drivers/dma-buf/dma-fence-unwrap.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * dma-fence-util: misc functions for dma_fence objects
 *
 * Copyright (C) 2022 Advanced Micro Devices, Inc.
 * Authors:
 *	Christian König <christian.koenig@amd.com>
 */

#include <linux/dma-fence.h>
#include <linux/dma-fence-array.h>
#include <linux/dma-fence-chain.h>
#include <linux/dma-fence-unwrap.h>
#include <linux/slab.h>
#include <linux/sort.h>

/* Internal helper to start new array iteration, don't use directly */
static struct dma_fence *
__dma_fence_unwrap_array(struct dma_fence_unwrap *cursor)
{
	cursor->array = dma_fence_chain_contained(cursor->chain);
	cursor->index = 0;
	return dma_fence_array_first(cursor->array);
}

/**
 * dma_fence_unwrap_first - return the first fence from fence containers
 * @head: the entrypoint into the containers
 * @cursor: current position inside the containers
 *
 * Unwraps potential dma_fence_chain/dma_fence_array containers and return the
 * first fence.
 */
struct dma_fence *dma_fence_unwrap_first(struct dma_fence *head,
					 struct dma_fence_unwrap *cursor)
{
	cursor->chain = dma_fence_get(head);
	return __dma_fence_unwrap_array(cursor);
}
EXPORT_SYMBOL_GPL(dma_fence_unwrap_first);

/**
 * dma_fence_unwrap_next - return the next fence from a fence containers
 * @cursor: current position inside the containers
 *
 * Continue unwrapping the dma_fence_chain/dma_fence_array containers and return
 * the next fence from them.
 */
struct dma_fence *dma_fence_unwrap_next(struct dma_fence_unwrap *cursor)
{
	struct dma_fence *tmp;

	++cursor->index;
	tmp = dma_fence_array_next(cursor->array, cursor->index);
	if (tmp)
		return tmp;

	cursor->chain = dma_fence_chain_walk(cursor->chain);
	return __dma_fence_unwrap_array(cursor);
}
EXPORT_SYMBOL_GPL(dma_fence_unwrap_next);


static int fence_cmp(const void *_a, const void *_b)
{
	struct dma_fence *a = *(struct dma_fence **)_a;
	struct dma_fence *b = *(struct dma_fence **)_b;

	if (a->context < b->context)
		return -1;
	else if (a->context > b->context)
		return 1;

	if (dma_fence_is_later(b, a))
		return 1;
	else if (dma_fence_is_later(a, b))
		return -1;

	return 0;
}

/**
 * dma_fence_dedup_array - Sort and deduplicate an array of dma_fence pointers
 * @fences:     Array of dma_fence pointers to be deduplicated
 * @num_fences: Number of entries in the @fences array
 *
 * Sorts the input array by context, then removes duplicate
 * fences with the same context, keeping only the most recent one.
 *
 * The array is modified in-place and unreferenced duplicate fences are released
 * via dma_fence_put(). The function returns the new number of fences after
 * deduplication.
 *
 * Return: Number of unique fences remaining in the array.
 */
int dma_fence_dedup_array(struct dma_fence **fences, int num_fences)
{
	int i, j;

	sort(fences, num_fences, sizeof(*fences), fence_cmp, NULL);

	/*
	 * Only keep the most recent fence for each context.
	 */
	j = 0;
	for (i = 1; i < num_fences; i++) {
		if (fences[i]->context == fences[j]->context)
			dma_fence_put(fences[i]);
		else
			fences[++j] = fences[i];
	}

	return ++j;
}
EXPORT_SYMBOL_GPL(dma_fence_dedup_array);

/* Implementation for the dma_fence_merge() marco, don't use directly */
struct dma_fence *__dma_fence_unwrap_merge(unsigned int num_fences,
					   struct dma_fence **fences,
					   struct dma_fence_unwrap *iter)
{
	struct dma_fence *tmp, *unsignaled = NULL, **array;
	struct dma_fence_array *result;
	ktime_t timestamp;
	int i, count;

	count = 0;
	timestamp = ns_to_ktime(0);
	for (i = 0; i < num_fences; ++i) {
		dma_fence_unwrap_for_each(tmp, &iter[i], fences[i]) {
			if (!dma_fence_is_signaled(tmp)) {
				dma_fence_put(unsignaled);
				unsignaled = dma_fence_get(tmp);
				++count;
			} else {
				ktime_t t = dma_fence_timestamp(tmp);

				if (ktime_after(t, timestamp))
					timestamp = t;
			}
		}
	}

	/*
	 * If we couldn't find a pending fence just return a private signaled
	 * fence with the timestamp of the last signaled one.
	 *
	 * Or if there was a single unsignaled fence left we can return it
	 * directly and early since that is a major path on many workloads.
	 */
	if (count == 0)
		return dma_fence_allocate_private_stub(timestamp);
	else if (count == 1)
		return unsignaled;

	dma_fence_put(unsignaled);

	array = kmalloc_array(count, sizeof(*array), GFP_KERNEL);
	if (!array)
		return NULL;

	count = 0;
	for (i = 0; i < num_fences; ++i) {
		dma_fence_unwrap_for_each(tmp, &iter[i], fences[i]) {
			if (!dma_fence_is_signaled(tmp)) {
				array[count++] = dma_fence_get(tmp);
			} else {
				ktime_t t = dma_fence_timestamp(tmp);

				if (ktime_after(t, timestamp))
					timestamp = t;
			}
		}
	}

	if (count == 0 || count == 1)
		goto return_fastpath;

	count = dma_fence_dedup_array(array, count);

	if (count > 1) {
		result = dma_fence_array_create(count, array,
						dma_fence_context_alloc(1),
						1, false);
		if (!result) {
			for (i = 0; i < count; i++)
				dma_fence_put(array[i]);
			tmp = NULL;
			goto return_tmp;
		}
		return &result->base;
	}

return_fastpath:
	if (count == 0)
		tmp = dma_fence_allocate_private_stub(timestamp);
	else
		tmp = array[0];

return_tmp:
	kfree(array);
	return tmp;
}
EXPORT_SYMBOL_GPL(__dma_fence_unwrap_merge);