LXR linux/include/drm/task

   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 */
  39struct task_barrier {
  40        unsigned int n;
  41        atomic_t count;
  42        struct semaphore enter_turnstile;
  43        struct semaphore exit_turnstile;
  44};
  45
  46static 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
  55static 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
  63static inline void task_barrier_add_task(struct task_barrier *tb)
  64{
  65        tb->n++;
  66}
  67
  68static 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 */
  78static 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 */
  92static 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 */
 101static 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