mm/dmapool.c - SHIFTPHONES/android_kernel_shift_sdm845 - Gitiles

 /*
  * DMA Pool allocator
  *
  * Copyright 2001 David Brownell
  * Copyright 2007 Intel Corporation
  *   Author: Matthew Wilcox <willy@linux.intel.com>
  *
  * This software may be redistributed and/or modified under the terms of
  * the GNU General Public License ("GPL") version 2 as published by the
  * Free Software Foundation.
  *
  * This allocator returns small blocks of a given size which are DMA-able by
  * the given device.  It uses the dma_alloc_coherent page allocator to get
  * new pages, then splits them up into blocks of the required size.
  * Many older drivers still have their own code to do this.
  *
  * The current design of this allocator is fairly simple.  The pool is
  * represented by the 'struct dma_pool' which keeps a doubly-linked list of
  * allocated pages.  Each page in the page_list is split into blocks of at
  * least 'size' bytes.
  */

 #include <linux/device.h>
 #include <linux/dma-mapping.h>
 #include <linux/dmapool.h>
 #include <linux/kernel.h>
 #include <linux/list.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
 #include <linux/poison.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/spinlock.h>
 #include <linux/string.h>
 #include <linux/types.h>
 #include <linux/wait.h>

 struct dma_pool {		/* the pool */
 	struct list_head page_list;
 	spinlock_t lock;
 	size_t blocks_per_page;
 	size_t size;
 	struct device *dev;
 	size_t allocation;
 	char name[32];
 	wait_queue_head_t waitq;
 	struct list_head pools;
 };

 struct dma_page {		/* cacheable header for 'allocation' bytes */
 	struct list_head page_list;
 	void *vaddr;
 	dma_addr_t dma;
 	unsigned in_use;
 	unsigned long bitmap[0];
 };

 #define	POOL_TIMEOUT_JIFFIES	((100 /* msec */ * HZ) / 1000)

 static DEFINE_MUTEX(pools_lock);

 static ssize_t
 show_pools(struct device *dev, struct device_attribute *attr, char *buf)
 {
 	unsigned temp;
 	unsigned size;
 	char *next;
 	struct dma_page *page;
 	struct dma_pool *pool;

 	next = buf;
 	size = PAGE_SIZE;

 	temp = scnprintf(next, size, "poolinfo - 0.1\n");
 	size -= temp;
 	next += temp;

 	mutex_lock(&pools_lock);
 	list_for_each_entry(pool, &dev->dma_pools, pools) {
 		unsigned pages = 0;
 		unsigned blocks = 0;

 		list_for_each_entry(page, &pool->page_list, page_list) {
 			pages++;
 			blocks += page->in_use;
 		}

 		/* per-pool info, no real statistics yet */
 		temp = scnprintf(next, size, "%-16s %4u %4Zu %4Zu %2u\n",
 				 pool->name,
 				 blocks, pages * pool->blocks_per_page,
 				 pool->size, pages);
 		size -= temp;
 		next += temp;
 	}
 	mutex_unlock(&pools_lock);

 	return PAGE_SIZE - size;
 }

 static DEVICE_ATTR(pools, S_IRUGO, show_pools, NULL);

 /**
  * dma_pool_create - Creates a pool of consistent memory blocks, for dma.
  * @name: name of pool, for diagnostics
  * @dev: device that will be doing the DMA
  * @size: size of the blocks in this pool.
  * @align: alignment requirement for blocks; must be a power of two
  * @allocation: returned blocks won't cross this boundary (or zero)
  * Context: !in_interrupt()
  *
  * Returns a dma allocation pool with the requested characteristics, or
  * null if one can't be created.  Given one of these pools, dma_pool_alloc()
  * may be used to allocate memory.  Such memory will all have "consistent"
  * DMA mappings, accessible by the device and its driver without using
  * cache flushing primitives.  The actual size of blocks allocated may be
  * larger than requested because of alignment.
  *
  * If allocation is nonzero, objects returned from dma_pool_alloc() won't
  * cross that size boundary.  This is useful for devices which have
  * addressing restrictions on individual DMA transfers, such as not crossing
  * boundaries of 4KBytes.
  */
 struct dma_pool *dma_pool_create(const char *name, struct device *dev,
 				 size_t size, size_t align, size_t allocation)
 {
 	struct dma_pool *retval;

