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1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Copyright 2013-2015 Analog Devices Inc.
4 * Author: Lars-Peter Clausen <lars@metafoo.de>
5 */
6
7#include <linux/slab.h>
8#include <linux/kernel.h>
9#include <linux/module.h>
10#include <linux/device.h>
11#include <linux/workqueue.h>
12#include <linux/mutex.h>
13#include <linux/sched.h>
14#include <linux/poll.h>
15#include <linux/iio/buffer_impl.h>
16#include <linux/iio/buffer-dma.h>
17#include <linux/dma-mapping.h>
18#include <linux/sizes.h>
19
20/*
21 * For DMA buffers the storage is sub-divided into so called blocks. Each block
22 * has its own memory buffer. The size of the block is the granularity at which
23 * memory is exchanged between the hardware and the application. Increasing the
24 * basic unit of data exchange from one sample to one block decreases the
25 * management overhead that is associated with each sample. E.g. if we say the
26 * management overhead for one exchange is x and the unit of exchange is one
27 * sample the overhead will be x for each sample. Whereas when using a block
28 * which contains n samples the overhead per sample is reduced to x/n. This
29 * allows to achieve much higher samplerates than what can be sustained with
30 * the one sample approach.
31 *
32 * Blocks are exchanged between the DMA controller and the application via the
33 * means of two queues. The incoming queue and the outgoing queue. Blocks on the
34 * incoming queue are waiting for the DMA controller to pick them up and fill
35 * them with data. Block on the outgoing queue have been filled with data and
36 * are waiting for the application to dequeue them and read the data.
37 *
38 * A block can be in one of the following states:
39 * * Owned by the application. In this state the application can read data from
40 * the block.
41 * * On the incoming list: Blocks on the incoming list are queued up to be
42 * processed by the DMA controller.
43 * * Owned by the DMA controller: The DMA controller is processing the block
44 * and filling it with data.
45 * * On the outgoing list: Blocks on the outgoing list have been successfully
46 * processed by the DMA controller and contain data. They can be dequeued by
47 * the application.
48 * * Dead: A block that is dead has been marked as to be freed. It might still
49 * be owned by either the application or the DMA controller at the moment.
50 * But once they are done processing it instead of going to either the
51 * incoming or outgoing queue the block will be freed.
52 *
53 * In addition to this blocks are reference counted and the memory associated
54 * with both the block structure as well as the storage memory for the block
55 * will be freed when the last reference to the block is dropped. This means a
56 * block must not be accessed without holding a reference.
57 *
58 * The iio_dma_buffer implementation provides a generic infrastructure for
59 * managing the blocks.
60 *
61 * A driver for a specific piece of hardware that has DMA capabilities need to
62 * implement the submit() callback from the iio_dma_buffer_ops structure. This
63 * callback is supposed to initiate the DMA transfer copying data from the
64 * converter to the memory region of the block. Once the DMA transfer has been
65 * completed the driver must call iio_dma_buffer_block_done() for the completed
66 * block.
67 *
68 * Prior to this it must set the bytes_used field of the block contains
69 * the actual number of bytes in the buffer. Typically this will be equal to the
70 * size of the block, but if the DMA hardware has certain alignment requirements
71 * for the transfer length it might choose to use less than the full size. In
72 * either case it is expected that bytes_used is a multiple of the bytes per
73 * datum, i.e. the block must not contain partial samples.
74 *
75 * The driver must call iio_dma_buffer_block_done() for each block it has
76 * received through its submit_block() callback, even if it does not actually
77 * perform a DMA transfer for the block, e.g. because the buffer was disabled
78 * before the block transfer was started. In this case it should set bytes_used
79 * to 0.
80 *
81 * In addition it is recommended that a driver implements the abort() callback.
82 * It will be called when the buffer is disabled and can be used to cancel
83 * pending and stop active transfers.
84 *
85 * The specific driver implementation should use the default callback
86 * implementations provided by this module for the iio_buffer_access_funcs
87 * struct. It may overload some callbacks with custom variants if the hardware
88 * has special requirements that are not handled by the generic functions. If a
89 * driver chooses to overload a callback it has to ensure that the generic
90 * callback is called from within the custom callback.
91 */
92
93static void iio_buffer_block_release(struct kref *kref)
94{
95 struct iio_dma_buffer_block *block = container_of(kref,
96 struct iio_dma_buffer_block, kref);
97
98 WARN_ON(block->state != IIO_BLOCK_STATE_DEAD);
99
100 dma_free_coherent(block->queue->dev, PAGE_ALIGN(block->size),
101 block->vaddr, block->phys_addr);
102
103 iio_buffer_put(&block->queue->buffer);
104 kfree(block);
105}
106
107static void iio_buffer_block_get(struct iio_dma_buffer_block *block)
108{
109 kref_get(&block->kref);
110}
111
112static void iio_buffer_block_put(struct iio_dma_buffer_block *block)
113{
114 kref_put(&block->kref, iio_buffer_block_release);
115}
116
117/*
118 * dma_free_coherent can sleep, hence we need to take some special care to be
119 * able to drop a reference from an atomic context.
