sound/core/pcm_misc.c

   1 /*
   2  *  PCM Interface - misc routines
   3  *  Copyright (c) 1998 by Jaroslav Kysela <perex@perex.cz>
   4  *
   5  *
   6  *   This library is free software; you can redistribute it and/or modify
   7  *   it under the terms of the GNU Library General Public License as
   8  *   published by the Free Software Foundation; either version 2 of
   9  *   the License, or (at your option) any later version.
  10  *
  11  *   This program is distributed in the hope that it will be useful,
  12  *   but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  *   GNU Library General Public License for more details.
  15  *
  16  *   You should have received a copy of the GNU Library General Public
  17  *   License along with this library; if not, write to the Free Software
  18  *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
  19  *
  20  */
  21
  22 #include <linux/time.h>
  23 #include <linux/export.h>
  24 #include <sound/core.h>
  25 #include <sound/pcm.h>
  26 #define SND_PCM_FORMAT_UNKNOWN (-1)
  27
  28 /* NOTE: "signed" prefix must be given below since the default char is
  29  *       unsigned on some architectures!
  30  */
  31 struct pcm_format_data {
  32         unsigned char width;    /* bit width */
  33         unsigned char phys;     /* physical bit width */
  34         signed char le; /* 0 = big-endian, 1 = little-endian, -1 = others */
  35         signed char signd;      /* 0 = unsigned, 1 = signed, -1 = others */
  36         unsigned char silence[8];       /* silence data to fill */
  37 };
  38
  39 /* we do lots of calculations on snd_pcm_format_t; shut up sparse */
  40 #define INT     __force int
  41
  42 static struct pcm_format_data pcm_formats[(INT)SNDRV_PCM_FORMAT_LAST+1] = {
  43         [SNDRV_PCM_FORMAT_S8] = {
  44                 .width = 8, .phys = 8, .le = -1, .signd = 1,
  45                 .silence = {},
  46         },
  47         [SNDRV_PCM_FORMAT_U8] = {
  48                 .width = 8, .phys = 8, .le = -1, .signd = 0,
  49                 .silence = { 0x80 },
  50         },
  51         [SNDRV_PCM_FORMAT_S16_LE] = {
  52                 .width = 16, .phys = 16, .le = 1, .signd = 1,
  53                 .silence = {},
  54         },
  55         [SNDRV_PCM_FORMAT_S16_BE] = {
  56                 .width = 16, .phys = 16, .le = 0, .signd = 1,
  57                 .silence = {},
  58         },
  59         [SNDRV_PCM_FORMAT_U16_LE] = {
  60                 .width = 16, .phys = 16, .le = 1, .signd = 0,
  61                 .silence = { 0x00, 0x80 },
  62         },
  63         [SNDRV_PCM_FORMAT_U16_BE] = {
  64                 .width = 16, .phys = 16, .le = 0, .signd = 0,
  65                 .silence = { 0x80, 0x00 },
  66         },
  67         [SNDRV_PCM_FORMAT_S24_LE] = {
  68                 .width = 24, .phys = 32, .le = 1, .signd = 1,
  69                 .silence = {},
  70         },
  71         [SNDRV_PCM_FORMAT_S24_BE] = {
  72                 .width = 24, .phys = 32, .le = 0, .signd = 1,
  73                 .silence = {},
  74         },
  75         [SNDRV_PCM_FORMAT_U24_LE] = {
  76                 .width = 24, .phys = 32, .le = 1, .signd = 0,
  77                 .silence = { 0x00, 0x00, 0x80 },
  78         },
  79         [SNDRV_PCM_FORMAT_U24_BE] = {
  80                 .width = 24, .phys = 32, .le = 0, .signd = 0,
  81                 .silence = { 0x00, 0x80, 0x00, 0x00 },
  82         },
  83         [SNDRV_PCM_FORMAT_S32_LE] = {
  84                 .width = 32, .phys = 32, .le = 1, .signd = 1,
  85                 .silence = {},
  86         },
  87         [SNDRV_PCM_FORMAT_S32_BE] = {
  88                 .width = 32, .phys = 32, .le = 0, .signd = 1,
  89                 .silence = {},
  90         },
  91         [SNDRV_PCM_FORMAT_U32_LE] = {