 	if (align == 0) {
 		align = 1;
 	} else if (align & (align - 1)) {
 		return NULL;
 	}

 	if (size == 0)
 		return NULL;

 	if ((size % align) != 0)
 		size = ALIGN(size, align);

 	if (allocation == 0) {
 		if (PAGE_SIZE < size)
 			allocation = size;
 		else
 			allocation = PAGE_SIZE;
 		/* FIXME: round up for less fragmentation */
 	} else if (allocation < size)
 		return NULL;

 	if (!
 	    (retval =
 	     kmalloc_node(sizeof *retval, GFP_KERNEL, dev_to_node(dev))))
 		return retval;

 	strlcpy(retval->name, name, sizeof retval->name);

 	retval->dev = dev;

 	INIT_LIST_HEAD(&retval->page_list);
 	spin_lock_init(&retval->lock);
 	retval->size = size;
 	retval->allocation = allocation;
 	retval->blocks_per_page = allocation / size;
 	init_waitqueue_head(&retval->waitq);

 	if (dev) {
 		int ret;

 		mutex_lock(&pools_lock);
 		if (list_empty(&dev->dma_pools))
 			ret = device_create_file(dev, &dev_attr_pools);
 		else
 			ret = 0;
 		/* note:  not currently insisting "name" be unique */
 		if (!ret)
 			list_add(&retval->pools, &dev->dma_pools);
 		else {
 			kfree(retval);
 			retval = NULL;
 		}
 		mutex_unlock(&pools_lock);
 	} else
 		INIT_LIST_HEAD(&retval->pools);

 	return retval;
 }
 EXPORT_SYMBOL(dma_pool_create);

 static struct dma_page *pool_alloc_page(struct dma_pool *pool, gfp_t mem_flags)
 {
 	struct dma_page *page;
 	int mapsize;

 	mapsize = pool->blocks_per_page;
 	mapsize = (mapsize + BITS_PER_LONG - 1) / BITS_PER_LONG;
 	mapsize *= sizeof(long);

 	page = kmalloc(mapsize + sizeof *page, mem_flags);
 	if (!page)
 		return NULL;
 	page->vaddr = dma_alloc_coherent(pool->dev,
 					 pool->allocation,
 					 &page->dma, mem_flags);
 	if (page->vaddr) {
 		memset(page->bitmap, 0xff, mapsize);	/* bit set == free */
 #ifdef	CONFIG_DEBUG_SLAB
 		memset(page->vaddr, POOL_POISON_FREED, pool->allocation);
 #endif
 		list_add(&page->page_list, &pool->page_list);
 		page->in_use = 0;
 	} else {
 		kfree(page);
 		page = NULL;
 	}
 	return page;
 }

 static inline int is_page_busy(int blocks, unsigned long *bitmap)
 {
 	while (blocks > 0) {
 		if (*bitmap++ != ~0UL)
 			return 1;
 		blocks -= BITS_PER_LONG;
 	}
 	return 0;
 }

 static void pool_free_page(struct dma_pool *pool, struct dma_page *page)
 {
 	dma_addr_t dma = page->dma;

 #ifdef	CONFIG_DEBUG_SLAB
 	memset(page->vaddr, POOL_POISON_FREED, pool->allocation);
 #endif
 	dma_free_coherent(pool->dev, pool->allocation, page->vaddr, dma);
 	list_del(&page->page_list);
 	kfree(page);
 }

