sound/core/pcm_memory.c - third_party/kernel - Git at Google

 // SPDX-License-Identifier: GPL-2.0-or-later
 /*
  *  Digital Audio (PCM) abstract layer
  *  Copyright (c) by Jaroslav Kysela <perex@perex.cz>
  */

 #include <linux/io.h>
 #include <linux/time.h>
 #include <linux/init.h>
 #include <linux/slab.h>
 #include <linux/moduleparam.h>
 #include <linux/vmalloc.h>
 #include <linux/export.h>
 #include <sound/core.h>
 #include <sound/pcm.h>
 #include <sound/info.h>
 #include <sound/initval.h>
 #include "pcm_local.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;

 static unsigned long max_alloc_per_card = 32UL * 1024UL * 1024UL;
 module_param(max_alloc_per_card, ulong, 0644);
 MODULE_PARM_DESC(max_alloc_per_card, "Max total allocation bytes per card.");

 static void __update_allocated_size(struct snd_card *card, ssize_t bytes)
 {
 	card->total_pcm_alloc_bytes += bytes;
 }

 static void update_allocated_size(struct snd_card *card, ssize_t bytes)
 {
 	mutex_lock(&card->memory_mutex);
 	__update_allocated_size(card, bytes);
 	mutex_unlock(&card->memory_mutex);
 }

 static void decrease_allocated_size(struct snd_card *card, size_t bytes)
 {
 	mutex_lock(&card->memory_mutex);
 	WARN_ON(card->total_pcm_alloc_bytes < bytes);
 	__update_allocated_size(card, -(ssize_t)bytes);
 	mutex_unlock(&card->memory_mutex);
 }

 static int do_alloc_pages(struct snd_card *card, int type, struct device *dev,
 			  size_t size, struct snd_dma_buffer *dmab)
 {
 	int err;

 	/* check and reserve the requested size */
 	mutex_lock(&card->memory_mutex);
 	if (max_alloc_per_card &&
 	    card->total_pcm_alloc_bytes + size > max_alloc_per_card) {
 		mutex_unlock(&card->memory_mutex);
 		return -ENOMEM;
 	}
 	__update_allocated_size(card, size);
 	mutex_unlock(&card->memory_mutex);

 	err = snd_dma_alloc_pages(type, dev, size, dmab);
 	if (!err) {
 		/* the actual allocation size might be bigger than requested,
 		 * and we need to correct the account
 		 */
 		if (dmab->bytes != size)
 			update_allocated_size(card, dmab->bytes - size);
 	} else {
 		/* take back on allocation failure */
 		decrease_allocated_size(card, size);
 	}
 	return err;
 }

 static void do_free_pages(struct snd_card *card, struct snd_dma_buffer *dmab)
 {
 	if (!dmab->area)
 		return;
 	decrease_allocated_size(card, dmab->bytes);
 	snd_dma_free_pages(dmab);
 	dmab->area = NULL;
 }

 /*
  * 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, bool no_fallback)
 {
 	struct snd_dma_buffer *dmab = &substream->dma_buffer;
 	struct snd_card *card = substream->pcm->card;
 	size_t orig_size = size;
 	int err;

 	do {
 		err = do_alloc_pages(card, dmab->dev.type, dmab->dev.dev,
 				     size, dmab);
 		if (err != -ENOMEM)
 			return err;
 		if (no_fallback)
 			break;
 		size >>= 1;
 	} while (size >= snd_minimum_buffer);
 	dmab->bytes = 0; /* tell error */
 	pr_warn("ALSA pcmC%dD%d%c,%d:%s: cannot preallocate for size %zu\n",
 		substream->pcm->card->number, substream->pcm->device,
 		substream->stream ? 'c' : 'p', substream->number,
 		substream->pcm->name, orig_size);
 	return -ENOMEM;
 }

 /**
  * 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.
  */
 void snd_pcm_lib_preallocate_free(struct snd_pcm_substream *substream)
 {
 	do_free_pages(substream->pcm->card, &substream->dma_buffer);
 }