120 */
121static LIST_HEAD(iio_dma_buffer_dead_blocks);
122static DEFINE_SPINLOCK(iio_dma_buffer_dead_blocks_lock);
123
124static void iio_dma_buffer_cleanup_worker(struct work_struct *work)
125{
126 struct iio_dma_buffer_block *block, *_block;
127 LIST_HEAD(block_list);
128
129 spin_lock_irq(&iio_dma_buffer_dead_blocks_lock);
130 list_splice_tail_init(&iio_dma_buffer_dead_blocks, &block_list);
131 spin_unlock_irq(&iio_dma_buffer_dead_blocks_lock);
132
133 list_for_each_entry_safe(block, _block, &block_list, head)
134 iio_buffer_block_release(&block->kref);
135}
136static DECLARE_WORK(iio_dma_buffer_cleanup_work, iio_dma_buffer_cleanup_worker);
137
138static void iio_buffer_block_release_atomic(struct kref *kref)
139{
140 struct iio_dma_buffer_block *block;
141 unsigned long flags;
142
143 block = container_of(kref, struct iio_dma_buffer_block, kref);
144
145 spin_lock_irqsave(&iio_dma_buffer_dead_blocks_lock, flags);
146 list_add_tail(&block->head, &iio_dma_buffer_dead_blocks);
147 spin_unlock_irqrestore(&iio_dma_buffer_dead_blocks_lock, flags);
148
149 schedule_work(&iio_dma_buffer_cleanup_work);
150}
151
152/*
153 * Version of iio_buffer_block_put() that can be called from atomic context
154 */
155static void iio_buffer_block_put_atomic(struct iio_dma_buffer_block *block)
156{
157 kref_put(&block->kref, iio_buffer_block_release_atomic);
158}
159
160static struct iio_dma_buffer_queue *iio_buffer_to_queue(struct iio_buffer *buf)
161{
162 return container_of(buf, struct iio_dma_buffer_queue, buffer);
163}
164
165static struct iio_dma_buffer_block *iio_dma_buffer_alloc_block(
166 struct iio_dma_buffer_queue *queue, size_t size)
167{
168 struct iio_dma_buffer_block *block;
169
170 block = kzalloc(sizeof(*block), GFP_KERNEL);
171 if (!block)
172 return NULL;
173
174 block->vaddr = dma_alloc_coherent(queue->dev, PAGE_ALIGN(size),
175 &block->phys_addr, GFP_KERNEL);
176 if (!block->vaddr) {
177 kfree(block);
178 return NULL;
179 }
180
181 block->size = size;
182 block->state = IIO_BLOCK_STATE_DEQUEUED;
183 block->queue = queue;
184 INIT_LIST_HEAD(&block->head);
185 kref_init(&block->kref);
186
187 iio_buffer_get(&queue->buffer);
188
189 return block;
190}
191
192static void _iio_dma_buffer_block_done(struct iio_dma_buffer_block *block)
193{
194 struct iio_dma_buffer_queue *queue = block->queue;
195
196 /*
197 * The buffer has already been freed by the application, just drop the
198 * reference.
199 */
200 if (block->state != IIO_BLOCK_STATE_DEAD) {
201 block->state = IIO_BLOCK_STATE_DONE;
202 list_add_tail(&block->head, &queue->outgoing);
203 }
204}
205
206/**
207 * iio_dma_buffer_block_done() - Indicate that a block has been completed
208 * @block: The completed block
209 *
210 * Should be called when the DMA controller has finished handling the block to
211 * pass back ownership of the block to the queue.
212 */
213void iio_dma_buffer_block_done(struct iio_dma_buffer_block *block)
214{
215 struct iio_dma_buffer_queue *queue = block->queue;
216 unsigned long flags;
217
218 spin_lock_irqsave(&queue->list_lock, flags);
219 _iio_dma_buffer_block_done(block);
220 spin_unlock_irqrestore(&queue->list_lock, flags);
221
222 iio_buffer_block_put_atomic(block);
223 wake_up_interruptible_poll(&queue->buffer.pollq, EPOLLIN | EPOLLRDNORM);
224}
225EXPORT_SYMBOL_GPL(iio_dma_buffer_block_done);
226
227/**
228 * iio_dma_buffer_block_list_abort() - Indicate that a list block has been
229 * aborted
230 * @queue: Queue for which to complete blocks.
231 * @list: List of aborted blocks. All blocks in this list must be from @queue.
232 *
233 * Typically called from the abort() callback after the DMA controller has been
234 * stopped. This will set bytes_used to 0 for each block in the list and then
235 * hand the blocks back to the queue.
236 */
237void iio_dma_buffer_block_list_abort(struct iio_dma_buffer_queue *queue,
238 struct list_head *list)
239{
240 struct iio_dma_buffer_block *block, *_block;
241 unsigned long flags;
242
243 spin_lock_irqsave(&queue->list_lock, flags);
244 list_for_each_entry_safe(block, _block, list, head) {
245 list_del(&block->head);
246 block->bytes_used = 0;
247 _iio_dma_buffer_block_done(block);
248 iio_buffer_block_put_atomic(block);
249 }
250 spin_unlock_irqrestore(&queue->list_lock, flags);
251
252 wake_up_interruptible_poll(&queue->buffer.pollq, EPOLLIN | EPOLLRDNORM);
253}
254EXPORT_SYMBOL_GPL(iio_dma_buffer_block_list_abort);
255
256static bool iio_dma_block_reusable(struct iio_dma_buffer_block *block)
257{
258 /*
259 * If the core owns the block it can be re-used. This should be the
260 * default case when enabling the buffer, unless the DMA controller does
261 * not support abort and has not given back the block yet.
262 */
263 switch (block->state) {
264 case IIO_BLOCK_STATE_DEQUEUED:
265 case IIO_BLOCK_STATE_QUEUED:
266 case IIO_BLOCK_STATE_DONE:
267 return true;
268 default:
269 return false;
270 }
271}
272
273/**
274 * iio_dma_buffer_request_update() - DMA buffer request_update callback
275 * @buffer: The buffer which to request an update
276 *
277 * Should be used as the iio_dma_buffer_request_update() callback for
278 * iio_buffer_access_ops struct for DMA buffers.
279 */
280int iio_dma_buffer_request_update(struct iio_buffer *buffer)
281{
282 struct iio_dma_buffer_queue *queue = iio_buffer_to_queue(buffer);
283 struct iio_dma_buffer_block *block;
284 bool try_reuse = false;
285 size_t size;
286 int ret = 0;
287 int i;
288
289 /*
290 * Split the buffer into two even parts. This is used as a double
291 * buffering scheme with usually one block at a time being used by the
292 * DMA and the other one by the application.
293 */
294 size = DIV_ROUND_UP(queue->buffer.bytes_per_datum *
295 queue->buffer.length, 2);
296
297 mutex_lock(&queue->lock);
298
299 /* Allocations are page aligned */
300 if (PAGE_ALIGN(queue->fileio.block_size) == PAGE_ALIGN(size))
301 try_reuse = true;
302
303 queue->fileio.block_size = size;
304 queue->fileio.active_block = NULL;
305
306 spin_lock_irq(&queue->list_lock);
307 for (i = 0; i < ARRAY_SIZE(queue->fileio.blocks); i++) {
308 block = queue->fileio.blocks[i];
309
310 /* If we can't re-use it free it */
311 if (block && (!iio_dma_block_reusable(block) || !try_reuse))
312 block->state = IIO_BLOCK_STATE_DEAD;
313 }
314
315 /*
316 * At this point all blocks are either owned by the core or marked as
317 * dead. This means we can reset the lists without having to fear
318 * corrution.
