Linux-libre 4.5-gnu

1 files changed, 683 insertions, 0 deletions

diff --git a/drivers/iio/buffer/industrialio-buffer-dma.c b/drivers/iio/buffer/industrialio-buffer-dma.c
new file mode 100644
index 000000000..212cbedc7
--- /dev/null
+++ b/drivers/iio/buffer/industrialio-buffer-dma.c
@@ -0,0 +1,683 @@
+/*
+ * Copyright 2013-2015 Analog Devices Inc.
+ *  Author: Lars-Peter Clausen <lars@metafoo.de>
+ *
+ * Licensed under the GPL-2.
+ */
+
+#include <linux/slab.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/device.h>
+#include <linux/workqueue.h>
+#include <linux/mutex.h>
+#include <linux/sched.h>
+#include <linux/poll.h>
+#include <linux/iio/buffer.h>
+#include <linux/iio/buffer-dma.h>
+#include <linux/dma-mapping.h>
+#include <linux/sizes.h>
+
+/*
+ * For DMA buffers the storage is sub-divided into so called blocks. Each block
+ * has its own memory buffer. The size of the block is the granularity at which
+ * memory is exchanged between the hardware and the application. Increasing the
+ * basic unit of data exchange from one sample to one block decreases the
+ * management overhead that is associated with each sample. E.g. if we say the
+ * management overhead for one exchange is x and the unit of exchange is one
+ * sample the overhead will be x for each sample. Whereas when using a block
+ * which contains n samples the overhead per sample is reduced to x/n. This
+ * allows to achieve much higher samplerates than what can be sustained with
+ * the one sample approach.
+ *
+ * Blocks are exchanged between the DMA controller and the application via the
+ * means of two queues. The incoming queue and the outgoing queue. Blocks on the
+ * incoming queue are waiting for the DMA controller to pick them up and fill
+ * them with data. Block on the outgoing queue have been filled with data and
+ * are waiting for the application to dequeue them and read the data.
+ *
+ * A block can be in one of the following states:
+ *  * Owned by the application. In this state the application can read data from
+ *    the block.
+ *  * On the incoming list: Blocks on the incoming list are queued up to be
+ *    processed by the DMA controller.
+ *  * Owned by the DMA controller: The DMA controller is processing the block
+ *    and filling it with data.
+ *  * On the outgoing list: Blocks on the outgoing list have been successfully
+ *    processed by the DMA controller and contain data. They can be dequeued by
+ *    the application.
+ *  * Dead: A block that is dead has been marked as to be freed. It might still
+ *    be owned by either the application or the DMA controller at the moment.
+ *    But once they are done processing it instead of going to either the
+ *    incoming or outgoing queue the block will be freed.
+ *
+ * In addition to this blocks are reference counted and the memory associated
+ * with both the block structure as well as the storage memory for the block
+ * will be freed when the last reference to the block is dropped. This means a
+ * block must not be accessed without holding a reference.
+ *
+ * The iio_dma_buffer implementation provides a generic infrastructure for
+ * managing the blocks.
+ *
+ * A driver for a specific piece of hardware that has DMA capabilities need to
+ * implement the submit() callback from the iio_dma_buffer_ops structure. This
+ * callback is supposed to initiate the DMA transfer copying data from the
+ * converter to the memory region of the block. Once the DMA transfer has been
+ * completed the driver must call iio_dma_buffer_block_done() for the completed
+ * block.
+ *
+ * Prior to this it must set the bytes_used field of the block contains
+ * the actual number of bytes in the buffer. Typically this will be equal to the
+ * size of the block, but if the DMA hardware has certain alignment requirements
+ * for the transfer length it might choose to use less than the full size. In
+ * either case it is expected that bytes_used is a multiple of the bytes per
+ * datum, i.e. the block must not contain partial samples.
+ *
+ * The driver must call iio_dma_buffer_block_done() for each block it has
+ * received through its submit_block() callback, even if it does not actually
+ * perform a DMA transfer for the block, e.g. because the buffer was disabled
+ * before the block transfer was started. In this case it should set bytes_used
+ * to 0.
+ *
+ * In addition it is recommended that a driver implements the abort() callback.
+ * It will be called when the buffer is disabled and can be used to cancel
+ * pending and stop active transfers.