 /**
  * dma_pool_destroy - destroys a pool of dma memory blocks.
  * @pool: dma pool that will be destroyed
  * Context: !in_interrupt()
  *
  * Caller guarantees that no more memory from the pool is in use,
  * and that nothing will try to use the pool after this call.
  */
 void dma_pool_destroy(struct dma_pool *pool)
 {
 	mutex_lock(&pools_lock);
 	list_del(&pool->pools);
 	if (pool->dev && list_empty(&pool->dev->dma_pools))
 		device_remove_file(pool->dev, &dev_attr_pools);
 	mutex_unlock(&pools_lock);

 	while (!list_empty(&pool->page_list)) {
 		struct dma_page *page;
 		page = list_entry(pool->page_list.next,
 				  struct dma_page, page_list);
 		if (is_page_busy(pool->blocks_per_page, page->bitmap)) {
 			if (pool->dev)
 				dev_err(pool->dev,
 					"dma_pool_destroy %s, %p busy\n",
 					pool->name, page->vaddr);
 			else
 				printk(KERN_ERR
 				       "dma_pool_destroy %s, %p busy\n",
 				       pool->name, page->vaddr);
 			/* leak the still-in-use consistent memory */
 			list_del(&page->page_list);
 			kfree(page);
 		} else
 			pool_free_page(pool, page);
 	}

 	kfree(pool);
 }
 EXPORT_SYMBOL(dma_pool_destroy);

 /**
  * dma_pool_alloc - get a block of consistent memory
  * @pool: dma pool that will produce the block
  * @mem_flags: GFP_* bitmask
  * @handle: pointer to dma address of block
  *
  * This returns the kernel virtual address of a currently unused block,
  * and reports its dma address through the handle.
  * If such a memory block can't be allocated, %NULL is returned.
  */
 void *dma_pool_alloc(struct dma_pool *pool, gfp_t mem_flags,
 		     dma_addr_t *handle)
 {
 	unsigned long flags;
 	struct dma_page *page;
 	int map, block;
 	size_t offset;
 	void *retval;

 	spin_lock_irqsave(&pool->lock, flags);
  restart:
 	list_for_each_entry(page, &pool->page_list, page_list) {
 		int i;
 		/* only cachable accesses here ... */
 		for (map = 0, i = 0;
 		     i < pool->blocks_per_page; i += BITS_PER_LONG, map++) {
 			if (page->bitmap[map] == 0)
 				continue;
 			block = ffz(~page->bitmap[map]);
 			if ((i + block) < pool->blocks_per_page) {
 				clear_bit(block, &page->bitmap[map]);
 				offset = (BITS_PER_LONG * map) + block;
 				offset *= pool->size;
 				goto ready;
 			}
 		}
 	}
 	page = pool_alloc_page(pool, GFP_ATOMIC);
 	if (!page) {
 		if (mem_flags & __GFP_WAIT) {
 			DECLARE_WAITQUEUE(wait, current);

 			__set_current_state(TASK_INTERRUPTIBLE);
 			__add_wait_queue(&pool->waitq, &wait);
 			spin_unlock_irqrestore(&pool->lock, flags);

 			schedule_timeout(POOL_TIMEOUT_JIFFIES);

 			spin_lock_irqsave(&pool->lock, flags);
 			__remove_wait_queue(&pool->waitq, &wait);
 			goto restart;
 		}
 		retval = NULL;
 		goto done;
 	}

 	clear_bit(0, &page->bitmap[0]);
 	offset = 0;
  ready:
 	page->in_use++;
 	retval = offset + page->vaddr;
 	*handle = offset + page->dma;
 #ifdef	CONFIG_DEBUG_SLAB
 	memset(retval, POOL_POISON_ALLOCATED, pool->size);
 #endif
  done:
 	spin_unlock_irqrestore(&pool->lock, flags);
 	return retval;
 }
 EXPORT_SYMBOL(dma_pool_alloc);

 static struct dma_page *pool_find_page(struct dma_pool *pool, dma_addr_t dma)
 {
 	unsigned long flags;
 	struct dma_page *page;

 	spin_lock_irqsave(&pool->lock, flags);
 	list_for_each_entry(page, &pool->page_list, page_list) {
 		if (dma < page->dma)
 			continue;
 		if (dma < (page->dma + pool->allocation))
 			goto done;
 	}
 	page = NULL;
  done:
 	spin_unlock_irqrestore(&pool->lock, flags);
 	return page;
 }

