1 // SPDX-License-Identifier: GPL-2.0+
2 /*
3  * comedi_buf.c
4  *
5  * COMEDI - Linux Control and Measurement Device Interface
6  * Copyright (C) 1997-2000 David A. Schleef <ds@schleef.org>
7  * Copyright (C) 2002 Frank Mori Hess <fmhess@users.sourceforge.net>
8  */
9 
10 #include <linux/vmalloc.h>
11 #include <linux/slab.h>
12 
13 #include "comedidev.h"
14 #include "comedi_internal.h"
15 
16 #ifdef PAGE_KERNEL_NOCACHE
17 #define COMEDI_PAGE_PROTECTION		PAGE_KERNEL_NOCACHE
18 #else
19 #define COMEDI_PAGE_PROTECTION		PAGE_KERNEL
20 #endif
21 
comedi_buf_map_kref_release(struct kref * kref)22 static void comedi_buf_map_kref_release(struct kref *kref)
23 {
24 	struct comedi_buf_map *bm =
25 		container_of(kref, struct comedi_buf_map, refcount);
26 	struct comedi_buf_page *buf;
27 	unsigned int i;
28 
29 	if (bm->page_list) {
30 		if (bm->dma_dir != DMA_NONE) {
31 			/*
32 			 * DMA buffer was allocated as a single block.
33 			 * Address is in page_list[0].
34 			 */
35 			buf = &bm->page_list[0];
36 			dma_free_coherent(bm->dma_hw_dev,
37 					  PAGE_SIZE * bm->n_pages,
38 					  buf->virt_addr, buf->dma_addr);
39 		} else {
40 			for (i = 0; i < bm->n_pages; i++) {
41 				buf = &bm->page_list[i];
42 				ClearPageReserved(virt_to_page(buf->virt_addr));
43 				free_page((unsigned long)buf->virt_addr);
44 			}
45 		}
46 		vfree(bm->page_list);
47 	}
48 	if (bm->dma_dir != DMA_NONE)
49 		put_device(bm->dma_hw_dev);
50 	kfree(bm);
51 }
52 
__comedi_buf_free(struct comedi_device * dev,struct comedi_subdevice * s)53 static void __comedi_buf_free(struct comedi_device *dev,
54 			      struct comedi_subdevice *s)
55 {
56 	struct comedi_async *async = s->async;
57 	struct comedi_buf_map *bm;
58 	unsigned long flags;
59 
60 	if (async->prealloc_buf) {
61 		if (s->async_dma_dir == DMA_NONE)
62 			vunmap(async->prealloc_buf);
63 		async->prealloc_buf = NULL;
64 		async->prealloc_bufsz = 0;
65 	}
66 
67 	spin_lock_irqsave(&s->spin_lock, flags);
68 	bm = async->buf_map;
69 	async->buf_map = NULL;
70 	spin_unlock_irqrestore(&s->spin_lock, flags);
71 	comedi_buf_map_put(bm);
72 }
73 
74 static struct comedi_buf_map *
comedi_buf_map_alloc(struct comedi_device * dev,enum dma_data_direction dma_dir,unsigned int n_pages)75 comedi_buf_map_alloc(struct comedi_device *dev, enum dma_data_direction dma_dir,
76 		     unsigned int n_pages)
77 {
78 	struct comedi_buf_map *bm;
79 	struct comedi_buf_page *buf;
80 	unsigned int i;
81 
82 	bm = kzalloc(sizeof(*bm), GFP_KERNEL);
83 	if (!bm)
84 		return NULL;
85 
86 	kref_init(&bm->refcount);
87 	bm->dma_dir = dma_dir;
88 	if (bm->dma_dir != DMA_NONE) {
89 		/* Need ref to hardware device to free buffer later. */
90 		bm->dma_hw_dev = get_device(dev->hw_dev);
91 	}
92 
93 	bm->page_list = vzalloc(sizeof(*buf) * n_pages);
94 	if (!bm->page_list)
95 		goto err;
96 
97 	if (bm->dma_dir != DMA_NONE) {
98 		void *virt_addr;
99 		dma_addr_t dma_addr;
100 
101 		/*
102 		 * Currently, the DMA buffer needs to be allocated as a
103 		 * single block so that it can be mmap()'ed.
