drivers/dma/dmaengine.c - kernel/msm - Gitiles

 /*
  * Copyright(c) 2004 - 2006 Intel Corporation. All rights reserved.
  *
  * 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.
  *
  * The full GNU General Public License is included in this distribution in the
  * file called COPYING.
  */

 /*
  * This code implements the DMA subsystem. It provides a HW-neutral interface
  * for other kernel code to use asynchronous memory copy capabilities,
  * if present, and allows different HW DMA drivers to register as providing
  * this capability.
  *
  * Due to the fact we are accelerating what is already a relatively fast
  * operation, the code goes to great lengths to avoid additional overhead,
  * such as locking.
  *
  * LOCKING:
  *
  * The subsystem keeps two global lists, dma_device_list and dma_client_list.
  * Both of these are protected by a mutex, dma_list_mutex.
  *
  * Each device has a channels list, which runs unlocked but is never modified
  * once the device is registered, it's just setup by the driver.
  *
  * Each client has a channels list, it's only modified under the client->lock
  * and in an RCU callback, so it's safe to read under rcu_read_lock().
  *
  * Each device has a kref, which is initialized to 1 when the device is
  * registered. A kref_put is done for each class_device registered.  When the
  * class_device is released, the coresponding kref_put is done in the release
  * method. Every time one of the device's channels is allocated to a client,
  * a kref_get occurs.  When the channel is freed, the coresponding kref_put
  * happens. The device's release function does a completion, so
  * unregister_device does a remove event, class_device_unregister, a kref_put
  * for the first reference, then waits on the completion for all other
  * references to finish.
  *
  * Each channel has an open-coded implementation of Rusty Russell's "bigref,"
  * with a kref and a per_cpu local_t.  A single reference is set when on an
  * ADDED event, and removed with a REMOVE event.  Net DMA client takes an
  * extra reference per outstanding transaction.  The relase function does a
  * kref_put on the device. -ChrisL
  */

 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/device.h>
 #include <linux/dmaengine.h>
 #include <linux/hardirq.h>
 #include <linux/spinlock.h>
 #include <linux/percpu.h>
 #include <linux/rcupdate.h>
 #include <linux/mutex.h>

 static DEFINE_MUTEX(dma_list_mutex);
 static LIST_HEAD(dma_device_list);
 static LIST_HEAD(dma_client_list);

 /* --- sysfs implementation --- */

 static ssize_t show_memcpy_count(struct class_device *cd, char *buf)
 {
 	struct dma_chan *chan = container_of(cd, struct dma_chan, class_dev);
 	unsigned long count = 0;
 	int i;

 	for_each_possible_cpu(i)
 		count += per_cpu_ptr(chan->local, i)->memcpy_count;

 	return sprintf(buf, "%lu\n", count);
 }

 static ssize_t show_bytes_transferred(struct class_device *cd, char *buf)
 {
 	struct dma_chan *chan = container_of(cd, struct dma_chan, class_dev);
 	unsigned long count = 0;
 	int i;

 	for_each_possible_cpu(i)
 		count += per_cpu_ptr(chan->local, i)->bytes_transferred;

 	return sprintf(buf, "%lu\n", count);
 }

 static ssize_t show_in_use(struct class_device *cd, char *buf)
 {
 	struct dma_chan *chan = container_of(cd, struct dma_chan, class_dev);

 	return sprintf(buf, "%d\n", (chan->client ? 1 : 0));
 }

 static struct class_device_attribute dma_class_attrs[] = {
 	__ATTR(memcpy_count, S_IRUGO, show_memcpy_count, NULL),
 	__ATTR(bytes_transferred, S_IRUGO, show_bytes_transferred, NULL),
 	__ATTR(in_use, S_IRUGO, show_in_use, NULL),
 	__ATTR_NULL
 };

 static void dma_async_device_cleanup(struct kref *kref);

 static void dma_class_dev_release(struct class_device *cd)
 {
 	struct dma_chan *chan = container_of(cd, struct dma_chan, class_dev);
 	kref_put(&chan->device->refcount, dma_async_device_cleanup);
 }

 static struct class dma_devclass = {
 	.name            = "dma",
 	.class_dev_attrs = dma_class_attrs,
 	.release = dma_class_dev_release,
 };

