/*
 *  Digital Audio (PCM) abstract layer
 *  Copyright (c) by Jaroslav Kysela <perex@perex.cz>
 *
 *
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation; either version 2 of the License, or
 *   (at your option) any later version.
 *
 *   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.
 *
 *   You should have received a copy of the GNU General Public License
 *   along with this program; if not, write to the Free Software
 *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
 *
 */

#include <asm/io.h>
#include <linux/time.h>
#include <linux/init.h>
#include <linux/moduleparam.h>
#include <sound/core.h>
#include <sound/pcm.h>
#include <sound/info.h>
#include <sound/initval.h>

static int preallocate_dma = 1;
module_param(preallocate_dma, int, 0444);
MODULE_PARM_DESC(preallocate_dma, "Preallocate DMA memory when the PCM devices are initialized.");

static int maximum_substreams = 4;
module_param(maximum_substreams, int, 0444);
MODULE_PARM_DESC(maximum_substreams, "Maximum substreams with preallocated DMA memory.");

static const size_t snd_minimum_buffer = 16384;


/*
 * try to allocate as the large pages as possible.
 * stores the resultant memory size in *res_size.
 *
 * the minimum size is snd_minimum_buffer.  it should be power of 2.
 */
static int preallocate_pcm_pages(struct snd_pcm_substream *substream, size_t size)
{
	struct snd_dma_buffer *dmab = &substream->dma_buffer;
	int err;

	/* already reserved? */
	if (snd_dma_get_reserved_buf(dmab, substream->dma_buf_id) > 0) {
		if (dmab->bytes >= size)
			return 0; /* yes */
		/* no, free the reserved block */
		snd_dma_free_pages(dmab);
		dmab->bytes = 0;
	}

	do {
		if ((err = snd_dma_alloc_pages(dmab->dev.type, dmab->dev.dev,
					       size, dmab)) < 0) {
			if (err != -ENOMEM)
				return err; /* fatal error */
		} else
			return 0;
		size >>= 1;
	} while (size >= snd_minimum_buffer);
	dmab->bytes = 0; /* tell error */
	return 0;
}

/*
 * release the preallocated buffer if not yet done.
 */
static void snd_pcm_lib_preallocate_dma_free(struct snd_pcm_substream *substream)
{
	if (substream->dma_buffer.area == NULL)
		return;
	if (substream->dma_buf_id)
		snd_dma_reserve_buf(&substream->dma_buffer, substream->dma_buf_id);
	else
		snd_dma_free_pages(&substream->dma_buffer);
	substream->dma_buffer.area = NULL;
}

/**
 * snd_pcm_lib_preallocate_free - release the preallocated buffer of the specified substream.
 * @substream: the pcm substream instance
 *
 * Releases the pre-allocated buffer of the given substream.
 *
 * Returns zero if successful, or a negative error code on failure.
 */
int snd_pcm_lib_preallocate_free(struct snd_pcm_substream *substream)
{
	snd_pcm_lib_preallocate_dma_free(substream);
#ifdef CONFIG_SND_VERBOSE_PROCFS
	snd_info_free_entry(substream->proc_prealloc_max_entry);
	substream->proc_prealloc_max_entry = NULL;
	snd_info_free_entry(substream->proc_prealloc_entry);
	substream->proc_prealloc_entry = NULL;
#endif
	return 0;
}

/**
 * snd_pcm_lib_preallocate_free_for_all - release all pre-allocated buffers on the pcm
 * @pcm: the pcm instance
 *
 * Releases all the pre-allocated buffers on the given pcm.
 *
 * Returns zero if successful, or a negative error code on failure.
 */
int snd_pcm_lib_preallocate_free_for_all(struct snd_pcm *pcm)
{
	struct snd_pcm_substream *substream;
	int stream;

	for (stream = 0; stream < 2; stream++)
		for (substream = pcm->streams[stream].substream; substream; substream = substream->next)
			snd_pcm_lib_preallocate_free(substream);
	return 0;
}

