v4.19.13 snapshot.
diff --git a/drivers/iio/buffer/industrialio-buffer-dma.c b/drivers/iio/buffer/industrialio-buffer-dma.c
new file mode 100644
index 0000000..b32bf57
--- /dev/null
+++ b/drivers/iio/buffer/industrialio-buffer-dma.c
@@ -0,0 +1,684 @@
+/*
+ * 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_impl.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, EPOLLIN | EPOLLRDNORM);
+}
+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, EPOLLIN | EPOLLRDNORM);
+}
+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 < ARRAY_SIZE(queue->fileio.blocks); 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 < ARRAY_SIZE(queue->fileio.blocks); 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, unsigned 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");