319 */
320 INIT_LIST_HEAD(&queue->outgoing);
321 spin_unlock_irq(&queue->list_lock);
322
323 INIT_LIST_HEAD(&queue->incoming);
324
325 for (i = 0; i < ARRAY_SIZE(queue->fileio.blocks); i++) {
326 if (queue->fileio.blocks[i]) {
327 block = queue->fileio.blocks[i];
328 if (block->state == IIO_BLOCK_STATE_DEAD) {
329 /* Could not reuse it */
330 iio_buffer_block_put(block);
331 block = NULL;
332 } else {
333 block->size = size;
334 }
335 } else {
336 block = NULL;
337 }
338
339 if (!block) {
340 block = iio_dma_buffer_alloc_block(queue, size);
341 if (!block) {
342 ret = -ENOMEM;
343 goto out_unlock;
344 }
345 queue->fileio.blocks[i] = block;
346 }
347
348 block->state = IIO_BLOCK_STATE_QUEUED;
349 list_add_tail(&block->head, &queue->incoming);
350 }
351
352out_unlock:
353 mutex_unlock(&queue->lock);
354
355 return ret;
356}
357EXPORT_SYMBOL_GPL(iio_dma_buffer_request_update);
358
359static void iio_dma_buffer_submit_block(struct iio_dma_buffer_queue *queue,
360 struct iio_dma_buffer_block *block)
361{
362 int ret;
363
364 /*
365 * If the hardware has already been removed we put the block into
366 * limbo. It will neither be on the incoming nor outgoing list, nor will
367 * it ever complete. It will just wait to be freed eventually.
368 */
369 if (!queue->ops)
370 return;
371
372 block->state = IIO_BLOCK_STATE_ACTIVE;
373 iio_buffer_block_get(block);
374 ret = queue->ops->submit(queue, block);
375 if (ret) {
376 /*
377 * This is a bit of a problem and there is not much we can do
378 * other then wait for the buffer to be disabled and re-enabled
379 * and try again. But it should not really happen unless we run
380 * out of memory or something similar.
381 *
382 * TODO: Implement support in the IIO core to allow buffers to
383 * notify consumers that something went wrong and the buffer
384 * should be disabled.
385 */
386 iio_buffer_block_put(block);
387 }
388}
389
390/**
391 * iio_dma_buffer_enable() - Enable DMA buffer
392 * @buffer: IIO buffer to enable
393 * @indio_dev: IIO device the buffer is attached to
394 *
395 * Needs to be called when the device that the buffer is attached to starts
396 * sampling. Typically should be the iio_buffer_access_ops enable callback.
397 *
398 * This will allocate the DMA buffers and start the DMA transfers.
399 */
400int iio_dma_buffer_enable(struct iio_buffer *buffer,
401 struct iio_dev *indio_dev)
402{
403 struct iio_dma_buffer_queue *queue = iio_buffer_to_queue(buffer);
404 struct iio_dma_buffer_block *block, *_block;
405
406 mutex_lock(&queue->lock);
407 queue->active = true;
408 list_for_each_entry_safe(block, _block, &queue->incoming, head) {
409 list_del(&block->head);
410 iio_dma_buffer_submit_block(queue, block);
411 }
412 mutex_unlock(&queue->lock);
413
414 return 0;
415}
416EXPORT_SYMBOL_GPL(iio_dma_buffer_enable);
417
418/**
419 * iio_dma_buffer_disable() - Disable DMA buffer
420 * @buffer: IIO DMA buffer to disable
421 * @indio_dev: IIO device the buffer is attached to
422 *
423 * Needs to be called when the device that the buffer is attached to stops
424 * sampling. Typically should be the iio_buffer_access_ops disable callback.
425 */
426int iio_dma_buffer_disable(struct iio_buffer *buffer,
427 struct iio_dev *indio_dev)
428{
429 struct iio_dma_buffer_queue *queue = iio_buffer_to_queue(buffer);
430
431 mutex_lock(&queue->lock);
432 queue->active = false;
433
434 if (queue->ops && queue->ops->abort)
435 queue->ops->abort(queue);
436 mutex_unlock(&queue->lock);
437
438 return 0;
439}
440EXPORT_SYMBOL_GPL(iio_dma_buffer_disable);
441
442static void iio_dma_buffer_enqueue(struct iio_dma_buffer_queue *queue,
443 struct iio_dma_buffer_block *block)
444{
445 if (block->state == IIO_BLOCK_STATE_DEAD) {
446 iio_buffer_block_put(block);
447 } else if (queue->active) {
448 iio_dma_buffer_submit_block(queue, block);
449 } else {
450 block->state = IIO_BLOCK_STATE_QUEUED;
451 list_add_tail(&block->head, &queue->incoming);
452 }
453}
454
455static struct iio_dma_buffer_block *iio_dma_buffer_dequeue(
456 struct iio_dma_buffer_queue *queue)
457{
458 struct iio_dma_buffer_block *block;
459
460 spin_lock_irq(&queue->list_lock);
461 block = list_first_entry_or_null(&queue->outgoing, struct
462 iio_dma_buffer_block, head);
463 if (block != NULL) {
464 list_del(&block->head);
465 block->state = IIO_BLOCK_STATE_DEQUEUED;
466 }
467 spin_unlock_irq(&queue->list_lock);
468
469 return block;
470}
471
472/**
473 * iio_dma_buffer_read() - DMA buffer read callback
474 * @buffer: Buffer to read form
475 * @n: Number of bytes to read
476 * @user_buffer: Userspace buffer to copy the data to
477 *
478 * Should be used as the read callback for iio_buffer_access_ops
479 * struct for DMA buffers.
480 */
481int iio_dma_buffer_read(struct iio_buffer *buffer, size_t n,
482 char __user *user_buffer)
483{
484 struct iio_dma_buffer_queue *queue = iio_buffer_to_queue(buffer);
485 struct iio_dma_buffer_block *block;
486 int ret;
487
488 if (n < buffer->bytes_per_datum)
489 return -EINVAL;
490
491 mutex_lock(&queue->lock);
492
493 if (!queue->fileio.active_block) {
494 block = iio_dma_buffer_dequeue(queue);
495 if (block == NULL) {
496 ret = 0;
497 goto out_unlock;
498 }
499 queue->fileio.pos = 0;
500 queue->fileio.active_block = block;
501 } else {
502 block = queue->fileio.active_block;
503 }
504
505 n = rounddown(n, buffer->bytes_per_datum);
506 if (n > block->bytes_used - queue->fileio.pos)
507 n = block->bytes_used - queue->fileio.pos;
508
509 if (copy_to_user(user_buffer, block->vaddr + queue->fileio.pos, n)) {
510 ret = -EFAULT;
511 goto out_unlock;
512 }
513
514 queue->fileio.pos += n;
515
516 if (queue->fileio.pos == block->bytes_used) {
517 queue->fileio.active_block = NULL;
518 iio_dma_buffer_enqueue(queue, block);
519 }
520
521 ret = n;
522
523out_unlock:
524 mutex_unlock(&queue->lock);
525
526 return ret;
527}
528EXPORT_SYMBOL_GPL(iio_dma_buffer_read);
529
530/**
531 * iio_dma_buffer_data_available() - DMA buffer data_available callback
532 * @buf: Buffer to check for data availability
533 *
534 * Should be used as the data_available callback for iio_buffer_access_ops
535 * struct for DMA buffers.
