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 (rendez-vous point) implementation for N tasks. |
28 | * Based on the Little book of semaphores - 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(sem: turnstile); |
53 | } |
54 | |
55 | static inline void task_barrier_init(struct task_barrier *tb) |
56 | { |
57 | tb->n = 0; |
58 | atomic_set(v: &tb->count, i: 0); |
59 | sema_init(sem: &tb->enter_turnstile, val: 0); |
60 | sema_init(sem: &tb->exit_turnstile, val: 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(v: &tb->count) == tb->n) |
81 | task_barrier_signal_turnstile(turnstile: &tb->enter_turnstile, n: tb->n); |
82 | |
83 | down(sem: &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(v: &tb->count) == 0) |
95 | task_barrier_signal_turnstile(turnstile: &tb->exit_turnstile, n: tb->n); |
96 | |
97 | down(sem: &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 |
108 | |