+ *
+ * The specific driver implementation should use the default callback
+ * implementations provided by this module for the iio_buffer_access_funcs
+ * struct. It may overload some callbacks with custom variants if the hardware
+ * has special requirements that are not handled by the generic functions. If a
+ * driver chooses to overload a callback it has to ensure that the generic
+ * callback is called from within the custom callback.
+ */
+
+static void iio_buffer_block_release(struct kref *kref)
+{
+	struct iio_dma_buffer_block *block = container_of(kref,
+		struct iio_dma_buffer_block, kref);
+
+	WARN_ON(block->state != IIO_BLOCK_STATE_DEAD);
+
+	dma_free_coherent(block->queue->dev, PAGE_ALIGN(block->size),
+					block->vaddr, block->phys_addr);
+
+	iio_buffer_put(&block->queue->buffer);
+	kfree(block);
+}
+
+static void iio_buffer_block_get(struct iio_dma_buffer_block *block)
+{
+	kref_get(&block->kref);
+}
+
+static void iio_buffer_block_put(struct iio_dma_buffer_block *block)
+{
+	kref_put(&block->kref, iio_buffer_block_release);
+}
+
+/*
+ * dma_free_coherent can sleep, hence we need to take some special care to be
+ * able to drop a reference from an atomic context.
+ */
+static LIST_HEAD(iio_dma_buffer_dead_blocks);
+static DEFINE_SPINLOCK(iio_dma_buffer_dead_blocks_lock);
+
+static void iio_dma_buffer_cleanup_worker(struct work_struct *work)
+{
+	struct iio_dma_buffer_block *block, *_block;
+	LIST_HEAD(block_list);
+
+	spin_lock_irq(&iio_dma_buffer_dead_blocks_lock);
+	list_splice_tail_init(&iio_dma_buffer_dead_blocks, &block_list);
+	spin_unlock_irq(&iio_dma_buffer_dead_blocks_lock);
+
+	list_for_each_entry_safe(block, _block, &block_list, head)
+		iio_buffer_block_release(&block->kref);
+}
+static DECLARE_WORK(iio_dma_buffer_cleanup_work, iio_dma_buffer_cleanup_worker);
+
+static void iio_buffer_block_release_atomic(struct kref *kref)
+{
+	struct iio_dma_buffer_block *block;
+	unsigned long flags;
+
+	block = container_of(kref, struct iio_dma_buffer_block, kref);
+
+	spin_lock_irqsave(&iio_dma_buffer_dead_blocks_lock, flags);
+	list_add_tail(&block->head, &iio_dma_buffer_dead_blocks);
+	spin_unlock_irqrestore(&iio_dma_buffer_dead_blocks_lock, flags);
+
+	schedule_work(&iio_dma_buffer_cleanup_work);
+}
+
+/*
+ * Version of iio_buffer_block_put() that can be called from atomic context
+ */
+static void iio_buffer_block_put_atomic(struct iio_dma_buffer_block *block)
+{
+	kref_put(&block->kref, iio_buffer_block_release_atomic);
+}
+
+static struct iio_dma_buffer_queue *iio_buffer_to_queue(struct iio_buffer *buf)
+{
+	return container_of(buf, struct iio_dma_buffer_queue, buffer);
+}
+
+static struct iio_dma_buffer_block *iio_dma_buffer_alloc_block(
+	struct iio_dma_buffer_queue *queue, size_t size)
+{
+	struct iio_dma_buffer_block *block;
+
+	block = kzalloc(sizeof(*block), GFP_KERNEL);
+	if (!block)
+		return NULL;
+
+	block->vaddr = dma_alloc_coherent(queue->dev, PAGE_ALIGN(size),
+		&block->phys_addr, GFP_KERNEL);
+	if (!block->vaddr) {
+		kfree(block);
+		return NULL;
+	}
+
+	block->size = size;
+	block->state = IIO_BLOCK_STATE_DEQUEUED;
+	block->queue = queue;
+	INIT_LIST_HEAD(&block->head);
+	kref_init(&block->kref);
+
+	iio_buffer_get(&queue->buffer);
+
+	return block;
+}
+
+static void _iio_dma_buffer_block_done(struct iio_dma_buffer_block *block)
+{
+	struct iio_dma_buffer_queue *queue = block->queue;
+
+	/*
+	 * The buffer has already been freed by the application, just drop the
+	 * reference.
