended to include this file directly,
 * include <rte_ring.h> instead.
 * Contains internal helper functions for head/tail sync (HTS) ring mode.
 * For more information please refer to <rte_ring_hts.h>.
 */

/**
 * @internal update tail with new value.
 */
static __rte_always_inline void
__rte_ring_hts_update_tail(struct rte_ring_hts_headtail *ht, uint32_t old_tail,
        uint32_t num, uint32_t enqueue)
{
        uint32_t tail;

        RTE_SET_USED(enqueue);

        tail = old_tail + num;
        __atomic_store_n(&ht->ht.pos.tail, tail, __ATOMIC_RELEASE);
}

/**
 * @internal waits till tail will become equal to head.
 * Means no writer/reader is active for that ring.
 * Suppose to work as serialization point.
 */
static __rte_always_inline void
__rte_ring_hts_head_wait(const struct rte_ring_hts_headtail *ht,
                union __rte_ring_hts_pos *p)
{
        while (p->pos.head != p->pos.tail) {
                rte_pause();
                p->raw = __atomic_load_n(&ht->ht.raw, __ATOMIC_ACQUIRE);
        }
}

/**
 * @internal This function updates the producer head for enqueue
 */
static __rte_always_inline unsigned int
__rte_ring_hts_move_prod_head(struct rte_ring *r, unsigned int num,
        enum rte_ring_queue_behavior behavior, uint32_t *old_head,
        uint32_t *free_entries)
{
        uint32_t n;
        union __rte_ring_hts_pos np, op;

        const uint32_t capacity = r->capacity;

        op.raw = __atomic_load_n(&r->hts_prod.ht.raw, __ATOMIC_ACQUIRE);

        do {
                /* Reset n to the initial burst count */
                n = num;

                /*
                 * wait for tail to be equal to head,
                 * make sure that we read prod head/tail *before*
                 * reading cons tail.
                 */
                __rte_ring_hts_head_wait(&r->hts_prod, &op);

                /*
                 *  The subtraction is done between two unsigned 32bits value
                 * (the result is always modulo 32 bits even if we have
                 * *old_head > cons_tail). So 'free_entries' is always between 0
                 * and capacity (which is < size).
                 */
                *free_entries = capacity + r->cons.tail - op.pos.head;

                /* check that we have enough room in ring */
                if (unlikely(n > *free_entries))
                        n = (behavior == RTE_RING_QUEUE_FIXED) ?
                                        0 : *free_entries;

                if (n == 0)
                        break;

                np.pos.tail = op.pos.tail;
                np.pos.head = op.pos.head + n;

        /*
         * this CAS(ACQUIRE, ACQUIRE) serves as a hoist barrier to prevent:
         *  - OOO reads of cons tail value
         *  - OOO copy of elems from the ring
         */
        } while (__atomic_compare_exchange_n(&r->hts_prod.ht.raw,
                        &op.raw, np.raw,
                        0, __ATOMIC_ACQUIRE, __ATOMIC_ACQUIRE) == 0);

        *old_head = op.pos.head;
        return n;
}

/**
 * @internal This function updates the consumer head for dequeue
 */
static __rte_always_inline unsigned int
__rte_ring_hts_move_cons_head(struct rte_ring *r, unsigned int num,
        enum rte_ring_queue_behavior behavior, uint32_t *old_head,
        uint32_t *entries)
{
        uint32_t n;
        union __rte_ring_hts_pos np, op;

        op.raw = __atomic_load_n(&r->hts_cons.ht.raw, __ATOMIC_ACQUIRE);

        /* move cons.head atomically */
        do {
                /* Restore n as it may change every loop */
                n = num;

                /*
                 * wait for tail to be equal to head,
                 * make sure that we read cons head/tail *before*
                 * reading prod tail.
                 */
                __rte_ring_hts_head_wait(&r->hts_cons, &op);

                /* The subtraction is done between two unsigned 32bits value
                 * (the result is always modulo 32 bits even if we have
                 * cons_head > prod_tail). So 'entries' is always between 0
                 * and size(ring)-1.
                 */
                *entries = r->prod.tail - op.pos.head;