 /**
  * dma_pool_free - put block back into dma pool
  * @pool: the dma pool holding the block
  * @vaddr: virtual address of block
  * @dma: dma address of block
  *
  * Caller promises neither device nor driver will again touch this block
  * unless it is first re-allocated.
  */
 void dma_pool_free(struct dma_pool *pool, void *vaddr, dma_addr_t dma)
 {
 	struct dma_page *page;
 	unsigned long flags;
 	int map, block;

 	page = pool_find_page(pool, dma);
 	if (!page) {
 		if (pool->dev)
 			dev_err(pool->dev,
 				"dma_pool_free %s, %p/%lx (bad dma)\n",
 				pool->name, vaddr, (unsigned long)dma);
 		else
 			printk(KERN_ERR "dma_pool_free %s, %p/%lx (bad dma)\n",
 			       pool->name, vaddr, (unsigned long)dma);
 		return;
 	}

 	block = dma - page->dma;
 	block /= pool->size;
 	map = block / BITS_PER_LONG;
 	block %= BITS_PER_LONG;

 #ifdef	CONFIG_DEBUG_SLAB
 	if (((dma - page->dma) + (void *)page->vaddr) != vaddr) {
 		if (pool->dev)
 			dev_err(pool->dev,
 				"dma_pool_free %s, %p (bad vaddr)/%Lx\n",
 				pool->name, vaddr, (unsigned long long)dma);
 		else
 			printk(KERN_ERR
 			       "dma_pool_free %s, %p (bad vaddr)/%Lx\n",
 			       pool->name, vaddr, (unsigned long long)dma);
 		return;
 	}
 	if (page->bitmap[map] & (1UL << block)) {
 		if (pool->dev)
 			dev_err(pool->dev,
 				"dma_pool_free %s, dma %Lx already free\n",
 				pool->name, (unsigned long long)dma);
 		else
 			printk(KERN_ERR
 			       "dma_pool_free %s, dma %Lx already free\n",
 			       pool->name, (unsigned long long)dma);
 		return;
 	}
 	memset(vaddr, POOL_POISON_FREED, pool->size);
 #endif

 	spin_lock_irqsave(&pool->lock, flags);
 	page->in_use--;
 	set_bit(block, &page->bitmap[map]);
 	if (waitqueue_active(&pool->waitq))
 		wake_up_locked(&pool->waitq);
 	/*
 	 * Resist a temptation to do
 	 *    if (!is_page_busy(bpp, page->bitmap)) pool_free_page(pool, page);
 	 * Better have a few empty pages hang around.
 	 */
 	spin_unlock_irqrestore(&pool->lock, flags);
 }
 EXPORT_SYMBOL(dma_pool_free);

 /*
  * Managed DMA pool
  */
 static void dmam_pool_release(struct device *dev, void *res)
 {
 	struct dma_pool *pool = *(struct dma_pool **)res;

 	dma_pool_destroy(pool);
 }

 static int dmam_pool_match(struct device *dev, void *res, void *match_data)
 {
 	return *(struct dma_pool **)res == match_data;
 }

 /**
  * dmam_pool_create - Managed dma_pool_create()
  * @name: name of pool, for diagnostics
  * @dev: device that will be doing the DMA
  * @size: size of the blocks in this pool.
  * @align: alignment requirement for blocks; must be a power of two
  * @allocation: returned blocks won't cross this boundary (or zero)
  *
  * Managed dma_pool_create().  DMA pool created with this function is
  * automatically destroyed on driver detach.
  */
 struct dma_pool *dmam_pool_create(const char *name, struct device *dev,
 				  size_t size, size_t align, size_t allocation)
 {
 	struct dma_pool **ptr, *pool;

 	ptr = devres_alloc(dmam_pool_release, sizeof(*ptr), GFP_KERNEL);
 	if (!ptr)
 		return NULL;

 	pool = *ptr = dma_pool_create(name, dev, size, align, allocation);
 	if (pool)
 		devres_add(dev, ptr);
 	else
 		devres_free(ptr);

 	return pool;
 }
 EXPORT_SYMBOL(dmam_pool_create);

