1 /* $NetBSD: task_barrier.h,v 1.2 2021/12/18 23:45:46 riastradh Exp $ */
2
3 /*
4 * Copyright 2019 Advanced Micro Devices, Inc.
5 *
6 * Permission is hereby granted, free of charge, to any person obtaining a
7 * copy of this software and associated documentation files (the "Software"),
8 * to deal in the Software without restriction, including without limitation
9 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
10 * and/or sell copies of the Software, and to permit persons to whom the
11 * Software is furnished to do so, subject to the following conditions:
12 *
13 * The above copyright notice and this permission notice shall be included in
14 * all copies or substantial portions of the Software.
15 *
16 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
17 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
18 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
19 * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
20 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
21 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
22 * OTHER DEALINGS IN THE SOFTWARE.
23 *
24 */
25 #include <linux/semaphore.h>
26 #include <linux/atomic.h>
27
28 /*
29 * Reusable 2 PHASE task barrier (randevouz point) implementation for N tasks.
30 * Based on the Little book of sempahores - https://greenteapress.com/wp/semaphores/
31 */
32
33
34
35 #ifndef DRM_TASK_BARRIER_H_
36 #define DRM_TASK_BARRIER_H_
37
38 /*
39 * Represents an instance of a task barrier.
40 */
41 struct task_barrier {
42 unsigned int n;
43 atomic_t count;
44 struct semaphore enter_turnstile;
45 struct semaphore exit_turnstile;
46 };
47
task_barrier_signal_turnstile(struct semaphore * turnstile,unsigned int n)48 static inline void task_barrier_signal_turnstile(struct semaphore *turnstile,
49 unsigned int n)
50 {
51 int i;
52
53 for (i = 0 ; i < n; i++)
54 up(turnstile);
55 }
56
task_barrier_init(struct task_barrier * tb)57 static inline void task_barrier_init(struct task_barrier *tb)
58 {
59 tb->n = 0;
60 atomic_set(&tb->count, 0);
61 sema_init(&tb->enter_turnstile, 0);
62 sema_init(&tb->exit_turnstile, 0);
63 }
64
task_barrier_add_task(struct task_barrier * tb)65 static inline void task_barrier_add_task(struct task_barrier *tb)
66 {
67 tb->n++;
68 }
69
task_barrier_rem_task(struct task_barrier * tb)70 static inline void task_barrier_rem_task(struct task_barrier *tb)
71 {
72 tb->n--;
73 }
74
75 /*
76 * Lines up all the threads BEFORE the critical point.
77 *
78 * When all thread passed this code the entry barrier is back to locked state.
79 */
task_barrier_enter(struct task_barrier * tb)80 static inline void task_barrier_enter(struct task_barrier *tb)
81 {
82 if (atomic_inc_return(&tb->count) == tb->n)
83 task_barrier_signal_turnstile(&tb->enter_turnstile, tb->n);
84
85 down(&tb->enter_turnstile);
86 }
87
88 /*
89 * Lines up all the threads AFTER the critical point.
90 *
91 * This function is used to avoid any one thread running ahead if the barrier is
92 * used repeatedly .
93 */
task_barrier_exit(struct task_barrier * tb)94 static inline void task_barrier_exit(struct task_barrier *tb)
95 {
96 if (atomic_dec_return(&tb->count) == 0)
97 task_barrier_signal_turnstile(&tb->exit_turnstile, tb->n);
98
99 down(&tb->exit_turnstile);
100 }
101
102 /* Convinieince function when nothing to be done in between entry and exit */
task_barrier_full(struct task_barrier * tb)103 static inline void task_barrier_full(struct task_barrier *tb)
104 {
105 task_barrier_enter(tb);
106 task_barrier_exit(tb);
107 }
108
109 #endif
110