536 */
537size_t iio_dma_buffer_data_available(struct iio_buffer *buf)
538{
539 struct iio_dma_buffer_queue *queue = iio_buffer_to_queue(buf);
540 struct iio_dma_buffer_block *block;
541 size_t data_available = 0;
542
543 /*
544 * For counting the available bytes we'll use the size of the block not
545 * the number of actual bytes available in the block. Otherwise it is
546 * possible that we end up with a value that is lower than the watermark
547 * but won't increase since all blocks are in use.
548 */
549
550 mutex_lock(&queue->lock);
551 if (queue->fileio.active_block)
552 data_available += queue->fileio.active_block->size;
553
554 spin_lock_irq(&queue->list_lock);
555 list_for_each_entry(block, &queue->outgoing, head)
556 data_available += block->size;
557 spin_unlock_irq(&queue->list_lock);
558 mutex_unlock(&queue->lock);
559
560 return data_available;
561}
562EXPORT_SYMBOL_GPL(iio_dma_buffer_data_available);
563
564/**
565 * iio_dma_buffer_set_bytes_per_datum() - DMA buffer set_bytes_per_datum callback
566 * @buffer: Buffer to set the bytes-per-datum for
567 * @bpd: The new bytes-per-datum value
568 *
569 * Should be used as the set_bytes_per_datum callback for iio_buffer_access_ops
570 * struct for DMA buffers.
571 */
572int iio_dma_buffer_set_bytes_per_datum(struct iio_buffer *buffer, size_t bpd)
573{
574 buffer->bytes_per_datum = bpd;
575
576 return 0;
577}
578EXPORT_SYMBOL_GPL(iio_dma_buffer_set_bytes_per_datum);
579
580/**
581 * iio_dma_buffer_set_length - DMA buffer set_length callback
582 * @buffer: Buffer to set the length for
583 * @length: The new buffer length
584 *
585 * Should be used as the set_length callback for iio_buffer_access_ops
586 * struct for DMA buffers.
587 */
588int iio_dma_buffer_set_length(struct iio_buffer *buffer, unsigned int length)
589{
590 /* Avoid an invalid state */
591 if (length < 2)
592 length = 2;
593 buffer->length = length;
594 buffer->watermark = length / 2;
595
596 return 0;
597}
598EXPORT_SYMBOL_GPL(iio_dma_buffer_set_length);
599
600/**
601 * iio_dma_buffer_init() - Initialize DMA buffer queue
602 * @queue: Buffer to initialize
603 * @dev: DMA device
604 * @ops: DMA buffer queue callback operations
605 *
606 * The DMA device will be used by the queue to do DMA memory allocations. So it
607 * should refer to the device that will perform the DMA to ensure that
608 * allocations are done from a memory region that can be accessed by the device.
609 */
610int iio_dma_buffer_init(struct iio_dma_buffer_queue *queue,
611 struct device *dev, const struct iio_dma_buffer_ops *ops)
612{
613 iio_buffer_init(&queue->buffer);
614 queue->buffer.length = PAGE_SIZE;
615 queue->buffer.watermark = queue->buffer.length / 2;
616 queue->dev = dev;
617 queue->ops = ops;
618
619 INIT_LIST_HEAD(&queue->incoming);
620 INIT_LIST_HEAD(&queue->outgoing);
621
622 mutex_init(&queue->lock);
623 spin_lock_init(&queue->list_lock);
624
625 return 0;
626}
627EXPORT_SYMBOL_GPL(iio_dma_buffer_init);
628
629/**
630 * iio_dma_buffer_exit() - Cleanup DMA buffer queue
631 * @queue: Buffer to cleanup
632 *
633 * After this function has completed it is safe to free any resources that are
634 * associated with the buffer and are accessed inside the callback operations.
635 */
636void iio_dma_buffer_exit(struct iio_dma_buffer_queue *queue)
637{
638 unsigned int i;
639
640 mutex_lock(&queue->lock);
641
642 spin_lock_irq(&queue->list_lock);
643 for (i = 0; i < ARRAY_SIZE(queue->fileio.blocks); i++) {
644 if (!queue->fileio.blocks[i])
645 continue;
646 queue->fileio.blocks[i]->state = IIO_BLOCK_STATE_DEAD;
647 }
648 INIT_LIST_HEAD(&queue->outgoing);
649 spin_unlock_irq(&queue->list_lock);
650
651 INIT_LIST_HEAD(&queue->incoming);
652
653 for (i = 0; i < ARRAY_SIZE(queue->fileio.blocks); i++) {
654 if (!queue->fileio.blocks[i])
655 continue;
656 iio_buffer_block_put(queue->fileio.blocks[i]);
657 queue->fileio.blocks[i] = NULL;
658 }
659 queue->fileio.active_block = NULL;
660 queue->ops = NULL;
661
662 mutex_unlock(&queue->lock);
663}
664EXPORT_SYMBOL_GPL(iio_dma_buffer_exit);
665
666/**
667 * iio_dma_buffer_release() - Release final buffer resources
668 * @queue: Buffer to release
669 *
670 * Frees resources that can't yet be freed in iio_dma_buffer_exit(). Should be
671 * called in the buffers release callback implementation right before freeing
672 * the memory associated with the buffer.
673 */
674void iio_dma_buffer_release(struct iio_dma_buffer_queue *queue)
675{
676 mutex_destroy(&queue->lock);
677}
678EXPORT_SYMBOL_GPL(iio_dma_buffer_release);
679
680MODULE_AUTHOR("Lars-Peter Clausen <lars@metafoo.de>");
681MODULE_DESCRIPTION("DMA buffer for the IIO framework");
682MODULE_LICENSE("GPL v2");
1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Copyright 2013-2015 Analog Devices Inc.