104 		 */
105 		virt_addr = dma_alloc_coherent(bm->dma_hw_dev,
106 					       PAGE_SIZE * n_pages, &dma_addr,
107 					       GFP_KERNEL);
108 		if (!virt_addr)
109 			goto err;
110 
111 		for (i = 0; i < n_pages; i++) {
112 			buf = &bm->page_list[i];
113 			buf->virt_addr = virt_addr + (i << PAGE_SHIFT);
114 			buf->dma_addr = dma_addr + (i << PAGE_SHIFT);
115 		}
116 
117 		bm->n_pages = i;
118 	} else {
119 		for (i = 0; i < n_pages; i++) {
120 			buf = &bm->page_list[i];
121 			buf->virt_addr = (void *)get_zeroed_page(GFP_KERNEL);
122 			if (!buf->virt_addr)
123 				break;
124 
125 			SetPageReserved(virt_to_page(buf->virt_addr));
126 		}
127 
128 		bm->n_pages = i;
129 		if (i < n_pages)
130 			goto err;
131 	}
132 
133 	return bm;
134 
135 err:
136 	comedi_buf_map_put(bm);
137 	return NULL;
138 }
139 
__comedi_buf_alloc(struct comedi_device * dev,struct comedi_subdevice * s,unsigned int n_pages)140 static void __comedi_buf_alloc(struct comedi_device *dev,
141 			       struct comedi_subdevice *s,
142 			       unsigned int n_pages)
143 {
144 	struct comedi_async *async = s->async;
145 	struct page **pages = NULL;
146 	struct comedi_buf_map *bm;
147 	struct comedi_buf_page *buf;
148 	unsigned long flags;
149 	unsigned int i;
150 
151 	if (!IS_ENABLED(CONFIG_HAS_DMA) && s->async_dma_dir != DMA_NONE) {
152 		dev_err(dev->class_dev,
153 			"dma buffer allocation not supported\n");
154 		return;
155 	}
156 
157 	bm = comedi_buf_map_alloc(dev, s->async_dma_dir, n_pages);
158 	if (!bm)
159 		return;
160 
161 	spin_lock_irqsave(&s->spin_lock, flags);
162 	async->buf_map = bm;
163 	spin_unlock_irqrestore(&s->spin_lock, flags);
164 
165 	if (bm->dma_dir != DMA_NONE) {
166 		/*
167 		 * DMA buffer was allocated as a single block.
168 		 * Address is in page_list[0].
169 		 */
170 		buf = &bm->page_list[0];
171 		async->prealloc_buf = buf->virt_addr;
172 	} else {
173 		pages = vmalloc(sizeof(struct page *) * n_pages);
174 		if (!pages)
175 			return;
176 
177 		for (i = 0; i < n_pages; i++) {
178 			buf = &bm->page_list[i];
179 			pages[i] = virt_to_page(buf->virt_addr);
180 		}
181 
182 		/* vmap the pages to prealloc_buf */
183 		async->prealloc_buf = vmap(pages, n_pages, VM_MAP,
184 					   COMEDI_PAGE_PROTECTION);
185 
186 		vfree(pages);
187 	}
188 }
189 
comedi_buf_map_get(struct comedi_buf_map * bm)190 void comedi_buf_map_get(struct comedi_buf_map *bm)
191 {
192 	if (bm)
193 		kref_get(&bm->refcount);
194 }
195 
comedi_buf_map_put(struct comedi_buf_map * bm)196 int comedi_buf_map_put(struct comedi_buf_map *bm)
197 {
198 	if (bm)
199 		return kref_put(&bm->refcount, comedi_buf_map_kref_release);
200 	return 1;
201 }
202 
203 /* helper for "access" vm operation */
comedi_buf_map_access(struct comedi_buf_map * bm,unsigned long offset,void * buf,int len,int write)204 int comedi_buf_map_access(struct comedi_buf_map *bm, unsigned long offset,
205 			  void *buf, int len, int write)
206 {
207 	unsigned int pgoff = offset_in_page(offset);
208 	unsigned long pg = offset >> PAGE_SHIFT;
209 	int done = 0;
210 
211 	while (done < len && pg < bm->n_pages) {
212 		int l = min_t(int, len - done, PAGE_SIZE - pgoff);
213 		void *b = bm->page_list[pg].virt_addr + pgoff;
214 
215 		if (write)
216 			memcpy(b, buf, l);
217 		else
218 			memcpy(buf, b, l);
219 		buf += l;
