1. 根目录:
2. sound
3. firewire
4. packets-buffer.c

/*
 * helpers for managing a buffer for many packets
 *
 * Copyright (c) Clemens Ladisch <clemens@ladisch.de>
 * Licensed under the terms of the GNU General Public License, version 2.
 */

#include <linux/firewire.h>
#include <linux/slab.h>
#include "packets-buffer.h"

/**
 * iso_packets_buffer_init - allocates the memory for packets
 * @b: the buffer structure to initialize
 * @unit: the device at the other end of the stream
 * @count: the number of packets
 * @packet_size: the (maximum) size of a packet, in bytes
 * @direction: %DMA_TO_DEVICE or %DMA_FROM_DEVICE
 */
int iso_packets_buffer_init(struct iso_packets_buffer *b, struct fw_unit *unit,
			    unsigned int count, unsigned int packet_size,
			    enum dma_data_direction direction)
{
	unsigned int packets_per_page, pages;
	unsigned int i, page_index, offset_in_page;
	void *p;
	int err;

	b->packets = kmalloc(count * sizeof(*b->packets), GFP_KERNEL);
	if (!b->packets) {
		err = -ENOMEM;
		goto error;
	}

	packet_size = L1_CACHE_ALIGN(packet_size);
	packets_per_page = PAGE_SIZE / packet_size;
	if (WARN_ON(!packets_per_page)) {
		err = -EINVAL;
		goto error;
	}
	pages = DIV_ROUND_UP(count, packets_per_page);

	err = fw_iso_buffer_init(&b->iso_buffer, fw_parent_device(unit)->card,
				 pages, direction);
	if (err < 0)
		goto err_packets;

	for (i = 0; i < count; ++i) {
		page_index = i / packets_per_page;
		p = page_address(b->iso_buffer.pages[page_index]);
		offset_in_page = (i % packets_per_page) * packet_size;
		b->packets[i].buffer = p + offset_in_page;
		b->packets[i].offset = page_index * PAGE_SIZE + offset_in_page;
	}

	return 0;

err_packets:
	kfree(b->packets);
error:
	return err;
}
EXPORT_SYMBOL(iso_packets_buffer_init);

/**
 * iso_packets_buffer_destroy - frees packet buffer resources
 * @b: the buffer structure to free
 * @unit: the device at the other end of the stream
 */
void iso_packets_buffer_destroy(struct iso_packets_buffer *b,
				struct fw_unit *unit)
{
	fw_iso_buffer_destroy(&b->iso_buffer, fw_parent_device(unit)->card);
	kfree(b->packets);
}
EXPORT_SYMBOL(iso_packets_buffer_destroy);