 /**
  * 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.
  */
 void snd_pcm_lib_preallocate_free_for_all(struct snd_pcm *pcm)
 {
 	struct snd_pcm_substream *substream;
 	int stream;

 	for_each_pcm_substream(pcm, stream, substream)
 		snd_pcm_lib_preallocate_free(substream);
 }
 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;
 	struct snd_card *card = substream->pcm->card;
 	char line[64], str[64];
 	size_t size;
 	struct snd_dma_buffer new_dmab;

 	mutex_lock(&substream->pcm->open_mutex);
 	if (substream->runtime) {
 		buffer->error = -EBUSY;
 		goto unlock;
 	}
 	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;
 			goto unlock;
 		}
 		if (substream->dma_buffer.bytes == size)
 			goto unlock;
 		memset(&new_dmab, 0, sizeof(new_dmab));
 		new_dmab.dev = substream->dma_buffer.dev;
 		if (size > 0) {
 			if (do_alloc_pages(card,
 					   substream->dma_buffer.dev.type,
 					   substream->dma_buffer.dev.dev,
 					   size, &new_dmab) < 0) {
 				buffer->error = -ENOMEM;
 				pr_debug("ALSA pcmC%dD%d%c,%d:%s: cannot preallocate for size %zu\n",
 					 substream->pcm->card->number, substream->pcm->device,
 					 substream->stream ? 'c' : 'p', substream->number,
 					 substream->pcm->name, size);
 				goto unlock;
 			}
 			substream->buffer_bytes_max = size;
 		} else {
 			substream->buffer_bytes_max = UINT_MAX;
 		}
 		if (substream->dma_buffer.area)
 			do_free_pages(card, &substream->dma_buffer);
 		substream->dma_buffer = new_dmab;
 	} else {
 		buffer->error = -EINVAL;
 	}
  unlock:
 	mutex_unlock(&substream->pcm->open_mutex);
 }

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

 	entry = snd_info_create_card_entry(substream->pcm->card, "prealloc",
 					   substream->proc_root);
 	if (entry) {
 		snd_info_set_text_ops(entry, substream,
 				      snd_pcm_lib_preallocate_proc_read);
 		entry->c.text.write = snd_pcm_lib_preallocate_proc_write;
 		entry->mode |= 0200;
 	}
 	entry = snd_info_create_card_entry(substream->pcm->card, "prealloc_max",
 					   substream->proc_root);
 	if (entry)
 		snd_info_set_text_ops(entry, substream,
 				      snd_pcm_lib_preallocate_max_proc_read);
 }

 #else /* !CONFIG_SND_VERBOSE_PROCFS */
 static inline void preallocate_info_init(struct snd_pcm_substream *substream)
 {
 }
 #endif /* CONFIG_SND_VERBOSE_PROCFS */

 /*
  * pre-allocate the buffer and create a proc file for the substream
  */
 static int preallocate_pages(struct snd_pcm_substream *substream,
 			      int type, struct device *data,
 			      size_t size, size_t max, bool managed)
 {
 	int err;

 	if (snd_BUG_ON(substream->dma_buffer.dev.type))
 		return -EINVAL;

 	substream->dma_buffer.dev.type = type;
 	substream->dma_buffer.dev.dev = data;

 	if (size > 0) {
 		if (!max) {
 			/* no fallback, only also inform -ENOMEM */
 			err = preallocate_pcm_pages(substream, size, true);
 			if (err < 0)
 				return err;
 		} else if (preallocate_dma &&
 			   substream->number < maximum_substreams) {
 			err = preallocate_pcm_pages(substream, size, false);
 			if (err < 0 && err != -ENOMEM)
 				return err;
 		}
 	}

 	if (substream->dma_buffer.bytes > 0)
 		substream->buffer_bytes_max = substream->dma_buffer.bytes;
 	substream->dma_max = max;
 	if (max > 0)
 		preallocate_info_init(substream);
 	if (managed)
 		substream->managed_buffer_alloc = 1;
 	return 0;
 }

 static int preallocate_pages_for_all(struct snd_pcm *pcm, int type,
 				      void *data, size_t size, size_t max,
 				      bool managed)
 {
 	struct snd_pcm_substream *substream;
 	int stream, err;

 	for_each_pcm_substream(pcm, stream, substream) {
 		err = preallocate_pages(substream, type, data, size, max, managed);
 		if (err < 0)
 			return err;
 	}
 	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 dependent 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.
  */
 void snd_pcm_lib_preallocate_pages(struct snd_pcm_substream *substream,
 				  int type, struct device *data,
 				  size_t size, size_t max)
 {
 	preallocate_pages(substream, type, data, size, max, false);
 }
 EXPORT_SYMBOL(snd_pcm_lib_preallocate_pages);