  92                 .width = 32, .phys = 32, .le = 1, .signd = 0,
  93                 .silence = { 0x00, 0x00, 0x00, 0x80 },
  94         },
  95         [SNDRV_PCM_FORMAT_U32_BE] = {
  96                 .width = 32, .phys = 32, .le = 0, .signd = 0,
  97                 .silence = { 0x80, 0x00, 0x00, 0x00 },
  98         },
  99         [SNDRV_PCM_FORMAT_FLOAT_LE] = {
 100                 .width = 32, .phys = 32, .le = 1, .signd = -1,
 101                 .silence = {},
 102         },
 103         [SNDRV_PCM_FORMAT_FLOAT_BE] = {
 104                 .width = 32, .phys = 32, .le = 0, .signd = -1,
 105                 .silence = {},
 106         },
 107         [SNDRV_PCM_FORMAT_FLOAT64_LE] = {
 108                 .width = 64, .phys = 64, .le = 1, .signd = -1,
 109                 .silence = {},
 110         },
 111         [SNDRV_PCM_FORMAT_FLOAT64_BE] = {
 112                 .width = 64, .phys = 64, .le = 0, .signd = -1,
 113                 .silence = {},
 114         },
 115         [SNDRV_PCM_FORMAT_IEC958_SUBFRAME_LE] = {
 116                 .width = 32, .phys = 32, .le = 1, .signd = -1,
 117                 .silence = {},
 118         },
 119         [SNDRV_PCM_FORMAT_IEC958_SUBFRAME_BE] = {
 120                 .width = 32, .phys = 32, .le = 0, .signd = -1,
 121                 .silence = {},
 122         },
 123         [SNDRV_PCM_FORMAT_MU_LAW] = {
 124                 .width = 8, .phys = 8, .le = -1, .signd = -1,
 125                 .silence = { 0x7f },
 126         },
 127         [SNDRV_PCM_FORMAT_A_LAW] = {
 128                 .width = 8, .phys = 8, .le = -1, .signd = -1,
 129                 .silence = { 0x55 },
 130         },
 131         [SNDRV_PCM_FORMAT_IMA_ADPCM] = {
 132                 .width = 4, .phys = 4, .le = -1, .signd = -1,
 133                 .silence = {},
 134         },
 135         [SNDRV_PCM_FORMAT_G723_24] = {
 136                 .width = 3, .phys = 3, .le = -1, .signd = -1,
 137                 .silence = {},
 138         },
 139         [SNDRV_PCM_FORMAT_G723_40] = {
 140                 .width = 5, .phys = 5, .le = -1, .signd = -1,
 141                 .silence = {},
 142         },
 143         [SNDRV_PCM_FORMAT_DSD_U8] = {
 144                 .width = 8, .phys = 8, .le = 1, .signd = 0,
 145                 .silence = { 0x69 },
 146         },
 147         [SNDRV_PCM_FORMAT_DSD_U16_LE] = {
 148                 .width = 16, .phys = 16, .le = 1, .signd = 0,
 149                 .silence = { 0x69, 0x69 },
 150         },
 151         [SNDRV_PCM_FORMAT_DSD_U32_LE] = {
 152                 .width = 32, .phys = 32, .le = 1, .signd = 0,
 153                 .silence = { 0x69, 0x69, 0x69, 0x69 },
 154         },
 155         [SNDRV_PCM_FORMAT_DSD_U16_BE] = {
 156                 .width = 16, .phys = 16, .le = 0, .signd = 0,
 157                 .silence = { 0x69, 0x69 },
 158         },
 159         [SNDRV_PCM_FORMAT_DSD_U32_BE] = {
 160                 .width = 32, .phys = 32, .le = 0, .signd = 0,
 161                 .silence = { 0x69, 0x69, 0x69, 0x69 },
 162         },
 163         /* FIXME: the following three formats are not defined properly yet */
 164         [SNDRV_PCM_FORMAT_MPEG] = {
 165                 .le = -1, .signd = -1,
 166         },
 167         [SNDRV_PCM_FORMAT_GSM] = {
 168                 .le = -1, .signd = -1,
 169         },
 170         [SNDRV_PCM_FORMAT_SPECIAL] = {
 171                 .le = -1, .signd = -1,
 172         },
 173         [SNDRV_PCM_FORMAT_S24_3LE] = {
 174                 .width = 24, .phys = 24, .le = 1, .signd = 1,
 175                 .silence = {},
 176         },
 177         [SNDRV_PCM_FORMAT_S24_3BE] = {
 178                 .width = 24, .phys = 24, .le = 0, .signd = 1,
 179                 .silence = {},
 180         },
 181         [SNDRV_PCM_FORMAT_U24_3LE] = {
 182                 .width = 24, .phys = 24, .le = 1, .signd = 0,