EXPORT_SYMBOL(snd_pcm_lib_preallocate_free_for_all);

#ifdef CONFIG_SND_VERBOSE_PROCFS
/*
 * read callback for prealloc proc file
 *
 * prints the current allocated size in kB.
 */
static void snd_pcm_lib_preallocate_proc_read(struct snd_info_entry *entry,
					      struct snd_info_buffer *buffer)
{
	struct snd_pcm_substream *substream = entry->private_data;
	snd_iprintf(buffer, "%lu\n", (unsigned long) substream->dma_buffer.bytes / 1024);
}

/*
 * read callback for prealloc_max proc file
 *
 * prints the maximum allowed size in kB.
 */
static void snd_pcm_lib_preallocate_max_proc_read(struct snd_info_entry *entry,
						  struct snd_info_buffer *buffer)
{
	struct snd_pcm_substream *substream = entry->private_data;
	snd_iprintf(buffer, "%lu\n", (unsigned long) substream->dma_max / 1024);
}

/*
 * write callback for prealloc proc file
 *
 * accepts the preallocation size in kB.
 */
static void snd_pcm_lib_preallocate_proc_write(struct snd_info_entry *entry,
					       struct snd_info_buffer *buffer)
{
	struct snd_pcm_substream *substream = entry->private_data;
	char line[64], str[64];
	size_t size;
	struct snd_dma_buffer new_dmab;

	if (substream->runtime) {
		buffer->error = -EBUSY;
		return;
	}
	if (!snd_info_get_line(buffer, line, sizeof(line))) {
		snd_info_get_str(str, line, sizeof(str));
		size = simple_strtoul(str, NULL, 10) * 1024;
		if ((size != 0 && size < 8192) || size > substream->dma_max) {
			buffer->error = -EINVAL;
			return;
		}
		if (substream->dma_buffer.bytes == size)
			return;
		memset(&new_dmab, 0, sizeof(new_dmab));
		new_dmab.dev = substream->dma_buffer.dev;
		if (size > 0) {
			if (snd_dma_alloc_pages(substream->dma_buffer.dev.type,
						substream->dma_buffer.dev.dev,
						size, &new_dmab) < 0) {
				buffer->error = -ENOMEM;
				return;
			}
			substream->buffer_bytes_max = size;
		} else {
			substream->buffer_bytes_max = UINT_MAX;
		}
		if (substream->dma_buffer.area)
			snd_dma_free_pages(&substream->dma_buffer);
		substream->dma_buffer = new_dmab;
	} else {
		buffer->error = -EINVAL;
	}
}

static inline void preallocate_info_init(struct snd_pcm_substream *substream)
{
	struct snd_info_entry *entry;

	if ((entry = snd_info_create_card_entry(substream->pcm->card, "prealloc", substream->proc_root)) != NULL) {
		entry->c.text.read = snd_pcm_lib_preallocate_proc_read;
		entry->c.text.write = snd_pcm_lib_preallocate_proc_write;
		entry->mode |= S_IWUSR;
		entry->private_data = substream;
		if (snd_info_register(entry) < 0) {
			snd_info_free_entry(entry);
			entry = NULL;
		}
	}
	substream->proc_prealloc_entry = entry;
	if ((entry = snd_info_create_card_entry(substream->pcm->card, "prealloc_max", substream->proc_root)) != NULL) {
		entry->c.text.read = snd_pcm_lib_preallocate_max_proc_read;
		entry->private_data = substream;
		if (snd_info_register(entry) < 0) {
			snd_info_free_entry(entry);
			entry = NULL;
		}
	}
	substream->proc_prealloc_max_entry = entry;
}

#else /* !CONFIG_SND_VERBOSE_PROCFS */
#define preallocate_info_init(s)
#endif /* CONFIG_SND_VERBOSE_PROCFS */