 /* --- client and device registration --- */

 /**
  * dma_client_chan_alloc - try to allocate a channel to a client
  * @client: &dma_client
  *
  * Called with dma_list_mutex held.
  */
 static struct dma_chan *dma_client_chan_alloc(struct dma_client *client)
 {
 	struct dma_device *device;
 	struct dma_chan *chan;
 	unsigned long flags;
 	int desc;	/* allocated descriptor count */

 	/* Find a channel, any DMA engine will do */
 	list_for_each_entry(device, &dma_device_list, global_node) {
 		list_for_each_entry(chan, &device->channels, device_node) {
 			if (chan->client)
 				continue;

 			desc = chan->device->device_alloc_chan_resources(chan);
 			if (desc >= 0) {
 				kref_get(&device->refcount);
 				kref_init(&chan->refcount);
 				chan->slow_ref = 0;
 				INIT_RCU_HEAD(&chan->rcu);
 				chan->client = client;
 				spin_lock_irqsave(&client->lock, flags);
 				list_add_tail_rcu(&chan->client_node,
 				                  &client->channels);
 				spin_unlock_irqrestore(&client->lock, flags);
 				return chan;
 			}
 		}
 	}

 	return NULL;
 }

 /**
  * dma_chan_cleanup - release a DMA channel's resources
  * @kref: kernel reference structure that contains the DMA channel device
  */
 void dma_chan_cleanup(struct kref *kref)
 {
 	struct dma_chan *chan = container_of(kref, struct dma_chan, refcount);
 	chan->device->device_free_chan_resources(chan);
 	chan->client = NULL;
 	kref_put(&chan->device->refcount, dma_async_device_cleanup);
 }

 static void dma_chan_free_rcu(struct rcu_head *rcu)
 {
 	struct dma_chan *chan = container_of(rcu, struct dma_chan, rcu);
 	int bias = 0x7FFFFFFF;
 	int i;
 	for_each_possible_cpu(i)
 		bias -= local_read(&per_cpu_ptr(chan->local, i)->refcount);
 	atomic_sub(bias, &chan->refcount.refcount);
 	kref_put(&chan->refcount, dma_chan_cleanup);
 }

 static void dma_client_chan_free(struct dma_chan *chan)
 {
 	atomic_add(0x7FFFFFFF, &chan->refcount.refcount);
 	chan->slow_ref = 1;
 	call_rcu(&chan->rcu, dma_chan_free_rcu);
 }

 /**
  * dma_chans_rebalance - reallocate channels to clients
  *
  * When the number of DMA channel in the system changes,
  * channels need to be rebalanced among clients.
  */
 static void dma_chans_rebalance(void)
 {
 	struct dma_client *client;
 	struct dma_chan *chan;
 	unsigned long flags;

 	mutex_lock(&dma_list_mutex);

 	list_for_each_entry(client, &dma_client_list, global_node) {
 		while (client->chans_desired > client->chan_count) {
 			chan = dma_client_chan_alloc(client);
 			if (!chan)
 				break;
 			client->chan_count++;
 			client->event_callback(client,
 	                                       chan,
 	                                       DMA_RESOURCE_ADDED);
 		}
 		while (client->chans_desired < client->chan_count) {
 			spin_lock_irqsave(&client->lock, flags);
 			chan = list_entry(client->channels.next,
 			                  struct dma_chan,
 			                  client_node);
 			list_del_rcu(&chan->client_node);
 			spin_unlock_irqrestore(&client->lock, flags);
 			client->chan_count--;
 			client->event_callback(client,
 			                       chan,
 			                       DMA_RESOURCE_REMOVED);
 			dma_client_chan_free(chan);
 		}
 	}

 	mutex_unlock(&dma_list_mutex);
 }

 /**
  * dma_async_client_register - allocate and register a &dma_client
  * @event_callback: callback for notification of channel addition/removal
  */
 struct dma_client *dma_async_client_register(dma_event_callback event_callback)
 {
 	struct dma_client *client;

 	client = kzalloc(sizeof(*client), GFP_KERNEL);
 	if (!client)
 		return NULL;