 183                 .silence = { 0x00, 0x00, 0x80 },
 184         },
 185         [SNDRV_PCM_FORMAT_U24_3BE] = {
 186                 .width = 24, .phys = 24, .le = 0, .signd = 0,
 187                 .silence = { 0x80, 0x00, 0x00 },
 188         },
 189         [SNDRV_PCM_FORMAT_S20_3LE] = {
 190                 .width = 20, .phys = 24, .le = 1, .signd = 1,
 191                 .silence = {},
 192         },
 193         [SNDRV_PCM_FORMAT_S20_3BE] = {
 194                 .width = 20, .phys = 24, .le = 0, .signd = 1,
 195                 .silence = {},
 196         },
 197         [SNDRV_PCM_FORMAT_U20_3LE] = {
 198                 .width = 20, .phys = 24, .le = 1, .signd = 0,
 199                 .silence = { 0x00, 0x00, 0x08 },
 200         },
 201         [SNDRV_PCM_FORMAT_U20_3BE] = {
 202                 .width = 20, .phys = 24, .le = 0, .signd = 0,
 203                 .silence = { 0x08, 0x00, 0x00 },
 204         },
 205         [SNDRV_PCM_FORMAT_S18_3LE] = {
 206                 .width = 18, .phys = 24, .le = 1, .signd = 1,
 207                 .silence = {},
 208         },
 209         [SNDRV_PCM_FORMAT_S18_3BE] = {
 210                 .width = 18, .phys = 24, .le = 0, .signd = 1,
 211                 .silence = {},
 212         },
 213         [SNDRV_PCM_FORMAT_U18_3LE] = {
 214                 .width = 18, .phys = 24, .le = 1, .signd = 0,
 215                 .silence = { 0x00, 0x00, 0x02 },
 216         },
 217         [SNDRV_PCM_FORMAT_U18_3BE] = {
 218                 .width = 18, .phys = 24, .le = 0, .signd = 0,
 219                 .silence = { 0x02, 0x00, 0x00 },
 220         },
 221         [SNDRV_PCM_FORMAT_G723_24_1B] = {
 222                 .width = 3, .phys = 8, .le = -1, .signd = -1,
 223                 .silence = {},
 224         },
 225         [SNDRV_PCM_FORMAT_G723_40_1B] = {
 226                 .width = 5, .phys = 8, .le = -1, .signd = -1,
 227                 .silence = {},
 228         },
 229 };
 230
 231
 232 /**
 233  * snd_pcm_format_signed - Check the PCM format is signed linear
 234  * @format: the format to check
 235  *
 236  * Return: 1 if the given PCM format is signed linear, 0 if unsigned
 237  * linear, and a negative error code for non-linear formats.
 238  */
 239 int snd_pcm_format_signed(snd_pcm_format_t format)
 240 {
 241         int val;
 242         if ((INT)format < 0 || (INT)format > (INT)SNDRV_PCM_FORMAT_LAST)
 243                 return -EINVAL;
 244         if ((val = pcm_formats[(INT)format].signd) < 0)
 245                 return -EINVAL;
 246         return val;
 247 }
 248
 249 EXPORT_SYMBOL(snd_pcm_format_signed);
 250
 251 /**
 252  * snd_pcm_format_unsigned - Check the PCM format is unsigned linear
 253  * @format: the format to check
 254  *
 255  * Return: 1 if the given PCM format is unsigned linear, 0 if signed
 256  * linear, and a negative error code for non-linear formats.
 257  */
 258 int snd_pcm_format_unsigned(snd_pcm_format_t format)
 259 {
 260         int val;
 261
 262         val = snd_pcm_format_signed(format);
 263         if (val < 0)
 264                 return val;
 265         return !val;
 266 }
 267
 268 EXPORT_SYMBOL(snd_pcm_format_unsigned);
 269
 270 /**
 271  * snd_pcm_format_linear - Check the PCM format is linear
 272  * @format: the format to check
 273  *
 274  * Return: 1 if the given PCM format is linear, 0 if not.
 275  */
 276 int snd_pcm_format_linear(snd_pcm_format_t format)
 277 {
 278         return snd_pcm_format_signed(format) >= 0;
 279 }
 280
 281 EXPORT_SYMBOL(snd_pcm_format_linear);
 282
 283 /**
 284  * snd_pcm_format_little_endian - Check the PCM format is little-endian
 285  * @format: the format to check
 286  *
 287  * Return: 1 if the given PCM format is little-endian, 0 if
 288  * big-endian, or a negative error code if endian not specified.
