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drm: Add Reusable task barrier.

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It is used to synchronize N threads at a rendevouz point before execution
of critical code that has to be started by all the threads at approximatly
the same time.

v2: Remove mention of reset use case, improve doc.

Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Reviewed-by: Le Ma <Le.Ma@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
This commit is contained in:
Andrey Grodzovsky 2019-12-06 12:26:33 -05:00 committed by Alex Deucher
parent 041a62bc06
commit 368fd0aad1
1 changed files with 107 additions and 0 deletions
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107
include/drm/task_barrier.h Normal file
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/*
* Copyright 2019 Advanced Micro Devices, Inc.
*
* Permission is hereby granted, free of charge, to any person obtaining a
* copy of this software and associated documentation files (the "Software"),
* to deal in the Software without restriction, including without limitation
* the rights to use, copy, modify, merge, publish, distribute, sublicense,
* and/or sell copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
* OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
* ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
* OTHER DEALINGS IN THE SOFTWARE.
*
*/
#include <linux/semaphore.h>
#include <linux/atomic.h>
/*
* Reusable 2 PHASE task barrier (randevouz point) implementation for N tasks.
* Based on the Little book of sempahores - https://greenteapress.com/wp/semaphores/
*/
#ifndef DRM_TASK_BARRIER_H_
#define DRM_TASK_BARRIER_H_
/*
* Represents an instance of a task barrier.
*/
struct task_barrier {
unsigned int n;
atomic_t count;
struct semaphore enter_turnstile;
struct semaphore exit_turnstile;
};
static inline void task_barrier_signal_turnstile(struct semaphore *turnstile,
unsigned int n)
{
int i;
for (i = 0 ; i < n; i++)
up(turnstile);
}
static inline void task_barrier_init(struct task_barrier *tb)
{
tb->n = 0;
atomic_set(&tb->count, 0);
sema_init(&tb->enter_turnstile, 0);
sema_init(&tb->exit_turnstile, 0);
}
static inline void task_barrier_add_task(struct task_barrier *tb)
{
tb->n++;
}
static inline void task_barrier_rem_task(struct task_barrier *tb)
{
tb->n--;
}
/*
* Lines up all the threads BEFORE the critical point.
*
* When all thread passed this code the entry barrier is back to locked state.
*/
static inline void task_barrier_enter(struct task_barrier *tb)
{
if (atomic_inc_return(&tb->count) == tb->n)
task_barrier_signal_turnstile(&tb->enter_turnstile, tb->n);
down(&tb->enter_turnstile);
}
/*
* Lines up all the threads AFTER the critical point.
*
* This function is used to avoid any one thread running ahead if the barrier is
* used repeatedly .
*/
static inline void task_barrier_exit(struct task_barrier *tb)
{
if (atomic_dec_return(&tb->count) == 0)
task_barrier_signal_turnstile(&tb->exit_turnstile, tb->n);
down(&tb->exit_turnstile);
}
/* Convinieince function when nothing to be done in between entry and exit */
static inline void task_barrier_full(struct task_barrier *tb)
{
task_barrier_enter(tb);
task_barrier_exit(tb);
}
#endif