+	 */
+	if (block->state != IIO_BLOCK_STATE_DEAD) {
+		block->state = IIO_BLOCK_STATE_DONE;
+		list_add_tail(&block->head, &queue->outgoing);
+	}
+}
+
+/**
+ * iio_dma_buffer_block_done() - Indicate that a block has been completed
+ * @block: The completed block
+ *
+ * Should be called when the DMA controller has finished handling the block to
+ * pass back ownership of the block to the queue.
+ */
+void iio_dma_buffer_block_done(struct iio_dma_buffer_block *block)
+{
+	struct iio_dma_buffer_queue *queue = block->queue;
+	unsigned long flags;
+
+	spin_lock_irqsave(&queue->list_lock, flags);
+	_iio_dma_buffer_block_done(block);
+	spin_unlock_irqrestore(&queue->list_lock, flags);
+
+	iio_buffer_block_put_atomic(block);
+	wake_up_interruptible_poll(&queue->buffer.pollq, POLLIN | POLLRDNORM);
+}
+EXPORT_SYMBOL_GPL(iio_dma_buffer_block_done);
+
+/**
+ * iio_dma_buffer_block_list_abort() - Indicate that a list block has been
+ *   aborted
+ * @queue: Queue for which to complete blocks.
+ * @list: List of aborted blocks. All blocks in this list must be from @queue.
+ *
+ * Typically called from the abort() callback after the DMA controller has been
+ * stopped. This will set bytes_used to 0 for each block in the list and then
+ * hand the blocks back to the queue.
+ */
+void iio_dma_buffer_block_list_abort(struct iio_dma_buffer_queue *queue,
+	struct list_head *list)
+{
+	struct iio_dma_buffer_block *block, *_block;
+	unsigned long flags;
+
+	spin_lock_irqsave(&queue->list_lock, flags);
+	list_for_each_entry_safe(block, _block, list, head) {
+		list_del(&block->head);
+		block->bytes_used = 0;
+		_iio_dma_buffer_block_done(block);
+		iio_buffer_block_put_atomic(block);
+	}
+	spin_unlock_irqrestore(&queue->list_lock, flags);
+
+	wake_up_interruptible_poll(&queue->buffer.pollq, POLLIN | POLLRDNORM);
+}
+EXPORT_SYMBOL_GPL(iio_dma_buffer_block_list_abort);
+
+static bool iio_dma_block_reusable(struct iio_dma_buffer_block *block)
+{
+	/*
+	 * If the core owns the block it can be re-used. This should be the
+	 * default case when enabling the buffer, unless the DMA controller does
+	 * not support abort and has not given back the block yet.
+	 */
+	switch (block->state) {
+	case IIO_BLOCK_STATE_DEQUEUED:
+	case IIO_BLOCK_STATE_QUEUED:
+	case IIO_BLOCK_STATE_DONE:
+		return true;
+	default:
+		return false;
+	}
+}
+
+/**
+ * iio_dma_buffer_request_update() - DMA buffer request_update callback
+ * @buffer: The buffer which to request an update
+ *
+ * Should be used as the iio_dma_buffer_request_update() callback for
+ * iio_buffer_access_ops struct for DMA buffers.
+ */
+int iio_dma_buffer_request_update(struct iio_buffer *buffer)
+{
+	struct iio_dma_buffer_queue *queue = iio_buffer_to_queue(buffer);
+	struct iio_dma_buffer_block *block;
+	bool try_reuse = false;
+	size_t size;
+	int ret = 0;
+	int i;
+
+	/*
+	 * Split the buffer into two even parts. This is used as a double
+	 * buffering scheme with usually one block at a time being used by the
+	 * DMA and the other one by the application.
+	 */
+	size = DIV_ROUND_UP(queue->buffer.bytes_per_datum *
+		queue->buffer.length, 2);
+
+	mutex_lock(&queue->lock);
+
+	/* Allocations are page aligned */
+	if (PAGE_ALIGN(queue->fileio.block_size) == PAGE_ALIGN(size))
+		try_reuse = true;
+
+	queue->fileio.block_size = size;
+	queue->fileio.active_block = NULL;
+
+	spin_lock_irq(&queue->list_lock);
+	for (i = 0; i < 2; i++) {
+		block = queue->fileio.blocks[i];
+
+		/* If we can't re-use it free it */
+		if (block && (!iio_dma_block_reusable(block) || !try_reuse))
+			block->state = IIO_BLOCK_STATE_DEAD;
+	}
+
+	/*
+	 * At this point all blocks are either owned by the core or marked as
+	 * dead. This means we can reset the lists without having to fear
+	 * corrution.