 /**
  * dmam_pool_destroy - Managed dma_pool_destroy()
  * @pool: dma pool that will be destroyed
  *
  * Managed dma_pool_destroy().
  */
 void dmam_pool_destroy(struct dma_pool *pool)
 {
 	struct device *dev = pool->dev;

 	dma_pool_destroy(pool);
 	WARN_ON(devres_destroy(dev, dmam_pool_release, dmam_pool_match, pool));
 }
 EXPORT_SYMBOL(dmam_pool_destroy);
	/*
	* DMA Pool allocator
	*
	* Copyright 2001 David Brownell
	* Copyright 2007 Intel Corporation
	* Author: Matthew Wilcox <willy@linux.intel.com>
	*
	* This software may be redistributed and/or modified under the terms of
	* the GNU General Public License ("GPL") version 2 as published by the
	* Free Software Foundation.
	*
	* This allocator returns small blocks of a given size which are DMA-able by
	* the given device. It uses the dma_alloc_coherent page allocator to get
	* new pages, then splits them up into blocks of the required size.
	* Many older drivers still have their own code to do this.
	*
	* The current design of this allocator is fairly simple. The pool is
	* represented by the 'struct dma_pool' which keeps a doubly-linked list of
	* allocated pages. Each page in the page_list is split into blocks of at
	* least 'size' bytes.
	*/

	#include <linux/device.h>
	#include <linux/dma-mapping.h>
	#include <linux/dmapool.h>
	#include <linux/kernel.h>
	#include <linux/list.h>
	#include <linux/module.h>
	#include <linux/mutex.h>
	#include <linux/poison.h>
	#include <linux/sched.h>
	#include <linux/slab.h>
	#include <linux/spinlock.h>
	#include <linux/string.h>
	#include <linux/types.h>
	#include <linux/wait.h>

	struct dma_pool { /* the pool */
	struct list_head page_list;
	spinlock_t lock;
	size_t blocks_per_page;
	size_t size;
	struct device *dev;
	size_t allocation;
	char name[32];
	wait_queue_head_t waitq;
	struct list_head pools;
	};

	struct dma_page { /* cacheable header for 'allocation' bytes */
	struct list_head page_list;
	void *vaddr;
	dma_addr_t dma;
	unsigned in_use;
	unsigned long bitmap[0];
	};

	#define POOL_TIMEOUT_JIFFIES ((100 /* msec / HZ) / 1000)

	static DEFINE_MUTEX(pools_lock);

	static ssize_t
	show_pools(struct device dev, struct device_attribute attr, char *buf)
	{
	unsigned temp;
	unsigned size;
	char *next;
	struct dma_page *page;
	struct dma_pool *pool;

	next = buf;
	size = PAGE_SIZE;

	temp = scnprintf(next, size, "poolinfo - 0.1\n");
	size -= temp;
	next += temp;

	mutex_lock(&pools_lock);
	list_for_each_entry(pool, &dev->dma_pools, pools) {
	unsigned pages = 0;
	unsigned blocks = 0;

	list_for_each_entry(page, &pool->page_list, page_list) {
	pages++;
	blocks += page->in_use;
	}

	/* per-pool info, no real statistics yet */
	temp = scnprintf(next, size, "%-16s %4u %4Zu %4Zu %2u\n",
	pool->name,
	blocks, pages * pool->blocks_per_page,
	pool->size, pages);
	size -= temp;
	next += temp;
	}
	mutex_unlock(&pools_lock);

	return PAGE_SIZE - size;
	}

	static DEVICE_ATTR(pools, S_IRUGO, show_pools, NULL);

	/**
	* dma_pool_create - Creates a pool of consistent memory blocks, for dma.
	* @name: name of pool, for diagnostics
	* @dev: device that will be doing the DMA
	* @size: size of the blocks in this pool.
	* @align: alignment requirement for blocks; must be a power of two
	* @allocation: returned blocks won't cross this boundary (or zero)
	* Context: !in_interrupt()
	*
	* Returns a dma allocation pool with the requested characteristics, or
	* null if one can't be created. Given one of these pools, dma_pool_alloc()
	* may be used to allocate memory. Such memory will all have "consistent"
	* DMA mappings, accessible by the device and its driver without using
	* cache flushing primitives. The actual size of blocks allocated may be
	* larger than requested because of alignment.
	*
	* If allocation is nonzero, objects returned from dma_pool_alloc() won't
	* cross that size boundary. This is useful for devices which have
	* addressing restrictions on individual DMA transfers, such as not crossing
	* boundaries of 4KBytes.
	*/
	struct dma_pool dma_pool_create(const char name, struct device *dev,
	size_t size, size_t align, size_t allocation)
	{
	struct dma_pool *retval;