                /* Set the actual entries for dequeue */
                if (n > *entries)
                        n = (behavior == RTE_RING_QUEUE_FIXED) ? 0 : *entries;

                if (unlikely(n == 0))
                        break;

                np.pos.tail = op.pos.tail;
                np.pos.head = op.pos.head + n;

        /*
         * this CAS(ACQUIRE, ACQUIRE) serves as a hoist barrier to prevent:
         *  - OOO reads of prod tail value
         *  - OOO copy of elems from the ring
         */
        } while (__atomic_compare_exchange_n(&r->hts_cons.ht.raw,
                        &op.raw, np.raw,
                        0, __ATOMIC_ACQUIRE, __ATOMIC_ACQUIRE) == 0);

        *old_head = op.pos.head;
        return n;
}

/**
 * @internal Enqueue several objects on the HTS ring.
 *
 * @param r
 *   A pointer to the ring structure.
 * @param obj_table
 *   A pointer to a table of objects.
 * @param esize
 *   The size of ring element, in bytes. It must be a multiple of 4.
 *   This must be the same value used while creating the ring. Otherwise
 *   the results are undefined.
 * @param n
 *   The number of objects to add in the ring from the obj_table.
 * @param behavior
 *   RTE_RING_QUEUE_FIXED:    Enqueue a fixed number of items from a ring
 *   RTE_RING_QUEUE_VARIABLE: Enqueue as many items as possible from ring
 * @param free_space
 *   returns the amount of space after the enqueue operation has finished
 * @return
 *   Actual number of objects enqueued.
 *   If behavior == RTE_RING_QUEUE_FIXED, this will be 0 or n only.
 */
static __rte_always_inline unsigned int
__rte_ring_do_hts_enqueue_elem(struct rte_ring *r, const void *obj_table,
        uint32_t esize, uint32_t n, enum rte_ring_queue_behavior behavior,
        uint32_t *free_space)
{
        uint32_t free, head;

        n =  __rte_ring_hts_move_prod_head(r, n, behavior, &head, &free);

        if (n != 0) {
                __rte_ring_enqueue_elems(r, head, obj_table, esize, n);
                __rte_ring_hts_update_tail(&r->hts_prod, head, n, 1);
        }

        if (free_space != NULL)
                *free_space = free - n;
        return n;
}

/**
 * @internal Dequeue several objects from the HTS ring.
 *
 * @param r
 *   A pointer to the ring structure.
 * @param obj_table
 *   A pointer to a table of objects.
 * @param esize
 *   The size of ring element, in bytes. It must be a multiple of 4.
 *   This must be the same value used while creating the ring. Otherwise
 *   the results are undefined.
 * @param n
 *   The number of objects to pull from the ring.
 * @param behavior
 *   RTE_RING_QUEUE_FIXED:    Dequeue a fixed number of items from a ring
 *   RTE_RING_QUEUE_VARIABLE: Dequeue as many items as possible from ring
 * @param available
 *   returns the number of remaining ring entries after the dequeue has finished
 * @return
 *   - Actual number of objects dequeued.
 *     If behavior == RTE_RING_QUEUE_FIXED, this will be 0 or n only.
 */
static __rte_always_inline unsigned int
__rte_ring_do_hts_dequeue_elem(struct rte_ring *r, void *obj_table,
        uint32_t esize, uint32_t n, enum rte_ring_queue_behavior behavior,
        uint32_t *available)
{
        uint32_t entries, head;

        n = __rte_ring_hts_move_cons_head(r, n, behavior, &head, &entries);

        if (n != 0) {
                __rte_ring_dequeue_elems(r, head, obj_table, esize, n);
                __rte_ring_hts_update_tail(&r->hts_cons, head, n, 0);
        }

        if (available != NULL)
                *available = entries - n;
        return n;
}

#endif /* _RTE_RING_HTS_ELEM_PVT_H_ */