220 		done += l;
221 		pg++;
222 		pgoff = 0;
223 	}
224 	return done;
225 }
226 
227 /* returns s->async->buf_map and increments its kref refcount */
228 struct comedi_buf_map *
comedi_buf_map_from_subdev_get(struct comedi_subdevice * s)229 comedi_buf_map_from_subdev_get(struct comedi_subdevice *s)
230 {
231 	struct comedi_async *async = s->async;
232 	struct comedi_buf_map *bm = NULL;
233 	unsigned long flags;
234 
235 	if (!async)
236 		return NULL;
237 
238 	spin_lock_irqsave(&s->spin_lock, flags);
239 	bm = async->buf_map;
240 	/* only want it if buffer pages allocated */
241 	if (bm && bm->n_pages)
242 		comedi_buf_map_get(bm);
243 	else
244 		bm = NULL;
245 	spin_unlock_irqrestore(&s->spin_lock, flags);
246 
247 	return bm;
248 }
249 
comedi_buf_is_mmapped(struct comedi_subdevice * s)250 bool comedi_buf_is_mmapped(struct comedi_subdevice *s)
251 {
252 	struct comedi_buf_map *bm = s->async->buf_map;
253 
254 	return bm && (kref_read(&bm->refcount) > 1);
255 }
256 
comedi_buf_alloc(struct comedi_device * dev,struct comedi_subdevice * s,unsigned long new_size)257 int comedi_buf_alloc(struct comedi_device *dev, struct comedi_subdevice *s,
258 		     unsigned long new_size)
259 {
260 	struct comedi_async *async = s->async;
261 
262 	lockdep_assert_held(&dev->mutex);
263 
264 	/* Round up new_size to multiple of PAGE_SIZE */
265 	new_size = (new_size + PAGE_SIZE - 1) & PAGE_MASK;
266 
267 	/* if no change is required, do nothing */
268 	if (async->prealloc_buf && async->prealloc_bufsz == new_size)
269 		return 0;
270 
271 	/* deallocate old buffer */
272 	__comedi_buf_free(dev, s);
273 
274 	/* allocate new buffer */
275 	if (new_size) {
276 		unsigned int n_pages = new_size >> PAGE_SHIFT;
277 
278 		__comedi_buf_alloc(dev, s, n_pages);
279 
280 		if (!async->prealloc_buf) {
281 			/* allocation failed */
282 			__comedi_buf_free(dev, s);
283 			return -ENOMEM;
284 		}
285 	}
286 	async->prealloc_bufsz = new_size;
287 
288 	return 0;
289 }
290 
comedi_buf_reset(struct comedi_subdevice * s)291 void comedi_buf_reset(struct comedi_subdevice *s)
292 {
293 	struct comedi_async *async = s->async;
294 
295 	async->buf_write_alloc_count = 0;
296 	async->buf_write_count = 0;
297 	async->buf_read_alloc_count = 0;
298 	async->buf_read_count = 0;
299 
300 	async->buf_write_ptr = 0;
301 	async->buf_read_ptr = 0;
302 
303 	async->cur_chan = 0;
304 	async->scans_done = 0;
305 	async->scan_progress = 0;
306 	async->munge_chan = 0;
307 	async->munge_count = 0;
308 	async->munge_ptr = 0;
309 
310 	async->events = 0;
311 }
312 
comedi_buf_write_n_unalloc(struct comedi_subdevice * s)313 static unsigned int comedi_buf_write_n_unalloc(struct comedi_subdevice *s)
314 {
315 	struct comedi_async *async = s->async;
316 	unsigned int free_end = async->buf_read_count + async->prealloc_bufsz;
317 
318 	return free_end - async->buf_write_alloc_count;
319 }
320 
comedi_buf_write_n_available(struct comedi_subdevice * s)321 unsigned int comedi_buf_write_n_available(struct comedi_subdevice *s)
322 {
323 	struct comedi_async *async = s->async;
324 	unsigned int free_end = async->buf_read_count + async->prealloc_bufsz;
325 
326 	return free_end - async->buf_write_count;
327 }
328 
329 /**
330  * comedi_buf_write_alloc() - Reserve buffer space for writing
331  * @s: COMEDI subdevice.