4 * Author: Lars-Peter Clausen <lars@metafoo.de>
5 */
6
7#include <linux/slab.h>
8#include <linux/kernel.h>
9#include <linux/module.h>
10#include <linux/device.h>
11#include <linux/workqueue.h>
12#include <linux/mutex.h>
13#include <linux/sched.h>
14#include <linux/poll.h>
15#include <linux/iio/buffer_impl.h>
16#include <linux/iio/buffer-dma.h>
17#include <linux/dma-mapping.h>
18#include <linux/sizes.h>
19
20/*
21 * For DMA buffers the storage is sub-divided into so called blocks. Each block
22 * has its own memory buffer. The size of the block is the granularity at which
23 * memory is exchanged between the hardware and the application. Increasing the
24 * basic unit of data exchange from one sample to one block decreases the
25 * management overhead that is associated with each sample. E.g. if we say the
26 * management overhead for one exchange is x and the unit of exchange is one
27 * sample the overhead will be x for each sample. Whereas when using a block
28 * which contains n samples the overhead per sample is reduced to x/n. This
29 * allows to achieve much higher samplerates than what can be sustained with
30 * the one sample approach.
31 *
32 * Blocks are exchanged between the DMA controller and the application via the
33 * means of two queues. The incoming queue and the outgoing queue. Blocks on the
34 * incoming queue are waiting for the DMA controller to pick them up and fill
35 * them with data. Block on the outgoing queue have been filled with data and
36 * are waiting for the application to dequeue them and read the data.
37 *
38 * A block can be in one of the following states:
39 * * Owned by the application. In this state the application can read data from
40 * the block.
41 * * On the incoming list: Blocks on the incoming list are queued up to be
42 * processed by the DMA controller.
43 * * Owned by the DMA controller: The DMA controller is processing the block
44 * and filling it with data.
45 * * On the outgoing list: Blocks on the outgoing list have been successfully
46 * processed by the DMA controller and contain data. They can be dequeued by
47 * the application.
48 * * Dead: A block that is dead has been marked as to be freed. It might still
49 * be owned by either the application or the DMA controller at the moment.
50 * But once they are done processing it instead of going to either the
51 * incoming or outgoing queue the block will be freed.
52 *
53 * In addition to this blocks are reference counted and the memory associated
54 * with both the block structure as well as the storage memory for the block
55 * will be freed when the last reference to the block is dropped. This means a
56 * block must not be accessed without holding a reference.
57 *
58 * The iio_dma_buffer implementation provides a generic infrastructure for
59 * managing the blocks.
60 *
61 * A driver for a specific piece of hardware that has DMA capabilities need to
62 * implement the submit() callback from the iio_dma_buffer_ops structure. This
63 * callback is supposed to initiate the DMA transfer copying data from the
64 * converter to the memory region of the block. Once the DMA transfer has been
65 * completed the driver must call iio_dma_buffer_block_done() for the completed
66 * block.
67 *
68 * Prior to this it must set the bytes_used field of the block contains
69 * the actual number of bytes in the buffer. Typically this will be equal to the
70 * size of the block, but if the DMA hardware has certain alignment requirements
71 * for the transfer length it might choose to use less than the full size. In
72 * either case it is expected that bytes_used is a multiple of the bytes per
73 * datum, i.e. the block must not contain partial samples.
74 *
75 * The driver must call iio_dma_buffer_block_done() for each block it has
76 * received through its submit_block() callback, even if it does not actually
77 * perform a DMA transfer for the block, e.g. because the buffer was disabled
78 * before the block transfer was started. In this case it should set bytes_used
79 * to 0.
80 *
81 * In addition it is recommended that a driver implements the abort() callback.
82 * It will be called when the buffer is disabled and can be used to cancel
83 * pending and stop active transfers.
84 *
85 * The specific driver implementation should use the default callback
86 * implementations provided by this module for the iio_buffer_access_funcs
87 * struct. It may overload some callbacks with custom variants if the hardware
88 * has special requirements that are not handled by the generic functions. If a
89 * driver chooses to overload a callback it has to ensure that the generic
90 * callback is called from within the custom callback.
91 */
92
93static void iio_buffer_block_release(struct kref *kref)
94{
95 struct iio_dma_buffer_block *block = container_of(kref,
96 struct iio_dma_buffer_block, kref);
97
98 WARN_ON(block->state != IIO_BLOCK_STATE_DEAD);
99
100 dma_free_coherent(block->queue->dev, PAGE_ALIGN(block->size),
101 block->vaddr, block->phys_addr);
102
103 iio_buffer_put(&block->queue->buffer);
104 kfree(block);
105}
106
107static void iio_buffer_block_get(struct iio_dma_buffer_block *block)
108{
109 kref_get(&block->kref);
110}
111
112static void iio_buffer_block_put(struct iio_dma_buffer_block *block)
113{
114 kref_put(&block->kref, iio_buffer_block_release);
115}
116
117/*
118 * dma_free_coherent can sleep, hence we need to take some special care to be
119 * able to drop a reference from an atomic context.