 	INIT_LIST_HEAD(&client->channels);
 	spin_lock_init(&client->lock);
 	client->chans_desired = 0;
 	client->chan_count = 0;
 	client->event_callback = event_callback;

 	mutex_lock(&dma_list_mutex);
 	list_add_tail(&client->global_node, &dma_client_list);
 	mutex_unlock(&dma_list_mutex);

 	return client;
 }

 /**
  * dma_async_client_unregister - unregister a client and free the &dma_client
  * @client: &dma_client to free
  *
  * Force frees any allocated DMA channels, frees the &dma_client memory
  */
 void dma_async_client_unregister(struct dma_client *client)
 {
 	struct dma_chan *chan;

 	if (!client)
 		return;

 	rcu_read_lock();
 	list_for_each_entry_rcu(chan, &client->channels, client_node)
 		dma_client_chan_free(chan);
 	rcu_read_unlock();

 	mutex_lock(&dma_list_mutex);
 	list_del(&client->global_node);
 	mutex_unlock(&dma_list_mutex);

 	kfree(client);
 	dma_chans_rebalance();
 }

 /**
  * dma_async_client_chan_request - request DMA channels
  * @client: &dma_client
  * @number: count of DMA channels requested
  *
  * Clients call dma_async_client_chan_request() to specify how many
  * DMA channels they need, 0 to free all currently allocated.
  * The resulting allocations/frees are indicated to the client via the
  * event callback.
  */
 void dma_async_client_chan_request(struct dma_client *client,
 			unsigned int number)
 {
 	client->chans_desired = number;
 	dma_chans_rebalance();
 }

 /**
  * dma_async_device_register - registers DMA devices found
  * @device: &dma_device
  */
 int dma_async_device_register(struct dma_device *device)
 {
 	static int id;
 	int chancnt = 0;
 	struct dma_chan* chan;

 	if (!device)
 		return -ENODEV;

 	init_completion(&device->done);
 	kref_init(&device->refcount);
 	device->dev_id = id++;

 	/* represent channels in sysfs. Probably want devs too */
 	list_for_each_entry(chan, &device->channels, device_node) {
 		chan->local = alloc_percpu(typeof(*chan->local));
 		if (chan->local == NULL)
 			continue;

 		chan->chan_id = chancnt++;
 		chan->class_dev.class = &dma_devclass;
 		chan->class_dev.dev = NULL;
 		snprintf(chan->class_dev.class_id, BUS_ID_SIZE, "dma%dchan%d",
 		         device->dev_id, chan->chan_id);

 		kref_get(&device->refcount);
 		class_device_register(&chan->class_dev);
 	}

 	mutex_lock(&dma_list_mutex);
 	list_add_tail(&device->global_node, &dma_device_list);
 	mutex_unlock(&dma_list_mutex);

 	dma_chans_rebalance();

 	return 0;
 }

 /**
  * dma_async_device_cleanup - function called when all references are released
  * @kref: kernel reference object
  */
 static void dma_async_device_cleanup(struct kref *kref)
 {
 	struct dma_device *device;

 	device = container_of(kref, struct dma_device, refcount);
 	complete(&device->done);
 }

 /**
  * dma_async_device_unregister - unregisters DMA devices
  * @device: &dma_device
  */
 void dma_async_device_unregister(struct dma_device *device)
 {
 	struct dma_chan *chan;
 	unsigned long flags;

 	mutex_lock(&dma_list_mutex);
 	list_del(&device->global_node);
 	mutex_unlock(&dma_list_mutex);

 	list_for_each_entry(chan, &device->channels, device_node) {
 		if (chan->client) {
 			spin_lock_irqsave(&chan->client->lock, flags);
 			list_del(&chan->client_node);
 			chan->client->chan_count--;
 			spin_unlock_irqrestore(&chan->client->lock, flags);
 			chan->client->event_callback(chan->client,
 			                             chan,
 			                             DMA_RESOURCE_REMOVED);
 			dma_client_chan_free(chan);
 		}
 		class_device_unregister(&chan->class_dev);
 	}
 	dma_chans_rebalance();

 	kref_put(&device->refcount, dma_async_device_cleanup);
 	wait_for_completion(&device->done);
 }

 static int __init dma_bus_init(void)
 {
 	mutex_init(&dma_list_mutex);
 	return class_register(&dma_devclass);
 }

 subsys_initcall(dma_bus_init);

 EXPORT_SYMBOL(dma_async_client_register);
 EXPORT_SYMBOL(dma_async_client_unregister);
 EXPORT_SYMBOL(dma_async_client_chan_request);
 EXPORT_SYMBOL(dma_async_memcpy_buf_to_buf);
 EXPORT_SYMBOL(dma_async_memcpy_buf_to_pg);
 EXPORT_SYMBOL(dma_async_memcpy_pg_to_pg);
 EXPORT_SYMBOL(dma_async_memcpy_complete);
 EXPORT_SYMBOL(dma_async_memcpy_issue_pending);
 EXPORT_SYMBOL(dma_async_device_register);
 EXPORT_SYMBOL(dma_async_device_unregister);
 EXPORT_SYMBOL(dma_chan_cleanup);
	/*
	* Copyright(c) 2004 - 2006 Intel Corporation. All rights reserved.
	*
	* 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.
	*
	* The full GNU General Public License is included in this distribution in the
	* file called COPYING.
	*/