/*
 * pre-allocate the buffer and create a proc file for the substream
 */
static int snd_pcm_lib_preallocate_pages1(struct snd_pcm_substream *substream,
					  size_t size, size_t max)
{

	if (size > 0 && preallocate_dma && substream->number < maximum_substreams)
		preallocate_pcm_pages(substream, size);

	if (substream->dma_buffer.bytes > 0)
		substream->buffer_bytes_max = substream->dma_buffer.bytes;
	substream->dma_max = max;
	preallocate_info_init(substream);
	return 0;
}


/**
 * snd_pcm_lib_preallocate_pages - pre-allocation for the given DMA type
 * @substream: the pcm substream instance
 * @type: DMA type (SNDRV_DMA_TYPE_*)
 * @data: DMA type dependant data
 * @size: the requested pre-allocation size in bytes
 * @max: the max. allowed pre-allocation size
 *
 * Do pre-allocation for the given DMA buffer type.
 *
 * When substream->dma_buf_id is set, the function tries to look for
 * the reserved buffer, and the buffer is not freed but reserved at
 * destruction time.  The dma_buf_id must be unique for all systems
 * (in the same DMA buffer type) e.g. using snd_dma_pci_buf_id().
 *
 * Returns zero if successful, or a negative error code on failure.
 */
 /* 预分配页 */
int snd_pcm_lib_preallocate_pages(struct snd_pcm_substream *substream,
				  int type, struct device *data,
				  size_t size, size_t max)
{
	substream->dma_buffer.dev.type = type;
	substream->dma_buffer.dev.dev = data;
	return snd_pcm_lib_preallocate_pages1(substream, size, max);
}

EXPORT_SYMBOL(snd_pcm_lib_preallocate_pages);

/**
 * snd_pcm_lib_preallocate_pages_for_all - pre-allocation for continous memory type (all substreams)
 * @pcm: the pcm instance
 * @type: DMA type (SNDRV_DMA_TYPE_*)
 * @data: DMA type dependant data
 * @size: the requested pre-allocation size in bytes
 * @max: the max. allowed pre-allocation size
 *
 * Do pre-allocation to all substreams of the given pcm for the
 * specified DMA type.
 *
 * Returns zero if successful, or a negative error code on failure.
 */
 /* 分配缓冲区的最简单的方法是调用该函数
     type的取值可查看宏SNDRV_DMA_TYPE_* */
int snd_pcm_lib_preallocate_pages_for_all(struct snd_pcm *pcm,
					  int type, void *data,
					  size_t size, size_t max)
{
	struct snd_pcm_substream *substream;
	int stream, err;

	for (stream = 0; stream < 2; stream++)
		for (substream = pcm->streams[stream].substream; substream; substream = substream->next)
			if ((err = snd_pcm_lib_preallocate_pages(substream, type, data, size, max)) < 0)
				return err;
	return 0;
}

EXPORT_SYMBOL(snd_pcm_lib_preallocate_pages_for_all);

/**
 * snd_pcm_sgbuf_ops_page - get the page struct at the given offset
 * @substream: the pcm substream instance
 * @offset: the buffer offset
 *
 * Returns the page struct at the given buffer offset.
 * Used as the page callback of PCM ops.
 */
 /* 通过给定的偏移量获取页指针 */
struct page *snd_pcm_sgbuf_ops_page(struct snd_pcm_substream *substream, unsigned long offset)
{
	struct snd_sg_buf *sgbuf = snd_pcm_substream_sgbuf(substream);

	unsigned int idx = offset >> PAGE_SHIFT;
	if (idx >= (unsigned int)sgbuf->pages)
		return NULL;
	return sgbuf->page_table[idx];
}

EXPORT_SYMBOL(snd_pcm_sgbuf_ops_page);