120 */
121static LIST_HEAD(iio_dma_buffer_dead_blocks);
122static DEFINE_SPINLOCK(iio_dma_buffer_dead_blocks_lock);
123
124static void iio_dma_buffer_cleanup_worker(struct work_struct *work)
125{
126 struct iio_dma_buffer_block *block, *_block;
127 LIST_HEAD(block_list);
128
129 spin_lock_irq(&iio_dma_buffer_dead_blocks_lock);
130 list_splice_tail_init(&iio_dma_buffer_dead_blocks, &block_list);
131 spin_unlock_irq(&iio_dma_buffer_dead_blocks_lock);
132
133 list_for_each_entry_safe(block, _block, &block_list, head)
134 iio_buffer_block_release(&block->kref);
135}
136static DECLARE_WORK(iio_dma_buffer_cleanup_work, iio_dma_buffer_cleanup_worker);
137
138static void iio_buffer_block_release_atomic(struct kref *kref)
139{
140 struct iio_dma_buffer_block *block;
141 unsigned long flags;
142
143 block = container_of(kref, struct iio_dma_buffer_block, kref);
144
145 spin_lock_irqsave(&iio_dma_buffer_dead_blocks_lock, flags);
146 list_add_tail(&block->head, &iio_dma_buffer_dead_blocks);
147 spin_unlock_irqrestore(&iio_dma_buffer_dead_blocks_lock, flags);
148
149 schedule_work(&iio_dma_buffer_cleanup_work);
150}
151
152/*
153 * Version of iio_buffer_block_put() that can be called from atomic context
154 */
155static void iio_buffer_block_put_atomic(struct iio_dma_buffer_block *block)
156{
157 kref_put(&block->kref, iio_buffer_block_release_atomic);
158}
159
160static struct iio_dma_buffer_queue *iio_buffer_to_queue(struct iio_buffer *buf)
161{
162 return container_of(buf, struct iio_dma_buffer_queue, buffer);
163}
164
165static struct iio_dma_buffer_block *iio_dma_buffer_alloc_block(
166 struct iio_dma_buffer_queue *queue, size_t size)
167{
168 struct iio_dma_buffer_block *block;
169
170 block = kzalloc(sizeof(*block), GFP_KERNEL);
171 if (!block)
172 return NULL;
173
174 block->vaddr = dma_alloc_coherent(queue->dev, PAGE_ALIGN(size),
175 &block->phys_addr, GFP_KERNEL);
176 if (!block->vaddr) {
177 kfree(block);
178 return NULL;
179 }
180
181 block->size = size;
182 block->state = IIO_BLOCK_STATE_DONE;
183 block->queue = queue;
184 INIT_LIST_HEAD(&block->head);
185 kref_init(&block->kref);
186
187 iio_buffer_get(&queue->buffer);
188
189 return block;
190}
191
192static void _iio_dma_buffer_block_done(struct iio_dma_buffer_block *block)
193{
194 if (block->state != IIO_BLOCK_STATE_DEAD)
195 block->state = IIO_BLOCK_STATE_DONE;
196}
197
198/**
199 * iio_dma_buffer_block_done() - Indicate that a block has been completed
200 * @block: The completed block
201 *
202 * Should be called when the DMA controller has finished handling the block to
203 * pass back ownership of the block to the queue.
204 */
205void iio_dma_buffer_block_done(struct iio_dma_buffer_block *block)
206{
207 struct iio_dma_buffer_queue *queue = block->queue;
208 unsigned long flags;
209
210 spin_lock_irqsave(&queue->list_lock, flags);
211 _iio_dma_buffer_block_done(block);
212 spin_unlock_irqrestore(&queue->list_lock, flags);
213
214 iio_buffer_block_put_atomic(block);
215 wake_up_interruptible_poll(&queue->buffer.pollq, EPOLLIN | EPOLLRDNORM);
216}
217EXPORT_SYMBOL_GPL(iio_dma_buffer_block_done);
218
219/**
220 * iio_dma_buffer_block_list_abort() - Indicate that a list block has been
221 * aborted
222 * @queue: Queue for which to complete blocks.
223 * @list: List of aborted blocks. All blocks in this list must be from @queue.
224 *
225 * Typically called from the abort() callback after the DMA controller has been
226 * stopped. This will set bytes_used to 0 for each block in the list and then
227 * hand the blocks back to the queue.
228 */
229void iio_dma_buffer_block_list_abort(struct iio_dma_buffer_queue *queue,
230 struct list_head *list)
231{
232 struct iio_dma_buffer_block *block, *_block;
233 unsigned long flags;
234
235 spin_lock_irqsave(&queue->list_lock, flags);
236 list_for_each_entry_safe(block, _block, list, head) {
237 list_del(&block->head);
238 block->bytes_used = 0;
239 _iio_dma_buffer_block_done(block);
240 iio_buffer_block_put_atomic(block);
241 }
242 spin_unlock_irqrestore(&queue->list_lock, flags);
243
244 wake_up_interruptible_poll(&queue->buffer.pollq, EPOLLIN | EPOLLRDNORM);
245}
246EXPORT_SYMBOL_GPL(iio_dma_buffer_block_list_abort);
247
248static bool iio_dma_block_reusable(struct iio_dma_buffer_block *block)
249{
250 /*
251 * If the core owns the block it can be re-used. This should be the
252 * default case when enabling the buffer, unless the DMA controller does
253 * not support abort and has not given back the block yet.
254 */
255 switch (block->state) {
256 case IIO_BLOCK_STATE_QUEUED:
257 case IIO_BLOCK_STATE_DONE:
258 return true;
259 default:
260 return false;
261 }
262}
263
264/**
265 * iio_dma_buffer_request_update() - DMA buffer request_update callback
266 * @buffer: The buffer which to request an update
267 *
268 * Should be used as the iio_dma_buffer_request_update() callback for
269 * iio_buffer_access_ops struct for DMA buffers.
270 */
271int iio_dma_buffer_request_update(struct iio_buffer *buffer)
272{
273 struct iio_dma_buffer_queue *queue = iio_buffer_to_queue(buffer);
274 struct iio_dma_buffer_block *block;
275 bool try_reuse = false;
276 size_t size;
277 int ret = 0;
278 int i;
279
280 /*
281 * Split the buffer into two even parts. This is used as a double
282 * buffering scheme with usually one block at a time being used by the
283 * DMA and the other one by the application.
284 */
285 size = DIV_ROUND_UP(queue->buffer.bytes_per_datum *
286 queue->buffer.length, 2);
287
288 mutex_lock(&queue->lock);
289
290 /* Allocations are page aligned */
291 if (PAGE_ALIGN(queue->fileio.block_size) == PAGE_ALIGN(size))
292 try_reuse = true;
293
294 queue->fileio.block_size = size;
295 queue->fileio.active_block = NULL;
296
297 spin_lock_irq(&queue->list_lock);
298 for (i = 0; i < ARRAY_SIZE(queue->fileio.blocks); i++) {
299 block = queue->fileio.blocks[i];
300
301 /* If we can't re-use it free it */
302 if (block && (!iio_dma_block_reusable(block) || !try_reuse))
303 block->state = IIO_BLOCK_STATE_DEAD;
304 }
305
306 /*
307 * At this point all blocks are either owned by the core or marked as
308 * dead. This means we can reset the lists without having to fear
309 * corrution.