	if (align == 0) {
	align = 1;
	} else if (align & (align - 1)) {
	return NULL;
	}

	if (size == 0)
	return NULL;

	if ((size % align) != 0)
	size = ALIGN(size, align);

	if (allocation == 0) {
	if (PAGE_SIZE < size)
	allocation = size;
	else
	allocation = PAGE_SIZE;
	/* FIXME: round up for less fragmentation */
	} else if (allocation < size)
	return NULL;

	if (!
	(retval =
	kmalloc_node(sizeof *retval, GFP_KERNEL, dev_to_node(dev))))
	return retval;

	strlcpy(retval->name, name, sizeof retval->name);

	retval->dev = dev;

	INIT_LIST_HEAD(&retval->page_list);
	spin_lock_init(&retval->lock);
	retval->size = size;
	retval->allocation = allocation;
	retval->blocks_per_page = allocation / size;
	init_waitqueue_head(&retval->waitq);

	if (dev) {
	int ret;

	mutex_lock(&pools_lock);
	if (list_empty(&dev->dma_pools))
	ret = device_create_file(dev, &dev_attr_pools);
	else
	ret = 0;
	/* note: not currently insisting "name" be unique */
	if (!ret)
	list_add(&retval->pools, &dev->dma_pools);
	else {
	kfree(retval);
	retval = NULL;
	}
	mutex_unlock(&pools_lock);
	} else
	INIT_LIST_HEAD(&retval->pools);

	return retval;
	}
	EXPORT_SYMBOL(dma_pool_create);

	static struct dma_page pool_alloc_page(struct dma_pool pool, gfp_t mem_flags)
	{
	struct dma_page *page;
	int mapsize;

	mapsize = pool->blocks_per_page;
	mapsize = (mapsize + BITS_PER_LONG - 1) / BITS_PER_LONG;
	mapsize *= sizeof(long);

	page = kmalloc(mapsize + sizeof *page, mem_flags);
	if (!page)
	return NULL;
	page->vaddr = dma_alloc_coherent(pool->dev,
	pool->allocation,
	&page->dma, mem_flags);
	if (page->vaddr) {
	memset(page->bitmap, 0xff, mapsize); /* bit set == free */
	#ifdef CONFIG_DEBUG_SLAB
	memset(page->vaddr, POOL_POISON_FREED, pool->allocation);
	#endif
	list_add(&page->page_list, &pool->page_list);
	page->in_use = 0;
	} else {
	kfree(page);
	page = NULL;
	}
	return page;
	}

	static inline int is_page_busy(int blocks, unsigned long *bitmap)
	{
	while (blocks > 0) {
	if (*bitmap++ != ~0UL)
	return 1;
	blocks -= BITS_PER_LONG;
	}
	return 0;
	}

	static void pool_free_page(struct dma_pool pool, struct dma_page page)
	{
	dma_addr_t dma = page->dma;

	#ifdef CONFIG_DEBUG_SLAB
	memset(page->vaddr, POOL_POISON_FREED, pool->allocation);
	#endif
	dma_free_coherent(pool->dev, pool->allocation, page->vaddr, dma);
	list_del(&page->page_list);
	kfree(page);
	}

