linux-imx

/*

 * Fence mechanism for dma-buf and to allow for asynchronous dma access

 *

 * Copyright (C) 2012 Canonical Ltd

 * Copyright (C) 2012 Texas Instruments

 *

 * Authors:

 * Rob Clark <robdclark@gmail.com>

 * Maarten Lankhorst <maarten.lankhorst@canonical.com>

 *

 * This program is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 as published by

 * the Free Software Foundation.

 *

 * This program is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for

 * more details.

 */

​

#include <linux/slab.h>

#include <linux/export.h>

#include <linux/atomic.h>

#include <linux/dma-fence.h>

#include <linux/sched/signal.h>

​

#define CREATE_TRACE_POINTS

#include <trace/events/dma_fence.h>

​

EXPORT_TRACEPOINT_SYMBOL(dma_fence_emit);

EXPORT_TRACEPOINT_SYMBOL(dma_fence_enable_signal);

​

static DEFINE_SPINLOCK(dma_fence_stub_lock);

static struct dma_fence dma_fence_stub;

​

/*

 * fence context counter: each execution context should have its own

 * fence context, this allows checking if fences belong to the same

 * context or not. One device can have multiple separate contexts,

 * and they're used if some engine can run independently of another.

 */

static atomic64_t dma_fence_context_counter = ATOMIC64_INIT(1);

​

/**

 * DOC: DMA fences overview

 *

 * DMA fences, represented by &struct dma_fence, are the kernel internal

 * synchronization primitive for DMA operations like GPU rendering, video

 * encoding/decoding, or displaying buffers on a screen.

 *

 * A fence is initialized using dma_fence_init() and completed using

 * dma_fence_signal(). Fences are associated with a context, allocated through

 * dma_fence_context_alloc(), and all fences on the same context are

 * fully ordered.

 *

 * Since the purposes of fences is to facilitate cross-device and

 * cross-application synchronization, there's multiple ways to use one:

 *

 * - Individual fences can be exposed as a &sync_file, accessed as a file

 *   descriptor from userspace, created by calling sync_file_create(). This is

 *   called explicit fencing, since userspace passes around explicit

 *   synchronization points.

 *