332  * @nbytes: Maximum space to reserve in bytes.
333  *
334  * Reserve up to @nbytes bytes of space to be written in the COMEDI acquisition
335  * data buffer associated with the subdevice.  The amount reserved is limited
336  * by the space available.
337  *
338  * Return: The amount of space reserved in bytes.
339  */
comedi_buf_write_alloc(struct comedi_subdevice * s,unsigned int nbytes)340 unsigned int comedi_buf_write_alloc(struct comedi_subdevice *s,
341 				    unsigned int nbytes)
342 {
343 	struct comedi_async *async = s->async;
344 	unsigned int unalloc = comedi_buf_write_n_unalloc(s);
345 
346 	if (nbytes > unalloc)
347 		nbytes = unalloc;
348 
349 	async->buf_write_alloc_count += nbytes;
350 
351 	/*
352 	 * ensure the async buffer 'counts' are read and updated
353 	 * before we write data to the write-alloc'ed buffer space
354 	 */
355 	smp_mb();
356 
357 	return nbytes;
358 }
359 EXPORT_SYMBOL_GPL(comedi_buf_write_alloc);
360 
361 /*
362  * munging is applied to data by core as it passes between user
363  * and kernel space
364  */
comedi_buf_munge(struct comedi_subdevice * s,unsigned int num_bytes)365 static unsigned int comedi_buf_munge(struct comedi_subdevice *s,
366 				     unsigned int num_bytes)
367 {
368 	struct comedi_async *async = s->async;
369 	unsigned int count = 0;
370 	const unsigned int num_sample_bytes = comedi_bytes_per_sample(s);
371 
372 	if (!s->munge || (async->cmd.flags & CMDF_RAWDATA)) {
373 		async->munge_count += num_bytes;
374 		return num_bytes;
375 	}
376 
377 	/* don't munge partial samples */
378 	num_bytes -= num_bytes % num_sample_bytes;
379 	while (count < num_bytes) {
380 		int block_size = num_bytes - count;
381 		unsigned int buf_end;
382 
383 		buf_end = async->prealloc_bufsz - async->munge_ptr;
384 		if (block_size > buf_end)
385 			block_size = buf_end;
386 
387 		s->munge(s->device, s,
388 			 async->prealloc_buf + async->munge_ptr,
389 			 block_size, async->munge_chan);
390 
391 		/*
392 		 * ensure data is munged in buffer before the
393 		 * async buffer munge_count is incremented
394 		 */
395 		smp_wmb();
396 
397 		async->munge_chan += block_size / num_sample_bytes;
398 		async->munge_chan %= async->cmd.chanlist_len;
399 		async->munge_count += block_size;
400 		async->munge_ptr += block_size;
401 		async->munge_ptr %= async->prealloc_bufsz;
402 		count += block_size;
403 	}
404 
405 	return count;
406 }
407 
comedi_buf_write_n_allocated(struct comedi_subdevice * s)408 unsigned int comedi_buf_write_n_allocated(struct comedi_subdevice *s)
409 {
410 	struct comedi_async *async = s->async;
411 
412 	return async->buf_write_alloc_count - async->buf_write_count;
413 }
414 
415 /**
416  * comedi_buf_write_free() - Free buffer space after it is written
417  * @s: COMEDI subdevice.