 /**
  * snd_pcm_lib_preallocate_pages_for_all - pre-allocation for continuous memory type (all substreams)
  * @pcm: the pcm instance
  * @type: DMA type (SNDRV_DMA_TYPE_*)
  * @data: DMA type dependent 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.
  */
 void snd_pcm_lib_preallocate_pages_for_all(struct snd_pcm *pcm,
 					  int type, void *data,
 					  size_t size, size_t max)
 {
 	preallocate_pages_for_all(pcm, type, data, size, max, false);
 }
 EXPORT_SYMBOL(snd_pcm_lib_preallocate_pages_for_all);

 /**
  * snd_pcm_set_managed_buffer - set up buffer management for a substream
  * @substream: the pcm substream instance
  * @type: DMA type (SNDRV_DMA_TYPE_*)
  * @data: DMA type dependent 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, and set the managed
  * buffer allocation mode to the given substream.
  * In this mode, PCM core will allocate a buffer automatically before PCM
  * hw_params ops call, and release the buffer after PCM hw_free ops call
  * as well, so that the driver doesn't need to invoke the allocation and
  * the release explicitly in its callback.
  * When a buffer is actually allocated before the PCM hw_params call, it
  * turns on the runtime buffer_changed flag for drivers changing their h/w
  * parameters accordingly.
  *
  * When @size is non-zero and @max is zero, this tries to allocate for only
  * the exact buffer size without fallback, and may return -ENOMEM.
  * Otherwise, the function tries to allocate smaller chunks if the allocation
  * fails.  This is the behavior of snd_pcm_set_fixed_buffer().
  *
  * When both @size and @max are zero, the function only sets up the buffer
  * for later dynamic allocations. It's used typically for buffers with
  * SNDRV_DMA_TYPE_VMALLOC type.
  *
  * Upon successful buffer allocation and setup, the function returns 0.
  */
 int snd_pcm_set_managed_buffer(struct snd_pcm_substream *substream, int type,
 				struct device *data, size_t size, size_t max)
 {
 	return preallocate_pages(substream, type, data, size, max, true);
 }
 EXPORT_SYMBOL(snd_pcm_set_managed_buffer);

 /**
  * snd_pcm_set_managed_buffer_all - set up buffer management for all substreams
  *	for all substreams
  * @pcm: the pcm instance
  * @type: DMA type (SNDRV_DMA_TYPE_*)
  * @data: DMA type dependent 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 and size, and set the managed_buffer_alloc flag to each substream.
  */
 int snd_pcm_set_managed_buffer_all(struct snd_pcm *pcm, int type,
 				   struct device *data,
 				   size_t size, size_t max)
 {
 	return preallocate_pages_for_all(pcm, type, data, size, max, true);
 }
 EXPORT_SYMBOL(snd_pcm_set_managed_buffer_all);

 /**
  * 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().
  *
  * Return: 1 if the buffer is changed, 0 if not changed, or a negative
  * code on failure.
  */
 int snd_pcm_lib_malloc_pages(struct snd_pcm_substream *substream, size_t size)
 {
 	struct snd_card *card;
 	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;
 	card = substream->pcm->card;

 	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 {
 		/* dma_max=0 means the fixed size preallocation */
 		if (substream->dma_buffer.area && !substream->dma_max)
 			return -ENOMEM;
 		dmab = kzalloc(sizeof(*dmab), GFP_KERNEL);
 		if (! dmab)
 			return -ENOMEM;
 		dmab->dev = substream->dma_buffer.dev;
 		if (do_alloc_pages(card,
 				   substream->dma_buffer.dev.type,
 				   substream->dma_buffer.dev.dev,
 				   size, dmab) < 0) {
 			kfree(dmab);
 			pr_debug("ALSA pcmC%dD%d%c,%d:%s: cannot preallocate for size %zu\n",
 				 substream->pcm->card->number, substream->pcm->device,
 				 substream->stream ? 'c' : 'p', substream->number,
 				 substream->pcm->name, size);
 			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().
  *
  * Return: Zero if successful, or a negative error code on failure.
  */
 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) {
 		struct snd_card *card = substream->pcm->card;

