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      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 
     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 
     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 
     65 static inline void task_barrier_add_task(struct task_barrier *tb)
     66 {
     67 	tb->n++;
     68 }
     69 
     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  */
     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  */
     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 */
    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