/*
 * compute the max chunk size with continuous pages on sg-buffer
 */
 /* 计算SG buffer中最大的块连续页的大小 */
unsigned int snd_pcm_sgbuf_get_chunk_size(struct snd_pcm_substream *substream,
					  unsigned int ofs, unsigned int size)
{
	struct snd_sg_buf *sg = snd_pcm_substream_sgbuf(substream);
	unsigned int start, end, pg;

	start = ofs >> PAGE_SHIFT;
	end = (ofs + size - 1) >> PAGE_SHIFT;
	/* check page continuity */
	pg = sg->table[start].addr >> PAGE_SHIFT;
	for (;;) {
		start++;
		if (start > end)
			break;
		pg++;
		if ((sg->table[start].addr >> PAGE_SHIFT) != pg)
			return (start << PAGE_SHIFT) - ofs;
	}
	/* ok, all on continuous pages */
	return size;
}
EXPORT_SYMBOL(snd_pcm_sgbuf_get_chunk_size);

/**
 * snd_pcm_lib_malloc_pages - allocate the DMA buffer
 * @substream: the substream to allocate the DMA buffer to
 * @size: the requested buffer size in bytes
 *
 * Allocates the DMA buffer on the BUS type given earlier to
 * snd_pcm_lib_preallocate_xxx_pages().
 *
 * Returns 1 if the buffer is changed, 0 if not changed, or a negative
 * code on failure.
 */
 /* 分配DMA缓冲区，仅当DMA缓冲区已预分配的情况下才可调用该函数 */
int snd_pcm_lib_malloc_pages(struct snd_pcm_substream *substream, size_t size)
{
	struct snd_pcm_runtime *runtime;
	struct snd_dma_buffer *dmab = NULL;

	if (PCM_RUNTIME_CHECK(substream))
		return -EINVAL;
	if (snd_BUG_ON(substream->dma_buffer.dev.type ==
		       SNDRV_DMA_TYPE_UNKNOWN))
		return -EINVAL;
	runtime = substream->runtime;

	if (runtime->dma_buffer_p) {
		/* perphaps, we might free the large DMA memory region
		   to save some space here, but the actual solution
		   costs us less time */
		if (runtime->dma_buffer_p->bytes >= size) {
			runtime->dma_bytes = size;
			return 0;	/* ok, do not change */
		}
		snd_pcm_lib_free_pages(substream);
	}
	if (substream->dma_buffer.area != NULL &&
	    substream->dma_buffer.bytes >= size) {
		dmab = &substream->dma_buffer; /* use the pre-allocated buffer */
	} else {
		dmab = kzalloc(sizeof(*dmab), GFP_KERNEL);
		if (! dmab)
			return -ENOMEM;
		dmab->dev = substream->dma_buffer.dev;
		if (snd_dma_alloc_pages(substream->dma_buffer.dev.type,
					substream->dma_buffer.dev.dev,
					size, dmab) < 0) {
			kfree(dmab);
			return -ENOMEM;
		}
	}
	snd_pcm_set_runtime_buffer(substream, dmab);
	runtime->dma_bytes = size;
	return 1;			/* area was changed */
}

EXPORT_SYMBOL(snd_pcm_lib_malloc_pages);

/**
 * snd_pcm_lib_free_pages - release the allocated DMA buffer.
 * @substream: the substream to release the DMA buffer
 *
 * Releases the DMA buffer allocated via snd_pcm_lib_malloc_pages().
 *
 * Returns zero if successful, or a negative error code on failure.
 */
 /* 释放由snd_pcm_lib_malloc_pages函数分配的一致性DMA缓冲区 */
int snd_pcm_lib_free_pages(struct snd_pcm_substream *substream)
{
	struct snd_pcm_runtime *runtime;

	if (PCM_RUNTIME_CHECK(substream))
		return -EINVAL;
	runtime = substream->runtime;
	if (runtime->dma_area == NULL)
		return 0;
	if (runtime->dma_buffer_p != &substream->dma_buffer) {
		/* it's a newly allocated buffer.  release it now. */
		snd_dma_free_pages(runtime->dma_buffer_p);
		kfree(runtime->dma_buffer_p);
	}
	snd_pcm_set_runtime_buffer(substream, NULL);
	return 0;
}

EXPORT_SYMBOL(snd_pcm_lib_free_pages);
