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368fd0aa AG |
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 | */ | |
39 | struct task_barrier { | |
40 | unsigned int n; | |
41 | atomic_t count; | |
42 | struct semaphore enter_turnstile; | |
43 | struct semaphore exit_turnstile; | |
44 | }; | |
45 | ||
46 | static 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 | ||
55 | static 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 | ||
63 | static inline void task_barrier_add_task(struct task_barrier *tb) | |
64 | { | |
65 | tb->n++; | |
66 | } | |
67 | ||
68 | static 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 | */ | |
78 | static 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 | */ | |
92 | static 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 */ | |
101 | static inline void task_barrier_full(struct task_barrier *tb) | |
102 | { | |
103 | task_barrier_enter(tb); | |
104 | task_barrier_exit(tb); | |
105 | } | |
106 | ||
107 | #endif |