418  * @nbytes: Maximum space to free in bytes.
419  *
420  * Free up to @nbytes bytes of space previously reserved for writing in the
421  * COMEDI acquisition data buffer associated with the subdevice.  The amount of
422  * space freed is limited to the amount that was reserved.  The freed space is
423  * assumed to have been filled with sample data by the writer.
424  *
425  * If the samples in the freed space need to be "munged", do so here.  The
426  * freed space becomes available for allocation by the reader.
427  *
428  * Return: The amount of space freed in bytes.
429  */
comedi_buf_write_free(struct comedi_subdevice * s,unsigned int nbytes)430 unsigned int comedi_buf_write_free(struct comedi_subdevice *s,
431 				   unsigned int nbytes)
432 {
433 	struct comedi_async *async = s->async;
434 	unsigned int allocated = comedi_buf_write_n_allocated(s);
435 
436 	if (nbytes > allocated)
437 		nbytes = allocated;
438 
439 	async->buf_write_count += nbytes;
440 	async->buf_write_ptr += nbytes;
441 	comedi_buf_munge(s, async->buf_write_count - async->munge_count);
442 	if (async->buf_write_ptr >= async->prealloc_bufsz)
443 		async->buf_write_ptr %= async->prealloc_bufsz;
444 
445 	return nbytes;
446 }
447 EXPORT_SYMBOL_GPL(comedi_buf_write_free);
448 
449 /**
450  * comedi_buf_read_n_available() - Determine amount of readable buffer space
451  * @s: COMEDI subdevice.
452  *
453  * Determine the amount of readable buffer space in the COMEDI acquisition data
454  * buffer associated with the subdevice.  The readable buffer space is that
455  * which has been freed by the writer and "munged" to the sample data format
456  * expected by COMEDI if necessary.
457  *
458  * Return: The amount of readable buffer space.
459  */
comedi_buf_read_n_available(struct comedi_subdevice * s)460 unsigned int comedi_buf_read_n_available(struct comedi_subdevice *s)
461 {
462 	struct comedi_async *async = s->async;
463 	unsigned int num_bytes;
464 
465 	if (!async)
466 		return 0;
467 
468 	num_bytes = async->munge_count - async->buf_read_count;
469 
470 	/*
471 	 * ensure the async buffer 'counts' are read before we
472 	 * attempt to read data from the buffer
473 	 */
474 	smp_rmb();
475 
476 	return num_bytes;
477 }
478 EXPORT_SYMBOL_GPL(comedi_buf_read_n_available);
479 
480 /**
481  * comedi_buf_read_alloc() - Reserve buffer space for reading
482  * @s: COMEDI subdevice.
483  * @nbytes: Maximum space to reserve in bytes.
484  *
485  * Reserve up to @nbytes bytes of previously written and "munged" buffer space
486  * for reading in the COMEDI acquisition data buffer associated with the
487  * subdevice.  The amount reserved is limited to the space available.  The
488  * reader can read from the reserved space and then free it.  A reader is also
489  * allowed to read from the space before reserving it as long as it determines
490  * the amount of readable data available, but the space needs to be marked as
491  * reserved before it can be freed.
492  *
493  * Return: The amount of space reserved in bytes.