+	 */
+	INIT_LIST_HEAD(&queue->outgoing);
+	spin_unlock_irq(&queue->list_lock);
+
+	INIT_LIST_HEAD(&queue->incoming);
+
+	for (i = 0; i < 2; i++) {
+		if (queue->fileio.blocks[i]) {
+			block = queue->fileio.blocks[i];
+			if (block->state == IIO_BLOCK_STATE_DEAD) {
+				/* Could not reuse it */
+				iio_buffer_block_put(block);
+				block = NULL;
+			} else {
+				block->size = size;
+			}
+		} else {
+			block = NULL;
+		}
+
+		if (!block) {
+			block = iio_dma_buffer_alloc_block(queue, size);
+			if (!block) {
+				ret = -ENOMEM;
+				goto out_unlock;
+			}
+			queue->fileio.blocks[i] = block;
+		}
+
+		block->state = IIO_BLOCK_STATE_QUEUED;
+		list_add_tail(&block->head, &queue->incoming);
+	}
+
+out_unlock:
+	mutex_unlock(&queue->lock);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(iio_dma_buffer_request_update);
+
+static void iio_dma_buffer_submit_block(struct iio_dma_buffer_queue *queue,
+	struct iio_dma_buffer_block *block)
+{
+	int ret;
+
+	/*
+	 * If the hardware has already been removed we put the block into
+	 * limbo. It will neither be on the incoming nor outgoing list, nor will
+	 * it ever complete. It will just wait to be freed eventually.
+	 */
+	if (!queue->ops)
+		return;
+
+	block->state = IIO_BLOCK_STATE_ACTIVE;
+	iio_buffer_block_get(block);
+	ret = queue->ops->submit(queue, block);
+	if (ret) {
+		/*
+		 * This is a bit of a problem and there is not much we can do
+		 * other then wait for the buffer to be disabled and re-enabled
+		 * and try again. But it should not really happen unless we run
+		 * out of memory or something similar.
+		 *
+		 * TODO: Implement support in the IIO core to allow buffers to
+		 * notify consumers that something went wrong and the buffer
+		 * should be disabled.
+		 */
+		iio_buffer_block_put(block);
+	}
+}
+
+/**
+ * iio_dma_buffer_enable() - Enable DMA buffer
+ * @buffer: IIO buffer to enable
+ * @indio_dev: IIO device the buffer is attached to
+ *
+ * Needs to be called when the device that the buffer is attached to starts
+ * sampling. Typically should be the iio_buffer_access_ops enable callback.
+ *
+ * This will allocate the DMA buffers and start the DMA transfers.
+ */
+int iio_dma_buffer_enable(struct iio_buffer *buffer,
+	struct iio_dev *indio_dev)
+{
+	struct iio_dma_buffer_queue *queue = iio_buffer_to_queue(buffer);
+	struct iio_dma_buffer_block *block, *_block;
+
+	mutex_lock(&queue->lock);
+	queue->active = true;
+	list_for_each_entry_safe(block, _block, &queue->incoming, head) {
+		list_del(&block->head);
+		iio_dma_buffer_submit_block(queue, block);
+	}
+	mutex_unlock(&queue->lock);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(iio_dma_buffer_enable);
+
+/**
+ * iio_dma_buffer_disable() - Disable DMA buffer
+ * @buffer: IIO DMA buffer to disable
+ * @indio_dev: IIO device the buffer is attached to
+ *
+ * Needs to be called when the device that the buffer is attached to stops
+ * sampling. Typically should be the iio_buffer_access_ops disable callback.