	/**
	* dma_pool_destroy - destroys a pool of dma memory blocks.
	* @pool: dma pool that will be destroyed
	* Context: !in_interrupt()
	*
	* Caller guarantees that no more memory from the pool is in use,
	* and that nothing will try to use the pool after this call.
	*/
	void dma_pool_destroy(struct dma_pool *pool)
	{
	mutex_lock(&pools_lock);
	list_del(&pool->pools);
	if (pool->dev && list_empty(&pool->dev->dma_pools))
	device_remove_file(pool->dev, &dev_attr_pools);
	mutex_unlock(&pools_lock);

	while (!list_empty(&pool->page_list)) {
	struct dma_page *page;
	page = list_entry(pool->page_list.next,
	struct dma_page, page_list);
	if (is_page_busy(pool->blocks_per_page, page->bitmap)) {
	if (pool->dev)
	dev_err(pool->dev,
	"dma_pool_destroy %s, %p busy\n",
	pool->name, page->vaddr);
	else
	printk(KERN_ERR
	"dma_pool_destroy %s, %p busy\n",
	pool->name, page->vaddr);
	/* leak the still-in-use consistent memory */
	list_del(&page->page_list);
	kfree(page);
	} else
	pool_free_page(pool, page);
	}

	kfree(pool);
	}
	EXPORT_SYMBOL(dma_pool_destroy);

	/**
	* dma_pool_alloc - get a block of consistent memory
	* @pool: dma pool that will produce the block
	* @mem_flags: GFP_* bitmask
	* @handle: pointer to dma address of block
	*
	* This returns the kernel virtual address of a currently unused block,
	* and reports its dma address through the handle.
	* If such a memory block can't be allocated, %NULL is returned.
	*/
	void dma_pool_alloc(struct dma_pool pool, gfp_t mem_flags,
	dma_addr_t *handle)
	{
	unsigned long flags;
	struct dma_page *page;
	int map, block;
	size_t offset;
	void *retval;

	spin_lock_irqsave(&pool->lock, flags);
	restart:
	list_for_each_entry(page, &pool->page_list, page_list) {
	int i;
	/* only cachable accesses here ... */
	for (map = 0, i = 0;
	i < pool->blocks_per_page; i += BITS_PER_LONG, map++) {
	if (page->bitmap[map] == 0)
	continue;
	block = ffz(~page->bitmap[map]);
	if ((i + block) < pool->blocks_per_page) {
	clear_bit(block, &page->bitmap[map]);
	offset = (BITS_PER_LONG * map) + block;
	offset *= pool->size;
	goto ready;
	}
	}
	}
	page = pool_alloc_page(pool, GFP_ATOMIC);
	if (!page) {
	if (mem_flags & __GFP_WAIT) {
	DECLARE_WAITQUEUE(wait, current);

	__set_current_state(TASK_INTERRUPTIBLE);
	__add_wait_queue(&pool->waitq, &wait);
	spin_unlock_irqrestore(&pool->lock, flags);

	schedule_timeout(POOL_TIMEOUT_JIFFIES);

	spin_lock_irqsave(&pool->lock, flags);
	__remove_wait_queue(&pool->waitq, &wait);
	goto restart;
	}
	retval = NULL;
	goto done;
	}

	clear_bit(0, &page->bitmap[0]);
	offset = 0;
	ready:
	page->in_use++;
	retval = offset + page->vaddr;
	*handle = offset + page->dma;
	#ifdef CONFIG_DEBUG_SLAB
	memset(retval, POOL_POISON_ALLOCATED, pool->size);
	#endif
	done:
	spin_unlock_irqrestore(&pool->lock, flags);
	return retval;
	}
	EXPORT_SYMBOL(dma_pool_alloc);

	static struct dma_page pool_find_page(struct dma_pool pool, dma_addr_t dma)
	{
	unsigned long flags;
	struct dma_page *page;

	spin_lock_irqsave(&pool->lock, flags);
	list_for_each_entry(page, &pool->page_list, page_list) {
	if (dma < page->dma)
	continue;
	if (dma < (page->dma + pool->allocation))
	goto done;
	}
	page = NULL;
	done:
	spin_unlock_irqrestore(&pool->lock, flags);
	return page;
	}