 		/* it's a newly allocated buffer.  release it now. */
 		do_free_pages(card, 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);

 int _snd_pcm_lib_alloc_vmalloc_buffer(struct snd_pcm_substream *substream,
 				      size_t size, gfp_t gfp_flags)
 {
 	struct snd_pcm_runtime *runtime;

 	if (PCM_RUNTIME_CHECK(substream))
 		return -EINVAL;
 	runtime = substream->runtime;
 	if (runtime->dma_area) {
 		if (runtime->dma_bytes >= size)
 			return 0; /* already large enough */
 		vfree(runtime->dma_area);
 	}
 	runtime->dma_area = __vmalloc(size, gfp_flags);
 	if (!runtime->dma_area)
 		return -ENOMEM;
 	runtime->dma_bytes = size;
 	return 1;
 }
 EXPORT_SYMBOL(_snd_pcm_lib_alloc_vmalloc_buffer);

 /**
  * snd_pcm_lib_free_vmalloc_buffer - free vmalloc buffer
  * @substream: the substream with a buffer allocated by
  *	snd_pcm_lib_alloc_vmalloc_buffer()
  *
  * Return: Zero if successful, or a negative error code on failure.
  */
 int snd_pcm_lib_free_vmalloc_buffer(struct snd_pcm_substream *substream)
 {
 	struct snd_pcm_runtime *runtime;

 	if (PCM_RUNTIME_CHECK(substream))
 		return -EINVAL;
 	runtime = substream->runtime;
 	vfree(runtime->dma_area);
 	runtime->dma_area = NULL;
 	return 0;
 }
 EXPORT_SYMBOL(snd_pcm_lib_free_vmalloc_buffer);

 /**
  * snd_pcm_lib_get_vmalloc_page - map vmalloc buffer offset to page struct
  * @substream: the substream with a buffer allocated by
  *	snd_pcm_lib_alloc_vmalloc_buffer()
  * @offset: offset in the buffer
  *
  * This function is to be used as the page callback in the PCM ops.
  *
  * Return: The page struct, or %NULL on failure.
  */
 struct page *snd_pcm_lib_get_vmalloc_page(struct snd_pcm_substream *substream,
 					  unsigned long offset)
 {
 	return vmalloc_to_page(substream->runtime->dma_area + offset);
 }
 EXPORT_SYMBOL(snd_pcm_lib_get_vmalloc_page);
	// SPDX-License-Identifier: GPL-2.0-or-later
	/*
	* Digital Audio (PCM) abstract layer
	* Copyright (c) by Jaroslav Kysela <perex@perex.cz>
	*/

	#include <linux/io.h>
	#include <linux/time.h>
	#include <linux/init.h>
	#include <linux/slab.h>
	#include <linux/moduleparam.h>
	#include <linux/vmalloc.h>
	#include <linux/export.h>
	#include <sound/core.h>
	#include <sound/pcm.h>
	#include <sound/info.h>
	#include <sound/initval.h>
	#include "pcm_local.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;

	static unsigned long max_alloc_per_card = 32UL * 1024UL * 1024UL;
	module_param(max_alloc_per_card, ulong, 0644);
	MODULE_PARM_DESC(max_alloc_per_card, "Max total allocation bytes per card.");

	static void __update_allocated_size(struct snd_card *card, ssize_t bytes)
	{
	card->total_pcm_alloc_bytes += bytes;
	}

	static void update_allocated_size(struct snd_card *card, ssize_t bytes)
	{
	mutex_lock(&card->memory_mutex);
	__update_allocated_size(card, bytes);
	mutex_unlock(&card->memory_mutex);
	}

	static void decrease_allocated_size(struct snd_card *card, size_t bytes)
	{
	mutex_lock(&card->memory_mutex);
	WARN_ON(card->total_pcm_alloc_bytes < bytes);
	__update_allocated_size(card, -(ssize_t)bytes);
	mutex_unlock(&card->memory_mutex);
	}

	static int do_alloc_pages(struct snd_card card, int type, struct device dev,
	size_t size, struct snd_dma_buffer *dmab)
	{
	int err;