 289  */
 290 int snd_pcm_format_little_endian(snd_pcm_format_t format)
 291 {
 292         int val;
 293         if ((INT)format < 0 || (INT)format > (INT)SNDRV_PCM_FORMAT_LAST)
 294                 return -EINVAL;
 295         if ((val = pcm_formats[(INT)format].le) < 0)
 296                 return -EINVAL;
 297         return val;
 298 }
 299
 300 EXPORT_SYMBOL(snd_pcm_format_little_endian);
 301
 302 /**
 303  * snd_pcm_format_big_endian - Check the PCM format is big-endian
 304  * @format: the format to check
 305  *
 306  * Return: 1 if the given PCM format is big-endian, 0 if
 307  * little-endian, or a negative error code if endian not specified.
 308  */
 309 int snd_pcm_format_big_endian(snd_pcm_format_t format)
 310 {
 311         int val;
 312
 313         val = snd_pcm_format_little_endian(format);
 314         if (val < 0)
 315                 return val;
 316         return !val;
 317 }
 318
 319 EXPORT_SYMBOL(snd_pcm_format_big_endian);
 320
 321 /**
 322  * snd_pcm_format_width - return the bit-width of the format
 323  * @format: the format to check
 324  *
 325  * Return: The bit-width of the format, or a negative error code
 326  * if unknown format.
 327  */
 328 int snd_pcm_format_width(snd_pcm_format_t format)
 329 {
 330         int val;
 331         if ((INT)format < 0 || (INT)format > (INT)SNDRV_PCM_FORMAT_LAST)
 332                 return -EINVAL;
 333         if ((val = pcm_formats[(INT)format].width) == 0)
 334                 return -EINVAL;
 335         return val;
 336 }
 337
 338 EXPORT_SYMBOL(snd_pcm_format_width);
 339
 340 /**
 341  * snd_pcm_format_physical_width - return the physical bit-width of the format
 342  * @format: the format to check
 343  *
 344  * Return: The physical bit-width of the format, or a negative error code
 345  * if unknown format.
 346  */
 347 int snd_pcm_format_physical_width(snd_pcm_format_t format)
 348 {
 349         int val;
 350         if ((INT)format < 0 || (INT)format > (INT)SNDRV_PCM_FORMAT_LAST)
 351                 return -EINVAL;
 352         if ((val = pcm_formats[(INT)format].phys) == 0)
 353                 return -EINVAL;
 354         return val;
 355 }
 356
 357 EXPORT_SYMBOL(snd_pcm_format_physical_width);
 358
 359 /**
 360  * snd_pcm_format_size - return the byte size of samples on the given format
 361  * @format: the format to check
 362  * @samples: sampling rate
 363  *
 364  * Return: The byte size of the given samples for the format, or a
 365  * negative error code if unknown format.
 366  */
 367 ssize_t snd_pcm_format_size(snd_pcm_format_t format, size_t samples)
 368 {
 369         int phys_width = snd_pcm_format_physical_width(format);
 370         if (phys_width < 0)
 371                 return -EINVAL;
 372         return samples * phys_width / 8;
 373 }
 374
 375 EXPORT_SYMBOL(snd_pcm_format_size);
 376
 377 /**
 378  * snd_pcm_format_silence_64 - return the silent data in 8 bytes array
 379  * @format: the format to check
 380  *
 381  * Return: The format pattern to fill or %NULL if error.
 382  */
 383 const unsigned char *snd_pcm_format_silence_64(snd_pcm_format_t format)
 384 {
 385         if ((INT)format < 0 || (INT)format > (INT)SNDRV_PCM_FORMAT_LAST)
 386                 return NULL;
 387         if (! pcm_formats[(INT)format].phys)
 388                 return NULL;
 389         return pcm_formats[(INT)format].silence;
 390 }
 391
 392 EXPORT_SYMBOL(snd_pcm_format_silence_64);
 393
 394 /**
 395  * snd_pcm_format_set_silence - set the silence data on the buffer
 396  * @format: the PCM format
 397  * @data: the buffer pointer
 398  * @samples: the number of samples to set silence
 399  *
 400  * Sets the silence data on the buffer for the given samples.
 401  *
 402  * Return: Zero if successful, or a negative error code on failure.