310 */
311 spin_unlock_irq(&queue->list_lock);
312
313 INIT_LIST_HEAD(&queue->incoming);
314
315 for (i = 0; i < ARRAY_SIZE(queue->fileio.blocks); i++) {
316 if (queue->fileio.blocks[i]) {
317 block = queue->fileio.blocks[i];
318 if (block->state == IIO_BLOCK_STATE_DEAD) {
319 /* Could not reuse it */
320 iio_buffer_block_put(block);
321 block = NULL;
322 } else {
323 block->size = size;
324 }
325 } else {
326 block = NULL;
327 }
328
329 if (!block) {
330 block = iio_dma_buffer_alloc_block(queue, size);
331 if (!block) {
332 ret = -ENOMEM;
333 goto out_unlock;
334 }
335 queue->fileio.blocks[i] = block;
336 }
337
338 block->state = IIO_BLOCK_STATE_QUEUED;
339 list_add_tail(&block->head, &queue->incoming);
340 }
341
342out_unlock:
343 mutex_unlock(&queue->lock);
344
345 return ret;
346}
347EXPORT_SYMBOL_GPL(iio_dma_buffer_request_update);
348
349static void iio_dma_buffer_fileio_free(struct iio_dma_buffer_queue *queue)
350{
351 unsigned int i;
352
353 spin_lock_irq(&queue->list_lock);
354 for (i = 0; i < ARRAY_SIZE(queue->fileio.blocks); i++) {
355 if (!queue->fileio.blocks[i])
356 continue;
357 queue->fileio.blocks[i]->state = IIO_BLOCK_STATE_DEAD;
358 }
359 spin_unlock_irq(&queue->list_lock);
360
361 INIT_LIST_HEAD(&queue->incoming);
362
363 for (i = 0; i < ARRAY_SIZE(queue->fileio.blocks); i++) {
364 if (!queue->fileio.blocks[i])
365 continue;
366 iio_buffer_block_put(queue->fileio.blocks[i]);
367 queue->fileio.blocks[i] = NULL;
368 }
369 queue->fileio.active_block = NULL;
370}
371
372static void iio_dma_buffer_submit_block(struct iio_dma_buffer_queue *queue,
373 struct iio_dma_buffer_block *block)
374{
375 int ret;
376
377 /*
378 * If the hardware has already been removed we put the block into
379 * limbo. It will neither be on the incoming nor outgoing list, nor will
380 * it ever complete. It will just wait to be freed eventually.
381 */
382 if (!queue->ops)
383 return;
384
385 block->state = IIO_BLOCK_STATE_ACTIVE;
386 iio_buffer_block_get(block);
387 ret = queue->ops->submit(queue, block);
388 if (ret) {
389 /*
390 * This is a bit of a problem and there is not much we can do
391 * other then wait for the buffer to be disabled and re-enabled
392 * and try again. But it should not really happen unless we run
393 * out of memory or something similar.
394 *
395 * TODO: Implement support in the IIO core to allow buffers to
396 * notify consumers that something went wrong and the buffer
397 * should be disabled.
398 */
399 iio_buffer_block_put(block);
400 }
401}
402
403/**
404 * iio_dma_buffer_enable() - Enable DMA buffer
405 * @buffer: IIO buffer to enable
406 * @indio_dev: IIO device the buffer is attached to
407 *
408 * Needs to be called when the device that the buffer is attached to starts
409 * sampling. Typically should be the iio_buffer_access_ops enable callback.
410 *
411 * This will allocate the DMA buffers and start the DMA transfers.
412 */
413int iio_dma_buffer_enable(struct iio_buffer *buffer,
414 struct iio_dev *indio_dev)
415{
416 struct iio_dma_buffer_queue *queue = iio_buffer_to_queue(buffer);
417 struct iio_dma_buffer_block *block, *_block;
418
419 mutex_lock(&queue->lock);
420 queue->active = true;
421 list_for_each_entry_safe(block, _block, &queue->incoming, head) {
422 list_del(&block->head);
423 iio_dma_buffer_submit_block(queue, block);
424 }
425 mutex_unlock(&queue->lock);
426
427 return 0;
428}
429EXPORT_SYMBOL_GPL(iio_dma_buffer_enable);
430
431/**
432 * iio_dma_buffer_disable() - Disable DMA buffer
433 * @buffer: IIO DMA buffer to disable
434 * @indio_dev: IIO device the buffer is attached to
435 *
436 * Needs to be called when the device that the buffer is attached to stops
437 * sampling. Typically should be the iio_buffer_access_ops disable callback.
438 */
439int iio_dma_buffer_disable(struct iio_buffer *buffer,
440 struct iio_dev *indio_dev)
441{
442 struct iio_dma_buffer_queue *queue = iio_buffer_to_queue(buffer);
443
444 mutex_lock(&queue->lock);
445 queue->active = false;
446
447 if (queue->ops && queue->ops->abort)
448 queue->ops->abort(queue);
449 mutex_unlock(&queue->lock);
450
451 return 0;
452}
453EXPORT_SYMBOL_GPL(iio_dma_buffer_disable);
454
455static void iio_dma_buffer_enqueue(struct iio_dma_buffer_queue *queue,
456 struct iio_dma_buffer_block *block)
457{
458 if (block->state == IIO_BLOCK_STATE_DEAD) {
459 iio_buffer_block_put(block);
460 } else if (queue->active) {
461 iio_dma_buffer_submit_block(queue, block);
462 } else {
463 block->state = IIO_BLOCK_STATE_QUEUED;
464 list_add_tail(&block->head, &queue->incoming);
465 }
466}
467
468static struct iio_dma_buffer_block *iio_dma_buffer_dequeue(
469 struct iio_dma_buffer_queue *queue)
470{
471 struct iio_dma_buffer_block *block;
472 unsigned int idx;
473
474 spin_lock_irq(&queue->list_lock);
475
476 idx = queue->fileio.next_dequeue;
477 block = queue->fileio.blocks[idx];
478
479 if (block->state == IIO_BLOCK_STATE_DONE) {
480 idx = (idx + 1) % ARRAY_SIZE(queue->fileio.blocks);
481 queue->fileio.next_dequeue = idx;
482 } else {
483 block = NULL;
484 }
485
486 spin_unlock_irq(&queue->list_lock);
487
488 return block;
489}
490
491/**
492 * iio_dma_buffer_read() - DMA buffer read callback
493 * @buffer: Buffer to read form
494 * @n: Number of bytes to read
495 * @user_buffer: Userspace buffer to copy the data to
496 *
497 * Should be used as the read callback for iio_buffer_access_ops
498 * struct for DMA buffers.