	/**
	* dma_pool_free - put block back into dma pool
	* @pool: the dma pool holding the block
	* @vaddr: virtual address of block
	* @dma: dma address of block
	*
	* Caller promises neither device nor driver will again touch this block
	* unless it is first re-allocated.
	*/
	void dma_pool_free(struct dma_pool pool, void vaddr, dma_addr_t dma)
	{
	struct dma_page *page;
	unsigned long flags;
	int map, block;

	page = pool_find_page(pool, dma);
	if (!page) {
	if (pool->dev)
	dev_err(pool->dev,
	"dma_pool_free %s, %p/%lx (bad dma)\n",
	pool->name, vaddr, (unsigned long)dma);
	else
	printk(KERN_ERR "dma_pool_free %s, %p/%lx (bad dma)\n",
	pool->name, vaddr, (unsigned long)dma);
	return;
	}

	block = dma - page->dma;
	block /= pool->size;
	map = block / BITS_PER_LONG;
	block %= BITS_PER_LONG;

	#ifdef CONFIG_DEBUG_SLAB
	if (((dma - page->dma) + (void *)page->vaddr) != vaddr) {
	if (pool->dev)
	dev_err(pool->dev,
	"dma_pool_free %s, %p (bad vaddr)/%Lx\n",
	pool->name, vaddr, (unsigned long long)dma);
	else
	printk(KERN_ERR
	"dma_pool_free %s, %p (bad vaddr)/%Lx\n",
	pool->name, vaddr, (unsigned long long)dma);
	return;
	}
	if (page->bitmap[map] & (1UL << block)) {
	if (pool->dev)
	dev_err(pool->dev,
	"dma_pool_free %s, dma %Lx already free\n",
	pool->name, (unsigned long long)dma);
	else
	printk(KERN_ERR
	"dma_pool_free %s, dma %Lx already free\n",
	pool->name, (unsigned long long)dma);
	return;
	}
	memset(vaddr, POOL_POISON_FREED, pool->size);
	#endif

	spin_lock_irqsave(&pool->lock, flags);
	page->in_use--;
	set_bit(block, &page->bitmap[map]);
	if (waitqueue_active(&pool->waitq))
	wake_up_locked(&pool->waitq);
	/*
	* Resist a temptation to do
	* if (!is_page_busy(bpp, page->bitmap)) pool_free_page(pool, page);
	* Better have a few empty pages hang around.
	*/
	spin_unlock_irqrestore(&pool->lock, flags);
	}
	EXPORT_SYMBOL(dma_pool_free);

	/*
	* Managed DMA pool
	*/
	static void dmam_pool_release(struct device dev, void res)
	{
	struct dma_pool pool = (struct dma_pool **)res;

	dma_pool_destroy(pool);
	}

	static int dmam_pool_match(struct device dev, void res, void *match_data)
	{
	return (struct dma_pool *)res == match_data;
	}

	/**
	* dmam_pool_create - Managed dma_pool_create()
	* @name: name of pool, for diagnostics
	* @dev: device that will be doing the DMA
	* @size: size of the blocks in this pool.
	* @align: alignment requirement for blocks; must be a power of two
	* @allocation: returned blocks won't cross this boundary (or zero)
	*
	* Managed dma_pool_create(). DMA pool created with this function is
	* automatically destroyed on driver detach.
	*/
	struct dma_pool dmam_pool_create(const char name, struct device *dev,
	size_t size, size_t align, size_t allocation)
	{
	struct dma_pool *ptr, pool;

	ptr = devres_alloc(dmam_pool_release, sizeof(*ptr), GFP_KERNEL);
	if (!ptr)
	return NULL;

	pool = *ptr = dma_pool_create(name, dev, size, align, allocation);
	if (pool)
	devres_add(dev, ptr);
	else
	devres_free(ptr);

	return pool;
	}
	EXPORT_SYMBOL(dmam_pool_create);

	/**
	* dmam_pool_destroy - Managed dma_pool_destroy()
	* @pool: dma pool that will be destroyed
	*
	* Managed dma_pool_destroy().
	*/
	void dmam_pool_destroy(struct dma_pool *pool)
	{
	struct device *dev = pool->dev;

	dma_pool_destroy(pool);
	WARN_ON(devres_destroy(dev, dmam_pool_release, dmam_pool_match, pool));
	}
	EXPORT_SYMBOL(dmam_pool_destroy);