+ */
+int iio_dma_buffer_disable(struct iio_buffer *buffer,
+	struct iio_dev *indio_dev)
+{
+	struct iio_dma_buffer_queue *queue = iio_buffer_to_queue(buffer);
+
+	mutex_lock(&queue->lock);
+	queue->active = false;
+
+	if (queue->ops && queue->ops->abort)
+		queue->ops->abort(queue);
+	mutex_unlock(&queue->lock);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(iio_dma_buffer_disable);
+
+static void iio_dma_buffer_enqueue(struct iio_dma_buffer_queue *queue,
+	struct iio_dma_buffer_block *block)
+{
+	if (block->state == IIO_BLOCK_STATE_DEAD) {
+		iio_buffer_block_put(block);
+	} else if (queue->active) {
+		iio_dma_buffer_submit_block(queue, block);
+	} else {
+		block->state = IIO_BLOCK_STATE_QUEUED;
+		list_add_tail(&block->head, &queue->incoming);
+	}
+}
+
+static struct iio_dma_buffer_block *iio_dma_buffer_dequeue(
+	struct iio_dma_buffer_queue *queue)
+{
+	struct iio_dma_buffer_block *block;
+
+	spin_lock_irq(&queue->list_lock);
+	block = list_first_entry_or_null(&queue->outgoing, struct
+		iio_dma_buffer_block, head);
+	if (block != NULL) {
+		list_del(&block->head);
+		block->state = IIO_BLOCK_STATE_DEQUEUED;
+	}
+	spin_unlock_irq(&queue->list_lock);
+
+	return block;
+}
+
+/**
+ * iio_dma_buffer_read() - DMA buffer read callback
+ * @buffer: Buffer to read form
+ * @n: Number of bytes to read
+ * @user_buffer: Userspace buffer to copy the data to
+ *
+ * Should be used as the read_first_n callback for iio_buffer_access_ops
+ * struct for DMA buffers.
+ */
+int iio_dma_buffer_read(struct iio_buffer *buffer, size_t n,
+	char __user *user_buffer)
+{
+	struct iio_dma_buffer_queue *queue = iio_buffer_to_queue(buffer);
+	struct iio_dma_buffer_block *block;
+	int ret;
+
+	if (n < buffer->bytes_per_datum)
+		return -EINVAL;
+
+	mutex_lock(&queue->lock);
+
+	if (!queue->fileio.active_block) {
+		block = iio_dma_buffer_dequeue(queue);
+		if (block == NULL) {
+			ret = 0;
+			goto out_unlock;
+		}
+		queue->fileio.pos = 0;
+		queue->fileio.active_block = block;
+	} else {
+		block = queue->fileio.active_block;
+	}
+
+	n = rounddown(n, buffer->bytes_per_datum);
+	if (n > block->bytes_used - queue->fileio.pos)
+		n = block->bytes_used - queue->fileio.pos;
+
+	if (copy_to_user(user_buffer, block->vaddr + queue->fileio.pos, n)) {
+		ret = -EFAULT;
+		goto out_unlock;
+	}
+
+	queue->fileio.pos += n;
+
+	if (queue->fileio.pos == block->bytes_used) {
+		queue->fileio.active_block = NULL;
+		iio_dma_buffer_enqueue(queue, block);
+	}
+
+	ret = n;
+
+out_unlock:
+	mutex_unlock(&queue->lock);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(iio_dma_buffer_read);
+
+/**
+ * iio_dma_buffer_data_available() - DMA buffer data_available callback
+ * @buf: Buffer to check for data availability
+ *
+ * Should be used as the data_available callback for iio_buffer_access_ops
+ * struct for DMA buffers.
+ */
+size_t iio_dma_buffer_data_available(struct iio_buffer *buf)
+{
+	struct iio_dma_buffer_queue *queue = iio_buffer_to_queue(buf);
+	struct iio_dma_buffer_block *block;
+	size_t data_available = 0;
+
+	/*
+	 * For counting the available bytes we'll use the size of the block not
+	 * the number of actual bytes available in the block. Otherwise it is
+	 * possible that we end up with a value that is lower than the watermark
+	 * but won't increase since all blocks are in use.
+	 */
+
+	mutex_lock(&queue->lock);
+	if (queue->fileio.active_block)
+		data_available += queue->fileio.active_block->size;
+
+	spin_lock_irq(&queue->list_lock);
+	list_for_each_entry(block, &queue->outgoing, head)
+		data_available += block->size;
+	spin_unlock_irq(&queue->list_lock);
+	mutex_unlock(&queue->lock);
+
+	return data_available;
+}
+EXPORT_SYMBOL_GPL(iio_dma_buffer_data_available);
+
+/**
+ * iio_dma_buffer_set_bytes_per_datum() - DMA buffer set_bytes_per_datum callback
+ * @buffer: Buffer to set the bytes-per-datum for
+ * @bpd: The new bytes-per-datum value
+ *
+ * Should be used as the set_bytes_per_datum callback for iio_buffer_access_ops
+ * struct for DMA buffers.