499 */
500int iio_dma_buffer_read(struct iio_buffer *buffer, size_t n,
501 char __user *user_buffer)
502{
503 struct iio_dma_buffer_queue *queue = iio_buffer_to_queue(buffer);
504 struct iio_dma_buffer_block *block;
505 int ret;
506
507 if (n < buffer->bytes_per_datum)
508 return -EINVAL;
509
510 mutex_lock(&queue->lock);
511
512 if (!queue->fileio.active_block) {
513 block = iio_dma_buffer_dequeue(queue);
514 if (block == NULL) {
515 ret = 0;
516 goto out_unlock;
517 }
518 queue->fileio.pos = 0;
519 queue->fileio.active_block = block;
520 } else {
521 block = queue->fileio.active_block;
522 }
523
524 n = rounddown(n, buffer->bytes_per_datum);
525 if (n > block->bytes_used - queue->fileio.pos)
526 n = block->bytes_used - queue->fileio.pos;
527
528 if (copy_to_user(user_buffer, block->vaddr + queue->fileio.pos, n)) {
529 ret = -EFAULT;
530 goto out_unlock;
531 }
532
533 queue->fileio.pos += n;
534
535 if (queue->fileio.pos == block->bytes_used) {
536 queue->fileio.active_block = NULL;
537 iio_dma_buffer_enqueue(queue, block);
538 }
539
540 ret = n;
541
542out_unlock:
543 mutex_unlock(&queue->lock);
544
545 return ret;
546}
547EXPORT_SYMBOL_GPL(iio_dma_buffer_read);
548
549/**
550 * iio_dma_buffer_data_available() - DMA buffer data_available callback
551 * @buf: Buffer to check for data availability
552 *
553 * Should be used as the data_available callback for iio_buffer_access_ops
554 * struct for DMA buffers.
555 */
556size_t iio_dma_buffer_data_available(struct iio_buffer *buf)
557{
558 struct iio_dma_buffer_queue *queue = iio_buffer_to_queue(buf);
559 struct iio_dma_buffer_block *block;
560 size_t data_available = 0;
561 unsigned int i;
562
563 /*
564 * For counting the available bytes we'll use the size of the block not
565 * the number of actual bytes available in the block. Otherwise it is
566 * possible that we end up with a value that is lower than the watermark
567 * but won't increase since all blocks are in use.
568 */
569
570 mutex_lock(&queue->lock);
571 if (queue->fileio.active_block)
572 data_available += queue->fileio.active_block->size;
573
574 spin_lock_irq(&queue->list_lock);
575
576 for (i = 0; i < ARRAY_SIZE(queue->fileio.blocks); i++) {
577 block = queue->fileio.blocks[i];
578
579 if (block != queue->fileio.active_block
580 && block->state == IIO_BLOCK_STATE_DONE)
581 data_available += block->size;
582 }
583
584 spin_unlock_irq(&queue->list_lock);
585 mutex_unlock(&queue->lock);
586
587 return data_available;
588}
589EXPORT_SYMBOL_GPL(iio_dma_buffer_data_available);
590
591/**
592 * iio_dma_buffer_set_bytes_per_datum() - DMA buffer set_bytes_per_datum callback
593 * @buffer: Buffer to set the bytes-per-datum for
594 * @bpd: The new bytes-per-datum value
595 *
596 * Should be used as the set_bytes_per_datum callback for iio_buffer_access_ops
597 * struct for DMA buffers.
598 */
599int iio_dma_buffer_set_bytes_per_datum(struct iio_buffer *buffer, size_t bpd)
600{
601 buffer->bytes_per_datum = bpd;
602
603 return 0;
604}
605EXPORT_SYMBOL_GPL(iio_dma_buffer_set_bytes_per_datum);
606
607/**
608 * iio_dma_buffer_set_length - DMA buffer set_length callback
609 * @buffer: Buffer to set the length for
610 * @length: The new buffer length
611 *
612 * Should be used as the set_length callback for iio_buffer_access_ops
613 * struct for DMA buffers.
614 */
615int iio_dma_buffer_set_length(struct iio_buffer *buffer, unsigned int length)
616{
617 /* Avoid an invalid state */
618 if (length < 2)
619 length = 2;
620 buffer->length = length;
621 buffer->watermark = length / 2;
622
623 return 0;
624}
625EXPORT_SYMBOL_GPL(iio_dma_buffer_set_length);
626
627/**
628 * iio_dma_buffer_init() - Initialize DMA buffer queue
629 * @queue: Buffer to initialize
630 * @dev: DMA device
631 * @ops: DMA buffer queue callback operations
632 *
633 * The DMA device will be used by the queue to do DMA memory allocations. So it
634 * should refer to the device that will perform the DMA to ensure that
635 * allocations are done from a memory region that can be accessed by the device.
636 */
637int iio_dma_buffer_init(struct iio_dma_buffer_queue *queue,
638 struct device *dev, const struct iio_dma_buffer_ops *ops)
639{
640 iio_buffer_init(&queue->buffer);
641 queue->buffer.length = PAGE_SIZE;
642 queue->buffer.watermark = queue->buffer.length / 2;
643 queue->dev = dev;
644 queue->ops = ops;
645
646 INIT_LIST_HEAD(&queue->incoming);
647
648 mutex_init(&queue->lock);
649 spin_lock_init(&queue->list_lock);
650
651 return 0;
652}
653EXPORT_SYMBOL_GPL(iio_dma_buffer_init);
654
655/**
656 * iio_dma_buffer_exit() - Cleanup DMA buffer queue
657 * @queue: Buffer to cleanup
658 *
659 * After this function has completed it is safe to free any resources that are
660 * associated with the buffer and are accessed inside the callback operations.
661 */
662void iio_dma_buffer_exit(struct iio_dma_buffer_queue *queue)
663{
664 mutex_lock(&queue->lock);
665
666 iio_dma_buffer_fileio_free(queue);
667 queue->ops = NULL;
668
669 mutex_unlock(&queue->lock);
670}
671EXPORT_SYMBOL_GPL(iio_dma_buffer_exit);
672
673/**
674 * iio_dma_buffer_release() - Release final buffer resources
675 * @queue: Buffer to release
676 *
677 * Frees resources that can't yet be freed in iio_dma_buffer_exit(). Should be
678 * called in the buffers release callback implementation right before freeing
679 * the memory associated with the buffer.
680 */
681void iio_dma_buffer_release(struct iio_dma_buffer_queue *queue)
682{
683 mutex_destroy(&queue->lock);
684}
685EXPORT_SYMBOL_GPL(iio_dma_buffer_release);
686
687MODULE_AUTHOR("Lars-Peter Clausen <lars@metafoo.de>");
688MODULE_DESCRIPTION("DMA buffer for the IIO framework");
689MODULE_LICENSE("GPL v2");