	/*
	* This code implements the DMA subsystem. It provides a HW-neutral interface
	* for other kernel code to use asynchronous memory copy capabilities,
	* if present, and allows different HW DMA drivers to register as providing
	* this capability.
	*
	* Due to the fact we are accelerating what is already a relatively fast
	* operation, the code goes to great lengths to avoid additional overhead,
	* such as locking.
	*
	* LOCKING:
	*
	* The subsystem keeps two global lists, dma_device_list and dma_client_list.
	* Both of these are protected by a mutex, dma_list_mutex.
	*
	* Each device has a channels list, which runs unlocked but is never modified
	* once the device is registered, it's just setup by the driver.
	*
	* Each client has a channels list, it's only modified under the client->lock
	* and in an RCU callback, so it's safe to read under rcu_read_lock().
	*
	* Each device has a kref, which is initialized to 1 when the device is
	* registered. A kref_put is done for each class_device registered. When the
	* class_device is released, the coresponding kref_put is done in the release
	* method. Every time one of the device's channels is allocated to a client,
	* a kref_get occurs. When the channel is freed, the coresponding kref_put
	* happens. The device's release function does a completion, so
	* unregister_device does a remove event, class_device_unregister, a kref_put
	* for the first reference, then waits on the completion for all other
	* references to finish.
	*
	* Each channel has an open-coded implementation of Rusty Russell's "bigref,"
	* with a kref and a per_cpu local_t. A single reference is set when on an
	* ADDED event, and removed with a REMOVE event. Net DMA client takes an
	* extra reference per outstanding transaction. The relase function does a
	* kref_put on the device. -ChrisL
	*/

	#include <linux/init.h>
	#include <linux/module.h>
	#include <linux/device.h>
	#include <linux/dmaengine.h>
	#include <linux/hardirq.h>
	#include <linux/spinlock.h>
	#include <linux/percpu.h>
	#include <linux/rcupdate.h>
	#include <linux/mutex.h>

	static DEFINE_MUTEX(dma_list_mutex);
	static LIST_HEAD(dma_device_list);
	static LIST_HEAD(dma_client_list);

	/* --- sysfs implementation --- */

	static ssize_t show_memcpy_count(struct class_device cd, char buf)
	{
	struct dma_chan *chan = container_of(cd, struct dma_chan, class_dev);
	unsigned long count = 0;
	int i;

	for_each_possible_cpu(i)
	count += per_cpu_ptr(chan->local, i)->memcpy_count;

	return sprintf(buf, "%lu\n", count);
	}

	static ssize_t show_bytes_transferred(struct class_device cd, char buf)
	{
	struct dma_chan *chan = container_of(cd, struct dma_chan, class_dev);
	unsigned long count = 0;
	int i;

	for_each_possible_cpu(i)
	count += per_cpu_ptr(chan->local, i)->bytes_transferred;

	return sprintf(buf, "%lu\n", count);
	}

	static ssize_t show_in_use(struct class_device cd, char buf)
	{
	struct dma_chan *chan = container_of(cd, struct dma_chan, class_dev);

	return sprintf(buf, "%d\n", (chan->client ? 1 : 0));
	}

	static struct class_device_attribute dma_class_attrs[] = {
	__ATTR(memcpy_count, S_IRUGO, show_memcpy_count, NULL),
	__ATTR(bytes_transferred, S_IRUGO, show_bytes_transferred, NULL),
	__ATTR(in_use, S_IRUGO, show_in_use, NULL),
	__ATTR_NULL
	};

	static void dma_async_device_cleanup(struct kref *kref);

	static void dma_class_dev_release(struct class_device *cd)
	{
	struct dma_chan *chan = container_of(cd, struct dma_chan, class_dev);
	kref_put(&chan->device->refcount, dma_async_device_cleanup);
	}

	static struct class dma_devclass = {
	.name = "dma",
	.class_dev_attrs = dma_class_attrs,
	.release = dma_class_dev_release,
	};