+ */
+int iio_dma_buffer_set_bytes_per_datum(struct iio_buffer *buffer, size_t bpd)
+{
+	buffer->bytes_per_datum = bpd;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(iio_dma_buffer_set_bytes_per_datum);
+
+/**
+ * iio_dma_buffer_set_length - DMA buffer set_length callback
+ * @buffer: Buffer to set the length for
+ * @length: The new buffer length
+ *
+ * Should be used as the set_length callback for iio_buffer_access_ops
+ * struct for DMA buffers.
+ */
+int iio_dma_buffer_set_length(struct iio_buffer *buffer, int length)
+{
+	/* Avoid an invalid state */
+	if (length < 2)
+		length = 2;
+	buffer->length = length;
+	buffer->watermark = length / 2;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(iio_dma_buffer_set_length);
+
+/**
+ * iio_dma_buffer_init() - Initialize DMA buffer queue
+ * @queue: Buffer to initialize
+ * @dev: DMA device
+ * @ops: DMA buffer queue callback operations
+ *
+ * The DMA device will be used by the queue to do DMA memory allocations. So it
+ * should refer to the device that will perform the DMA to ensure that
+ * allocations are done from a memory region that can be accessed by the device.
+ */
+int iio_dma_buffer_init(struct iio_dma_buffer_queue *queue,
+	struct device *dev, const struct iio_dma_buffer_ops *ops)
+{
+	iio_buffer_init(&queue->buffer);
+	queue->buffer.length = PAGE_SIZE;
+	queue->buffer.watermark = queue->buffer.length / 2;
+	queue->dev = dev;
+	queue->ops = ops;
+
+	INIT_LIST_HEAD(&queue->incoming);
+	INIT_LIST_HEAD(&queue->outgoing);
+
+	mutex_init(&queue->lock);
+	spin_lock_init(&queue->list_lock);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(iio_dma_buffer_init);
+
+/**
+ * iio_dma_buffer_exit() - Cleanup DMA buffer queue
+ * @queue: Buffer to cleanup
+ *
+ * After this function has completed it is safe to free any resources that are
+ * associated with the buffer and are accessed inside the callback operations.
+ */
+void iio_dma_buffer_exit(struct iio_dma_buffer_queue *queue)
+{
+	unsigned int i;
+
+	mutex_lock(&queue->lock);
+
+	spin_lock_irq(&queue->list_lock);
+	for (i = 0; i < ARRAY_SIZE(queue->fileio.blocks); i++) {
+		if (!queue->fileio.blocks[i])
+			continue;
+		queue->fileio.blocks[i]->state = IIO_BLOCK_STATE_DEAD;
+	}
+	INIT_LIST_HEAD(&queue->outgoing);
+	spin_unlock_irq(&queue->list_lock);
+
+	INIT_LIST_HEAD(&queue->incoming);
+
+	for (i = 0; i < ARRAY_SIZE(queue->fileio.blocks); i++) {
+		if (!queue->fileio.blocks[i])
+			continue;
+		iio_buffer_block_put(queue->fileio.blocks[i]);
+		queue->fileio.blocks[i] = NULL;
+	}
+	queue->fileio.active_block = NULL;
+	queue->ops = NULL;
+
+	mutex_unlock(&queue->lock);
+}
+EXPORT_SYMBOL_GPL(iio_dma_buffer_exit);
+
+/**
+ * iio_dma_buffer_release() - Release final buffer resources
+ * @queue: Buffer to release
+ *
+ * Frees resources that can't yet be freed in iio_dma_buffer_exit(). Should be
+ * called in the buffers release callback implementation right before freeing
+ * the memory associated with the buffer.
+ */
+void iio_dma_buffer_release(struct iio_dma_buffer_queue *queue)
+{
+	mutex_destroy(&queue->lock);
+}
+EXPORT_SYMBOL_GPL(iio_dma_buffer_release);
+
+MODULE_AUTHOR("Lars-Peter Clausen <lars@metafoo.de>");
+MODULE_DESCRIPTION("DMA buffer for the IIO framework");
+MODULE_LICENSE("GPL v2");