	/* check and reserve the requested size */
	mutex_lock(&card->memory_mutex);
	if (max_alloc_per_card &&
	card->total_pcm_alloc_bytes + size > max_alloc_per_card) {
	mutex_unlock(&card->memory_mutex);
	return -ENOMEM;
	}
	__update_allocated_size(card, size);
	mutex_unlock(&card->memory_mutex);

	err = snd_dma_alloc_pages(type, dev, size, dmab);
	if (!err) {
	/* the actual allocation size might be bigger than requested,
	* and we need to correct the account
	*/
	if (dmab->bytes != size)
	update_allocated_size(card, dmab->bytes - size);
	} else {
	/* take back on allocation failure */
	decrease_allocated_size(card, size);
	}
	return err;
	}

	static void do_free_pages(struct snd_card card, struct snd_dma_buffer dmab)
	{
	if (!dmab->area)
	return;
	decrease_allocated_size(card, dmab->bytes);
	snd_dma_free_pages(dmab);
	dmab->area = NULL;
	}

	/*
	* 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, bool no_fallback)
	{
	struct snd_dma_buffer *dmab = &substream->dma_buffer;
	struct snd_card *card = substream->pcm->card;
	size_t orig_size = size;
	int err;

	do {
	err = do_alloc_pages(card, dmab->dev.type, dmab->dev.dev,
	size, dmab);
	if (err != -ENOMEM)
	return err;
	if (no_fallback)
	break;
	size >>= 1;
	} while (size >= snd_minimum_buffer);
	dmab->bytes = 0; /* tell error */
	pr_warn("ALSA pcmC%dD%d%c,%d:%s: cannot preallocate for size %zu\n",
	substream->pcm->card->number, substream->pcm->device,
	substream->stream ? 'c' : 'p', substream->number,
	substream->pcm->name, orig_size);
	return -ENOMEM;
	}

	/**
	* 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.
	*/
	void snd_pcm_lib_preallocate_free(struct snd_pcm_substream *substream)
	{
	do_free_pages(substream->pcm->card, &substream->dma_buffer);
	}

	/**
	* 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.
	*/
	void snd_pcm_lib_preallocate_free_for_all(struct snd_pcm *pcm)
	{
	struct snd_pcm_substream *substream;
	int stream;

	for_each_pcm_substream(pcm, stream, substream)
	snd_pcm_lib_preallocate_free(substream);
	}
	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;
	struct snd_card *card = substream->pcm->card;
	char line[64], str[64];
	size_t size;
	struct snd_dma_buffer new_dmab;

	mutex_lock(&substream->pcm->open_mutex);
	if (substream->runtime) {
	buffer->error = -EBUSY;
	goto unlock;
	}
	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;
	goto unlock;
	}
	if (substream->dma_buffer.bytes == size)
	goto unlock;
	memset(&new_dmab, 0, sizeof(new_dmab));
	new_dmab.dev = substream->dma_buffer.dev;
	if (size > 0) {
	if (do_alloc_pages(card,
	substream->dma_buffer.dev.type,
	substream->dma_buffer.dev.dev,
	size, &new_dmab) < 0) {
	buffer->error = -ENOMEM;
	pr_debug("ALSA pcmC%dD%d%c,%d:%s: cannot preallocate for size %zu\n",
	substream->pcm->card->number, substream->pcm->device,
	substream->stream ? 'c' : 'p', substream->number,
	substream->pcm->name, size);
	goto unlock;
	}
	substream->buffer_bytes_max = size;
	} else {
	substream->buffer_bytes_max = UINT_MAX;
	}
	if (substream->dma_buffer.area)
	do_free_pages(card, &substream->dma_buffer);
	substream->dma_buffer = new_dmab;
	} else {
	buffer->error = -EINVAL;
	}
	unlock:
	mutex_unlock(&substream->pcm->open_mutex);
	}

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

	entry = snd_info_create_card_entry(substream->pcm->card, "prealloc",
	substream->proc_root);
	if (entry) {
	snd_info_set_text_ops(entry, substream,
	snd_pcm_lib_preallocate_proc_read);
	entry->c.text.write = snd_pcm_lib_preallocate_proc_write;
	entry->mode \|= 0200;
	}
	entry = snd_info_create_card_entry(substream->pcm->card, "prealloc_max",
	substream->proc_root);
	if (entry)
	snd_info_set_text_ops(entry, substream,
	snd_pcm_lib_preallocate_max_proc_read);
	}

