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| 2 | * Copyright 2019 Advanced Micro Devices, Inc.
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| 3 | *
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| 4 | * Permission is hereby granted, free of charge, to any person obtaining a
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| 5 | * copy of this software and associated documentation files (the "Software"),
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| 6 | * to deal in the Software without restriction, including without limitation
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| 7 | * the rights to use, copy, modify, merge, publish, distribute, sublicense,
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| 8 | * and/or sell copies of the Software, and to permit persons to whom the
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| 9 | * Software is furnished to do so, subject to the following conditions:
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| 10 | *
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| 11 | * The above copyright notice and this permission notice shall be included in
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| 12 | * all copies or substantial portions of the Software.
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| 13 | *
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| 14 | * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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| 15 | * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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| 16 | * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
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| 17 | * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
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| 18 | * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
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| 19 | * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
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| 20 | * OTHER DEALINGS IN THE SOFTWARE.
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| 21 | *
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| 22 |
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| 23 | #include <linux/semaphore.h>
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| 24 | #include <linux/atomic.h>
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| 25 |
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| 26 | |
| 27 | * Reusable 2 PHASE task barrier (rendez-vous point) implementation for N tasks.
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| 28 | * Based on the Little book of semaphores - https://greenteapress.com/wp/semaphores/
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| 29 |
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| 30 |
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| 31 |
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| 32 |
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| 33 | #ifndef DRM_TASK_BARRIER_H_
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| 34 | #define DRM_TASK_BARRIER_H_
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| 35 |
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| 36 | |
| 37 | * Represents an instance of a task barrier.
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| 38 |
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| 39 | struct task_barrier {
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| 40 | unsigned int n;
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| 41 | atomic_t count;
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| 42 | struct semaphore enter_turnstile;
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| 43 | struct semaphore exit_turnstile;
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| 44 | };
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| 45 |
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| 46 | static inline void task_barrier_signal_turnstile(struct semaphore *turnstile,
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| 47 | unsigned int n)
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| 48 | {
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| 49 | int i;
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| 50 |
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| 51 | for (i = 0 ; i < n; i++)
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| 52 | up(turnstile);
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| 53 | }
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| 54 |
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| 55 | static inline void task_barrier_init(struct task_barrier *tb)
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| 56 | {
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| 57 | tb->n = 0;
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| 58 | atomic_set(&tb->count, 0);
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| 59 | sema_init(&tb->enter_turnstile, 0);
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| 60 | sema_init(&tb->exit_turnstile, 0);
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| 61 | }
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| 62 |
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| 63 | static inline void task_barrier_add_task(struct task_barrier *tb)
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| 64 | {
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| 65 | tb->n++;
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| 66 | }
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| 67 |
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| 68 | static inline void task_barrier_rem_task(struct task_barrier *tb)
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| 69 | {
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| 70 | tb->n--;
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| 71 | }
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| 72 |
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| 73 | |
| 74 | * Lines up all the threads BEFORE the critical point.
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| 75 | *
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| 76 | * When all thread passed this code the entry barrier is back to locked state.
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| 77 |
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| 78 | static inline void task_barrier_enter(struct task_barrier *tb)
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| 79 | {
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| 80 | if (atomic_inc_return(&tb->count) == tb->n)
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| 81 | task_barrier_signal_turnstile(&tb->enter_turnstile, tb->n);
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| 82 |
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| 83 | down(&tb->enter_turnstile);
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| 84 | }
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| 85 |
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| 86 | |
| 87 | * Lines up all the threads AFTER the critical point.
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| 88 | *
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| 89 | * This function is used to avoid any one thread running ahead if the barrier is
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| 90 | * used repeatedly .
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| 91 |
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| 92 | static inline void task_barrier_exit(struct task_barrier *tb)
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| 93 | {
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| 94 | if (atomic_dec_return(&tb->count) == 0)
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| 95 | task_barrier_signal_turnstile(&tb->exit_turnstile, tb->n);
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| 96 |
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| 97 | down(&tb->exit_turnstile);
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| 98 | }
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| 99 |
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| 100 |
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| 101 | static inline void task_barrier_full(struct task_barrier *tb)
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| 102 | {
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| 103 | task_barrier_enter(tb);
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| 104 | task_barrier_exit(tb);
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| 105 | }
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| 106 |
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| 107 | #endif
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