	/* --- client and device registration --- */

	/**
	* dma_client_chan_alloc - try to allocate a channel to a client
	* @client: &dma_client
	*
	* Called with dma_list_mutex held.
	*/
	static struct dma_chan dma_client_chan_alloc(struct dma_client client)
	{
	struct dma_device *device;
	struct dma_chan *chan;
	unsigned long flags;
	int desc; /* allocated descriptor count */

	/* Find a channel, any DMA engine will do */
	list_for_each_entry(device, &dma_device_list, global_node) {
	list_for_each_entry(chan, &device->channels, device_node) {
	if (chan->client)
	continue;

	desc = chan->device->device_alloc_chan_resources(chan);
	if (desc >= 0) {
	kref_get(&device->refcount);
	kref_init(&chan->refcount);
	chan->slow_ref = 0;
	INIT_RCU_HEAD(&chan->rcu);
	chan->client = client;
	spin_lock_irqsave(&client->lock, flags);
	list_add_tail_rcu(&chan->client_node,
	&client->channels);
	spin_unlock_irqrestore(&client->lock, flags);
	return chan;
	}
	}
	}

	return NULL;
	}

	/**
	* dma_chan_cleanup - release a DMA channel's resources
	* @kref: kernel reference structure that contains the DMA channel device
	*/
	void dma_chan_cleanup(struct kref *kref)
	{
	struct dma_chan *chan = container_of(kref, struct dma_chan, refcount);
	chan->device->device_free_chan_resources(chan);
	chan->client = NULL;
	kref_put(&chan->device->refcount, dma_async_device_cleanup);
	}

	static void dma_chan_free_rcu(struct rcu_head *rcu)
	{
	struct dma_chan *chan = container_of(rcu, struct dma_chan, rcu);
	int bias = 0x7FFFFFFF;
	int i;
	for_each_possible_cpu(i)
	bias -= local_read(&per_cpu_ptr(chan->local, i)->refcount);
	atomic_sub(bias, &chan->refcount.refcount);
	kref_put(&chan->refcount, dma_chan_cleanup);
	}

	static void dma_client_chan_free(struct dma_chan *chan)
	{
	atomic_add(0x7FFFFFFF, &chan->refcount.refcount);
	chan->slow_ref = 1;
	call_rcu(&chan->rcu, dma_chan_free_rcu);
	}

	/**
	* dma_chans_rebalance - reallocate channels to clients
	*
	* When the number of DMA channel in the system changes,
	* channels need to be rebalanced among clients.
	*/
	static void dma_chans_rebalance(void)
	{
	struct dma_client *client;
	struct dma_chan *chan;
	unsigned long flags;

	mutex_lock(&dma_list_mutex);

	list_for_each_entry(client, &dma_client_list, global_node) {
	while (client->chans_desired > client->chan_count) {
	chan = dma_client_chan_alloc(client);
	if (!chan)
	break;
	client->chan_count++;
	client->event_callback(client,
	chan,
	DMA_RESOURCE_ADDED);
	}
	while (client->chans_desired < client->chan_count) {
	spin_lock_irqsave(&client->lock, flags);
	chan = list_entry(client->channels.next,
	struct dma_chan,
	client_node);
	list_del_rcu(&chan->client_node);
	spin_unlock_irqrestore(&client->lock, flags);
	client->chan_count--;
	client->event_callback(client,
	chan,
	DMA_RESOURCE_REMOVED);
	dma_client_chan_free(chan);
	}
	}

	mutex_unlock(&dma_list_mutex);
	}

	/**
	* dma_async_client_register - allocate and register a &dma_client
	* @event_callback: callback for notification of channel addition/removal
	*/
	struct dma_client *dma_async_client_register(dma_event_callback event_callback)
	{
	struct dma_client *client;

	client = kzalloc(sizeof(*client), GFP_KERNEL);
	if (!client)
	return NULL;

