1/*
  2 * Copyright 2019 Advanced Micro Devices, Inc.
  3 *
  4 * Permission is hereby granted, free of charge, to any person obtaining a
  5 * copy of this software and associated documentation files (the "Software"),
  6 * to deal in the Software without restriction, including without limitation
  7 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
  8 * and/or sell copies of the Software, and to permit persons to whom the
  9 * Software is furnished to do so, subject to the following conditions:
 10 *
 11 * The above copyright notice and this permission notice shall be included in
 12 * all copies or substantial portions of the Software.
 13 *
 14 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 15 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 16 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 17 * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
 18 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
 19 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 20 * OTHER DEALINGS IN THE SOFTWARE.
 21 *
 22 */
 23#include <linux/semaphore.h>
 24#include <linux/atomic.h>
 25
 26/*
 27 * Reusable 2 PHASE task barrier (randevouz point) implementation for N tasks.
 28 * Based on the Little book of sempahores - https://greenteapress.com/wp/semaphores/
 29 */
 30
 31
 32
 33#ifndef DRM_TASK_BARRIER_H_
 34#define DRM_TASK_BARRIER_H_
 35
 36/*
 37 * Represents an instance of a task barrier.
 38 */
 39struct task_barrier {
 40	unsigned int n;
 41	atomic_t count;
 42	struct semaphore enter_turnstile;
 43	struct semaphore exit_turnstile;
 44};
 45
 46static inline void task_barrier_signal_turnstile(struct semaphore *turnstile,
 47						 unsigned int n)
 48{
 49	int i;
 50
 51	for (i = 0 ; i < n; i++)
 52		up(turnstile);
 53}
 54
 55static inline void task_barrier_init(struct task_barrier *tb)
 56{
 57	tb->n = 0;
 58	atomic_set(&tb->count, 0);
 59	sema_init(&tb->enter_turnstile, 0);
 60	sema_init(&tb->exit_turnstile, 0);
 61}
 62
 63static inline void task_barrier_add_task(struct task_barrier *tb)
 64{
 65	tb->n++;
 66}
 67
 68static inline void task_barrier_rem_task(struct task_barrier *tb)
 69{
 70	tb->n--;
 71}
 72
 73/*
 74 * Lines up all the threads BEFORE the critical point.
 75 *
 76 * When all thread passed this code the entry barrier is back to locked state.
 77 */
 78static inline void task_barrier_enter(struct task_barrier *tb)
 79{
 80	if (atomic_inc_return(&tb->count) == tb->n)
 81		task_barrier_signal_turnstile(&tb->enter_turnstile, tb->n);
 82
 83	down(&tb->enter_turnstile);
 84}
 85
 86/*
 87 * Lines up all the threads AFTER the critical point.
 88 *
 89 * This function is used to avoid any one thread running ahead if the barrier is
 90 *  used repeatedly .
 91 */
 92static inline void task_barrier_exit(struct task_barrier *tb)
 93{
 94	if (atomic_dec_return(&tb->count) == 0)
 95		task_barrier_signal_turnstile(&tb->exit_turnstile, tb->n);
 96
 97	down(&tb->exit_turnstile);
 98}
 99
100/* Convinieince function when nothing to be done in between entry and exit */
101static inline void task_barrier_full(struct task_barrier *tb)
102{
103	task_barrier_enter(tb);
104	task_barrier_exit(tb);
105}
106
107#endif