494  */
comedi_buf_read_alloc(struct comedi_subdevice * s,unsigned int nbytes)495 unsigned int comedi_buf_read_alloc(struct comedi_subdevice *s,
496 				   unsigned int nbytes)
497 {
498 	struct comedi_async *async = s->async;
499 	unsigned int available;
500 
501 	available = async->munge_count - async->buf_read_alloc_count;
502 	if (nbytes > available)
503 		nbytes = available;
504 
505 	async->buf_read_alloc_count += nbytes;
506 
507 	/*
508 	 * ensure the async buffer 'counts' are read before we
509 	 * attempt to read data from the read-alloc'ed buffer space
510 	 */
511 	smp_rmb();
512 
513 	return nbytes;
514 }
515 EXPORT_SYMBOL_GPL(comedi_buf_read_alloc);
516 
comedi_buf_read_n_allocated(struct comedi_async * async)517 static unsigned int comedi_buf_read_n_allocated(struct comedi_async *async)
518 {
519 	return async->buf_read_alloc_count - async->buf_read_count;
520 }
521 
522 /**
523  * comedi_buf_read_free() - Free buffer space after it has been read
524  * @s: COMEDI subdevice.
525  * @nbytes: Maximum space to free in bytes.
526  *
527  * Free up to @nbytes bytes of buffer space previously reserved for reading in
528  * the COMEDI acquisition data buffer associated with the subdevice.  The
529  * amount of space freed is limited to the amount that was reserved.
530  *
531  * The freed space becomes available for allocation by the writer.
532  *
533  * Return: The amount of space freed in bytes.
534  */
comedi_buf_read_free(struct comedi_subdevice * s,unsigned int nbytes)535 unsigned int comedi_buf_read_free(struct comedi_subdevice *s,
536 				  unsigned int nbytes)
537 {
538 	struct comedi_async *async = s->async;
539 	unsigned int allocated;
540 
541 	/*
542 	 * ensure data has been read out of buffer before
543 	 * the async read count is incremented
544 	 */
545 	smp_mb();
546 
547 	allocated = comedi_buf_read_n_allocated(async);
548 	if (nbytes > allocated)
549 		nbytes = allocated;
550 
551 	async->buf_read_count += nbytes;
552 	async->buf_read_ptr += nbytes;
553 	async->buf_read_ptr %= async->prealloc_bufsz;
554 	return nbytes;
555 }
556 EXPORT_SYMBOL_GPL(comedi_buf_read_free);
557 
comedi_buf_memcpy_to(struct comedi_subdevice * s,const void * data,unsigned int num_bytes)558 static void comedi_buf_memcpy_to(struct comedi_subdevice *s,
559 				 const void *data, unsigned int num_bytes)
560 {
561 	struct comedi_async *async = s->async;
562 	unsigned int write_ptr = async->buf_write_ptr;
563 
564 	while (num_bytes) {
565 		unsigned int block_size;
566 
567 		if (write_ptr + num_bytes > async->prealloc_bufsz)
568 			block_size = async->prealloc_bufsz - write_ptr;
569 		else
570 			block_size = num_bytes;
571 
572 		memcpy(async->prealloc_buf + write_ptr, data, block_size);
573 
574 		data += block_size;
575 		num_bytes -= block_size;
576 
577 		write_ptr = 0;
578 	}
579 }
580 
comedi_buf_memcpy_from(struct comedi_subdevice * s,void * dest,unsigned int nbytes)581 static void comedi_buf_memcpy_from(struct comedi_subdevice *s,
582 				   void *dest, unsigned int nbytes)
583 {
584 	void *src;
585 	struct comedi_async *async = s->async;
586 	unsigned int read_ptr = async->buf_read_ptr;
587 
588 	while (nbytes) {
589 		unsigned int block_size;
590 
591 		src = async->prealloc_buf + read_ptr;
592 
593 		if (nbytes >= async->prealloc_bufsz - read_ptr)
594 			block_size = async->prealloc_bufsz - read_ptr;
595 		else
596 			block_size = nbytes;
597 
598 		memcpy(dest, src, block_size);
599 		nbytes -= block_size;
600 		dest += block_size;
601 		read_ptr = 0;
602 	}
603 }
604 
605 /**
606  * comedi_buf_write_samples() - Write sample data to COMEDI buffer
607  * @s: COMEDI subdevice.
