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 108