	INIT_LIST_HEAD(&client->channels);
	spin_lock_init(&client->lock);
	client->chans_desired = 0;
	client->chan_count = 0;
	client->event_callback = event_callback;

	mutex_lock(&dma_list_mutex);
	list_add_tail(&client->global_node, &dma_client_list);
	mutex_unlock(&dma_list_mutex);

	return client;
	}

	/**
	* dma_async_client_unregister - unregister a client and free the &dma_client
	* @client: &dma_client to free
	*
	* Force frees any allocated DMA channels, frees the &dma_client memory
	*/
	void dma_async_client_unregister(struct dma_client *client)
	{
	struct dma_chan *chan;

	if (!client)
	return;

	rcu_read_lock();
	list_for_each_entry_rcu(chan, &client->channels, client_node)
	dma_client_chan_free(chan);
	rcu_read_unlock();

	mutex_lock(&dma_list_mutex);
	list_del(&client->global_node);
	mutex_unlock(&dma_list_mutex);

	kfree(client);
	dma_chans_rebalance();
	}

	/**
	* dma_async_client_chan_request - request DMA channels
	* @client: &dma_client
	* @number: count of DMA channels requested
	*
	* Clients call dma_async_client_chan_request() to specify how many
	* DMA channels they need, 0 to free all currently allocated.
	* The resulting allocations/frees are indicated to the client via the
	* event callback.
	*/
	void dma_async_client_chan_request(struct dma_client *client,
	unsigned int number)
	{
	client->chans_desired = number;
	dma_chans_rebalance();
	}

	/**
	* dma_async_device_register - registers DMA devices found
	* @device: &dma_device
	*/
	int dma_async_device_register(struct dma_device *device)
	{
	static int id;
	int chancnt = 0;
	struct dma_chan* chan;

	if (!device)
	return -ENODEV;

	init_completion(&device->done);
	kref_init(&device->refcount);
	device->dev_id = id++;

	/* represent channels in sysfs. Probably want devs too */
	list_for_each_entry(chan, &device->channels, device_node) {
	chan->local = alloc_percpu(typeof(*chan->local));
	if (chan->local == NULL)
	continue;

	chan->chan_id = chancnt++;
	chan->class_dev.class = &dma_devclass;
	chan->class_dev.dev = NULL;
	snprintf(chan->class_dev.class_id, BUS_ID_SIZE, "dma%dchan%d",
	device->dev_id, chan->chan_id);

	kref_get(&device->refcount);
	class_device_register(&chan->class_dev);
	}

	mutex_lock(&dma_list_mutex);
	list_add_tail(&device->global_node, &dma_device_list);
	mutex_unlock(&dma_list_mutex);

	dma_chans_rebalance();

	return 0;
	}

	/**
	* dma_async_device_cleanup - function called when all references are released
	* @kref: kernel reference object
	*/
	static void dma_async_device_cleanup(struct kref *kref)
	{
	struct dma_device *device;

	device = container_of(kref, struct dma_device, refcount);
	complete(&device->done);
	}

	/**
	* dma_async_device_unregister - unregisters DMA devices
	* @device: &dma_device
	*/
	void dma_async_device_unregister(struct dma_device *device)
	{
	struct dma_chan *chan;
	unsigned long flags;

	mutex_lock(&dma_list_mutex);
	list_del(&device->global_node);
	mutex_unlock(&dma_list_mutex);

	list_for_each_entry(chan, &device->channels, device_node) {
	if (chan->client) {
	spin_lock_irqsave(&chan->client->lock, flags);
	list_del(&chan->client_node);
	chan->client->chan_count--;
	spin_unlock_irqrestore(&chan->client->lock, flags);
	chan->client->event_callback(chan->client,
	chan,
	DMA_RESOURCE_REMOVED);
	dma_client_chan_free(chan);
	}
	class_device_unregister(&chan->class_dev);
	}
	dma_chans_rebalance();

	kref_put(&device->refcount, dma_async_device_cleanup);
	wait_for_completion(&device->done);
	}

	static int __init dma_bus_init(void)
	{
	mutex_init(&dma_list_mutex);
	return class_register(&dma_devclass);
	}

	subsys_initcall(dma_bus_init);

	EXPORT_SYMBOL(dma_async_client_register);
	EXPORT_SYMBOL(dma_async_client_unregister);
	EXPORT_SYMBOL(dma_async_client_chan_request);
	EXPORT_SYMBOL(dma_async_memcpy_buf_to_buf);
	EXPORT_SYMBOL(dma_async_memcpy_buf_to_pg);
	EXPORT_SYMBOL(dma_async_memcpy_pg_to_pg);
	EXPORT_SYMBOL(dma_async_memcpy_complete);
	EXPORT_SYMBOL(dma_async_memcpy_issue_pending);
	EXPORT_SYMBOL(dma_async_device_register);
	EXPORT_SYMBOL(dma_async_device_unregister);
	EXPORT_SYMBOL(dma_chan_cleanup);