608  * @data: Pointer to source samples.
609  * @nsamples: Number of samples to write.
610  *
611  * Write up to @nsamples samples to the COMEDI acquisition data buffer
612  * associated with the subdevice, mark it as written and update the
613  * acquisition scan progress.  If there is not enough room for the specified
614  * number of samples, the number of samples written is limited to the number
615  * that will fit and the %COMEDI_CB_OVERFLOW event flag is set to cause the
616  * acquisition to terminate with an overrun error.  Set the %COMEDI_CB_BLOCK
617  * event flag if any samples are written to cause waiting tasks to be woken
618  * when the event flags are processed.
619  *
620  * Return: The amount of data written in bytes.
621  */
comedi_buf_write_samples(struct comedi_subdevice * s,const void * data,unsigned int nsamples)622 unsigned int comedi_buf_write_samples(struct comedi_subdevice *s,
623 				      const void *data, unsigned int nsamples)
624 {
625 	unsigned int max_samples;
626 	unsigned int nbytes;
627 
628 	/*
629 	 * Make sure there is enough room in the buffer for all the samples.
630 	 * If not, clamp the nsamples to the number that will fit, flag the
631 	 * buffer overrun and add the samples that fit.
632 	 */
633 	max_samples = comedi_bytes_to_samples(s, comedi_buf_write_n_unalloc(s));
634 	if (nsamples > max_samples) {
635 		dev_warn(s->device->class_dev, "buffer overrun\n");
636 		s->async->events |= COMEDI_CB_OVERFLOW;
637 		nsamples = max_samples;
638 	}
639 
640 	if (nsamples == 0)
641 		return 0;
642 
643 	nbytes = comedi_buf_write_alloc(s,
644 					comedi_samples_to_bytes(s, nsamples));
645 	comedi_buf_memcpy_to(s, data, nbytes);
646 	comedi_buf_write_free(s, nbytes);
647 	comedi_inc_scan_progress(s, nbytes);
648 	s->async->events |= COMEDI_CB_BLOCK;
649 
650 	return nbytes;
651 }
652 EXPORT_SYMBOL_GPL(comedi_buf_write_samples);
653 
654 /**
655  * comedi_buf_read_samples() - Read sample data from COMEDI buffer
656  * @s: COMEDI subdevice.
657  * @data: Pointer to destination.
658  * @nsamples: Maximum number of samples to read.
659  *
660  * Read up to @nsamples samples from the COMEDI acquisition data buffer
661  * associated with the subdevice, mark it as read and update the acquisition
662  * scan progress.  Limit the number of samples read to the number available.
663  * Set the %COMEDI_CB_BLOCK event flag if any samples are read to cause waiting
664  * tasks to be woken when the event flags are processed.
665  *
666  * Return: The amount of data read in bytes.
667  */
comedi_buf_read_samples(struct comedi_subdevice * s,void * data,unsigned int nsamples)668 unsigned int comedi_buf_read_samples(struct comedi_subdevice *s,
669 				     void *data, unsigned int nsamples)
670 {
671 	unsigned int max_samples;
672 	unsigned int nbytes;
673 
674 	/* clamp nsamples to the number of full samples available */
675 	max_samples = comedi_bytes_to_samples(s,
676 					      comedi_buf_read_n_available(s));
677 	if (nsamples > max_samples)
678 		nsamples = max_samples;
679 
680 	if (nsamples == 0)
681 		return 0;
682 
683 	nbytes = comedi_buf_read_alloc(s,
684 				       comedi_samples_to_bytes(s, nsamples));
685 	comedi_buf_memcpy_from(s, data, nbytes);
686 	comedi_buf_read_free(s, nbytes);
687 	comedi_inc_scan_progress(s, nbytes);
688 	s->async->events |= COMEDI_CB_BLOCK;
689 
690 	return nbytes;
691 }
692 EXPORT_SYMBOL_GPL(comedi_buf_read_samples);
693