root/drivers/staging/comedi/comedi_buf.c

DEFINITIONS

1. comedi_buf_map_kref_release
2. __comedi_buf_free
3. comedi_buf_map_alloc
4. __comedi_buf_alloc
5. comedi_buf_map_get
6. comedi_buf_map_put
7. comedi_buf_map_access
8. comedi_buf_map_from_subdev_get
9. comedi_buf_is_mmapped
10. comedi_buf_alloc
11. comedi_buf_reset
12. comedi_buf_write_n_unalloc
13. comedi_buf_write_n_available
14. comedi_buf_write_alloc
15. comedi_buf_munge
16. comedi_buf_write_n_allocated
17. comedi_buf_write_free
18. comedi_buf_read_n_available
19. comedi_buf_read_alloc
20. comedi_buf_read_n_allocated
21. comedi_buf_read_free
22. comedi_buf_memcpy_to
23. comedi_buf_memcpy_from
24. comedi_buf_write_samples
25. comedi_buf_read_samples

   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 
  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 
  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 *
  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 
 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 
 190 void comedi_buf_map_get(struct comedi_buf_map *bm)
 191 {
 192         if (bm)
 193                 kref_get(&bm->refcount);
 194 }
 195 
 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 */
 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 *
 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 
 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 
 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 
 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 
 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 
 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  */
 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  */
 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                 count = num_bytes;
 375         } else {
 376                 /* don't munge partial samples */
 377                 num_bytes -= num_bytes % num_sample_bytes;
 378                 while (count < num_bytes) {
 379                         int block_size = num_bytes - count;
 380                         unsigned int buf_end;
 381 
 382                         buf_end = async->prealloc_bufsz - async->munge_ptr;
 383                         if (block_size > buf_end)
 384                                 block_size = buf_end;
 385 
 386                         s->munge(s->device, s,
 387                                  async->prealloc_buf + async->munge_ptr,
 388                                  block_size, async->munge_chan);
 389 
 390                         /*
 391                          * ensure data is munged in buffer before the
 392                          * async buffer munge_count is incremented
 393                          */
 394                         smp_wmb();
 395 
 396                         async->munge_chan += block_size / num_sample_bytes;
 397                         async->munge_chan %= async->cmd.chanlist_len;
 398                         async->munge_count += block_size;
 399                         async->munge_ptr += block_size;
 400                         async->munge_ptr %= async->prealloc_bufsz;
 401                         count += block_size;
 402                 }
 403         }
 404 
 405         return count;
 406 }
 407 
 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  */
 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  */
 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  */
 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 
 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  */
 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 
 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 
 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  */
 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  */
 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);