1/*
  2 * Copyright (c) 2012-2016 VMware, Inc.  All rights reserved.
  3 *
  4 * This program is free software; you can redistribute it and/or
  5 * modify it under the terms of EITHER the GNU General Public License
  6 * version 2 as published by the Free Software Foundation or the BSD
  7 * 2-Clause License. This program is distributed in the hope that it
  8 * will be useful, but WITHOUT ANY WARRANTY; WITHOUT EVEN THE IMPLIED
  9 * WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
 10 * See the GNU General Public License version 2 for more details at
 11 * http://www.gnu.org/licenses/old-licenses/gpl-2.0.en.html.
 12 *
 13 * You should have received a copy of the GNU General Public License
 14 * along with this program available in the file COPYING in the main
 15 * directory of this source tree.
 16 *
 17 * The BSD 2-Clause License
 18 *
 19 *     Redistribution and use in source and binary forms, with or
 20 *     without modification, are permitted provided that the following
 21 *     conditions are met:
 22 *
 23 *      - Redistributions of source code must retain the above
 24 *        copyright notice, this list of conditions and the following
 25 *        disclaimer.
 26 *
 27 *      - Redistributions in binary form must reproduce the above
 28 *        copyright notice, this list of conditions and the following
 29 *        disclaimer in the documentation and/or other materials
 30 *        provided with the distribution.
 31 *
 32 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 33 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 34 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 35 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 36 * COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
 37 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 38 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 39 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 40 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 41 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 42 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 43 * OF THE POSSIBILITY OF SUCH DAMAGE.
 44 */
 45
 46#ifndef __PVRDMA_RING_H__
 47#define __PVRDMA_RING_H__
 48
 49#include <linux/types.h>
 50
 51#define PVRDMA_INVALID_IDX	-1	/* Invalid index. */
 52
 53struct pvrdma_ring {
 54	atomic_t prod_tail;	/* Producer tail. */
 55	atomic_t cons_head;	/* Consumer head. */
 56};
 57
 58struct pvrdma_ring_state {
 59	struct pvrdma_ring tx;	/* Tx ring. */
 60	struct pvrdma_ring rx;	/* Rx ring. */
 61};
 62
 63static inline int pvrdma_idx_valid(__u32 idx, __u32 max_elems)
 64{
 65	/* Generates fewer instructions than a less-than. */
 66	return (idx & ~((max_elems << 1) - 1)) == 0;
 67}
 68
 69static inline __s32 pvrdma_idx(atomic_t *var, __u32 max_elems)
 70{
 71	const unsigned int idx = atomic_read(var);
 72
 73	if (pvrdma_idx_valid(idx, max_elems))
 74		return idx & (max_elems - 1);
 75	return PVRDMA_INVALID_IDX;
 76}
 77
 78static inline void pvrdma_idx_ring_inc(atomic_t *var, __u32 max_elems)
 79{
 80	__u32 idx = atomic_read(var) + 1;	/* Increment. */
 81
 82	idx &= (max_elems << 1) - 1;		/* Modulo size, flip gen. */
 83	atomic_set(var, idx);
 84}
 85
 86static inline __s32 pvrdma_idx_ring_has_space(const struct pvrdma_ring *r,
 87					      __u32 max_elems, __u32 *out_tail)
 88{
 89	const __u32 tail = atomic_read(&r->prod_tail);
 90	const __u32 head = atomic_read(&r->cons_head);
 91
 92	if (pvrdma_idx_valid(tail, max_elems) &&
 93	    pvrdma_idx_valid(head, max_elems)) {
 94		*out_tail = tail & (max_elems - 1);
 95		return tail != (head ^ max_elems);
 96	}
 97	return PVRDMA_INVALID_IDX;
 98}
 99
100static inline __s32 pvrdma_idx_ring_has_data(const struct pvrdma_ring *r,
101					     __u32 max_elems, __u32 *out_head)
102{
103	const __u32 tail = atomic_read(&r->prod_tail);
104	const __u32 head = atomic_read(&r->cons_head);
105
106	if (pvrdma_idx_valid(tail, max_elems) &&
107	    pvrdma_idx_valid(head, max_elems)) {
108		*out_head = head & (max_elems - 1);
109		return tail != head;
110	}
111	return PVRDMA_INVALID_IDX;
112}
113
114#endif /* __PVRDMA_RING_H__ */