	#else /* !CONFIG_SND_VERBOSE_PROCFS */
	static inline void preallocate_info_init(struct snd_pcm_substream *substream)
	{
	}
	#endif /* CONFIG_SND_VERBOSE_PROCFS */

	/*
	* pre-allocate the buffer and create a proc file for the substream
	*/
	static int preallocate_pages(struct snd_pcm_substream *substream,
	int type, struct device *data,
	size_t size, size_t max, bool managed)
	{
	int err;

	if (snd_BUG_ON(substream->dma_buffer.dev.type))
	return -EINVAL;

	substream->dma_buffer.dev.type = type;
	substream->dma_buffer.dev.dev = data;

	if (size > 0) {
	if (!max) {
	/* no fallback, only also inform -ENOMEM */
	err = preallocate_pcm_pages(substream, size, true);
	if (err < 0)
	return err;
	} else if (preallocate_dma &&
	substream->number < maximum_substreams) {
	err = preallocate_pcm_pages(substream, size, false);
	if (err < 0 && err != -ENOMEM)
	return err;
	}
	}

	if (substream->dma_buffer.bytes > 0)
	substream->buffer_bytes_max = substream->dma_buffer.bytes;
	substream->dma_max = max;
	if (max > 0)
	preallocate_info_init(substream);
	if (managed)
	substream->managed_buffer_alloc = 1;
	return 0;
	}

	static int preallocate_pages_for_all(struct snd_pcm *pcm, int type,
	void *data, size_t size, size_t max,
	bool managed)
	{
	struct snd_pcm_substream *substream;
	int stream, err;

	for_each_pcm_substream(pcm, stream, substream) {
	err = preallocate_pages(substream, type, data, size, max, managed);
	if (err < 0)
	return err;
	}
	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 dependent 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.
	*/
	void snd_pcm_lib_preallocate_pages(struct snd_pcm_substream *substream,
	int type, struct device *data,
	size_t size, size_t max)
	{
	preallocate_pages(substream, type, data, size, max, false);
	}
	EXPORT_SYMBOL(snd_pcm_lib_preallocate_pages);

	/**
	* snd_pcm_lib_preallocate_pages_for_all - pre-allocation for continuous memory type (all substreams)
	* @pcm: the pcm instance
	* @type: DMA type (SNDRV_DMA_TYPE_*)
	* @data: DMA type dependent 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.
	*/
	void snd_pcm_lib_preallocate_pages_for_all(struct snd_pcm *pcm,
	int type, void *data,
	size_t size, size_t max)
	{
	preallocate_pages_for_all(pcm, type, data, size, max, false);
	}
	EXPORT_SYMBOL(snd_pcm_lib_preallocate_pages_for_all);

	/**
	* snd_pcm_set_managed_buffer - set up buffer management for a substream
	* @substream: the pcm substream instance
	* @type: DMA type (SNDRV_DMA_TYPE_*)
	* @data: DMA type dependent 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, and set the managed
	* buffer allocation mode to the given substream.
	* In this mode, PCM core will allocate a buffer automatically before PCM
	* hw_params ops call, and release the buffer after PCM hw_free ops call
	* as well, so that the driver doesn't need to invoke the allocation and
	* the release explicitly in its callback.
	* When a buffer is actually allocated before the PCM hw_params call, it
	* turns on the runtime buffer_changed flag for drivers changing their h/w
	* parameters accordingly.
	*
	* When @size is non-zero and @max is zero, this tries to allocate for only
	* the exact buffer size without fallback, and may return -ENOMEM.
	* Otherwise, the function tries to allocate smaller chunks if the allocation
	* fails. This is the behavior of snd_pcm_set_fixed_buffer().
	*
	* When both @size and @max are zero, the function only sets up the buffer
	* for later dynamic allocations. It's used typically for buffers with
	* SNDRV_DMA_TYPE_VMALLOC type.
	*
	* Upon successful buffer allocation and setup, the function returns 0.
	*/
	int snd_pcm_set_managed_buffer(struct snd_pcm_substream *substream, int type,
	struct device *data, size_t size, size_t max)
	{
	return preallocate_pages(substream, type, data, size, max, true);
	}
	EXPORT_SYMBOL(snd_pcm_set_managed_buffer);

	/**
	* snd_pcm_set_managed_buffer_all - set up buffer management for all substreams
	* for all substreams
	* @pcm: the pcm instance
	* @type: DMA type (SNDRV_DMA_TYPE_*)
	* @data: DMA type dependent 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 and size, and set the managed_buffer_alloc flag to each substream.
	*/
	int snd_pcm_set_managed_buffer_all(struct snd_pcm *pcm, int type,
	struct device *data,
	size_t size, size_t max)
	{
	return preallocate_pages_for_all(pcm, type, data, size, max, true);
	}
	EXPORT_SYMBOL(snd_pcm_set_managed_buffer_all);

	/**
	* 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().
	*
	* Return: 1 if the buffer is changed, 0 if not changed, or a negative
	* code on failure.
	*/
	int snd_pcm_lib_malloc_pages(struct snd_pcm_substream *substream, size_t size)
	{
	struct snd_card *card;
	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;
	card = substream->pcm->card;

	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 {
	/* dma_max=0 means the fixed size preallocation */
	if (substream->dma_buffer.area && !substream->dma_max)
	return -ENOMEM;
	dmab = kzalloc(sizeof(*dmab), GFP_KERNEL);
	if (! dmab)
	return -ENOMEM;
	dmab->dev = substream->dma_buffer.dev;
	if (do_alloc_pages(card,
	substream->dma_buffer.dev.type,
	substream->dma_buffer.dev.dev,
	size, dmab) < 0) {
	kfree(dmab);
	pr_debug("ALSA pcmC%dD%d%c,%d:%s: cannot preallocate for size %zu\n",
	substream->pcm->card->number, substream->pcm->device,
	substream->stream ? 'c' : 'p', substream->number,
	substream->pcm->name, size);
	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().
	*
	* Return: Zero if successful, or a negative error code on failure.
	*/
	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) {
	struct snd_card *card = substream->pcm->card;

	/* it's a newly allocated buffer. release it now. */
	do_free_pages(card, 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);

	int _snd_pcm_lib_alloc_vmalloc_buffer(struct snd_pcm_substream *substream,
	size_t size, gfp_t gfp_flags)
	{
	struct snd_pcm_runtime *runtime;

	if (PCM_RUNTIME_CHECK(substream))
	return -EINVAL;
	runtime = substream->runtime;
	if (runtime->dma_area) {
	if (runtime->dma_bytes >= size)
	return 0; /* already large enough */
	vfree(runtime->dma_area);
	}
	runtime->dma_area = __vmalloc(size, gfp_flags);
	if (!runtime->dma_area)
	return -ENOMEM;
	runtime->dma_bytes = size;
	return 1;
	}
	EXPORT_SYMBOL(_snd_pcm_lib_alloc_vmalloc_buffer);

	/**
	* snd_pcm_lib_free_vmalloc_buffer - free vmalloc buffer
	* @substream: the substream with a buffer allocated by
	* snd_pcm_lib_alloc_vmalloc_buffer()
	*
	* Return: Zero if successful, or a negative error code on failure.
	*/
	int snd_pcm_lib_free_vmalloc_buffer(struct snd_pcm_substream *substream)
	{
	struct snd_pcm_runtime *runtime;

	if (PCM_RUNTIME_CHECK(substream))
	return -EINVAL;
	runtime = substream->runtime;
	vfree(runtime->dma_area);
	runtime->dma_area = NULL;
	return 0;
	}
	EXPORT_SYMBOL(snd_pcm_lib_free_vmalloc_buffer);

	/**
	* snd_pcm_lib_get_vmalloc_page - map vmalloc buffer offset to page struct
	* @substream: the substream with a buffer allocated by
	* snd_pcm_lib_alloc_vmalloc_buffer()
	* @offset: offset in the buffer
	*
	* This function is to be used as the page callback in the PCM ops.
	*
	* Return: The page struct, or %NULL on failure.
	*/
	struct page snd_pcm_lib_get_vmalloc_page(struct snd_pcm_substream substream,
	unsigned long offset)
	{
	return vmalloc_to_page(substream->runtime->dma_area + offset);
	}
	EXPORT_SYMBOL(snd_pcm_lib_get_vmalloc_page);