 403  */
 404 int snd_pcm_format_set_silence(snd_pcm_format_t format, void *data, unsigned int samples)
 405 {
 406         int width;
 407         unsigned char *dst, *pat;
 408
 409         if ((INT)format < 0 || (INT)format > (INT)SNDRV_PCM_FORMAT_LAST)
 410                 return -EINVAL;
 411         if (samples == 0)
 412                 return 0;
 413         width = pcm_formats[(INT)format].phys; /* physical width */
 414         pat = pcm_formats[(INT)format].silence;
 415         if (! width)
 416                 return -EINVAL;
 417         /* signed or 1 byte data */
 418         if (pcm_formats[(INT)format].signd == 1 || width <= 8) {
 419                 unsigned int bytes = samples * width / 8;
 420                 memset(data, *pat, bytes);
 421                 return 0;
 422         }
 423         /* non-zero samples, fill using a loop */
 424         width /= 8;
 425         dst = data;
 426 #if 0
 427         while (samples--) {
 428                 memcpy(dst, pat, width);
 429                 dst += width;
 430         }
 431 #else
 432         /* a bit optimization for constant width */
 433         switch (width) {
 434         case 2:
 435                 while (samples--) {
 436                         memcpy(dst, pat, 2);
 437                         dst += 2;
 438                 }
 439                 break;
 440         case 3:
 441                 while (samples--) {
 442                         memcpy(dst, pat, 3);
 443                         dst += 3;
 444                 }
 445                 break;
 446         case 4:
 447                 while (samples--) {
 448                         memcpy(dst, pat, 4);
 449                         dst += 4;
 450                 }
 451                 break;
 452         case 8:
 453                 while (samples--) {
 454                         memcpy(dst, pat, 8);
 455                         dst += 8;
 456                 }
 457                 break;
 458         }
 459 #endif
 460         return 0;
 461 }
 462
 463 EXPORT_SYMBOL(snd_pcm_format_set_silence);
 464
 465 /**
 466  * snd_pcm_limit_hw_rates - determine rate_min/rate_max fields
 467  * @runtime: the runtime instance
 468  *
 469  * Determines the rate_min and rate_max fields from the rates bits of
 470  * the given runtime->hw.
 471  *
 472  * Return: Zero if successful.
 473  */
 474 int snd_pcm_limit_hw_rates(struct snd_pcm_runtime *runtime)
 475 {
 476         int i;
 477         for (i = 0; i < (int)snd_pcm_known_rates.count; i++) {
 478                 if (runtime->hw.rates & (1 << i)) {
 479                         runtime->hw.rate_min = snd_pcm_known_rates.list[i];
 480                         break;
 481                 }
 482         }
 483         for (i = (int)snd_pcm_known_rates.count - 1; i >= 0; i--) {
 484                 if (runtime->hw.rates & (1 << i)) {
 485                         runtime->hw.rate_max = snd_pcm_known_rates.list[i];
 486                         break;
 487                 }
 488         }
 489         return 0;
 490 }
 491
 492 EXPORT_SYMBOL(snd_pcm_limit_hw_rates);
 493
 494 /**
 495  * snd_pcm_rate_to_rate_bit - converts sample rate to SNDRV_PCM_RATE_xxx bit
 496  * @rate: the sample rate to convert
 497  *
 498  * Return: The SNDRV_PCM_RATE_xxx flag that corresponds to the given rate, or
 499  * SNDRV_PCM_RATE_KNOT for an unknown rate.
 500  */
 501 unsigned int snd_pcm_rate_to_rate_bit(unsigned int rate)
 502 {
 503         unsigned int i;
 504
 505         for (i = 0; i < snd_pcm_known_rates.count; i++)
 506                 if (snd_pcm_known_rates.list[i] == rate)
 507                         return 1u << i;
 508         return SNDRV_PCM_RATE_KNOT;
 509 }
 510 EXPORT_SYMBOL(snd_pcm_rate_to_rate_bit);
 511
 512 /**
 513  * snd_pcm_rate_bit_to_rate - converts SNDRV_PCM_RATE_xxx bit to sample rate
 514  * @rate_bit: the rate bit to convert
 515  *
 516  * Return: The sample rate that corresponds to the given SNDRV_PCM_RATE_xxx flag
 517  * or 0 for an unknown rate bit.
 518  */
 519 unsigned int snd_pcm_rate_bit_to_rate(unsigned int rate_bit)
 520 {
 521         unsigned int i;
 522
 523         for (i = 0; i < snd_pcm_known_rates.count; i++)
 524                 if ((1u << i) == rate_bit)
 525                         return snd_pcm_known_rates.list[i];
 526         return 0;
 527 }
 528 EXPORT_SYMBOL(snd_pcm_rate_bit_to_rate);
 529
 530 static unsigned int snd_pcm_rate_mask_sanitize(unsigned int rates)
 531 {
 532         if (rates & SNDRV_PCM_RATE_CONTINUOUS)
 533                 return SNDRV_PCM_RATE_CONTINUOUS;
 534         else if (rates & SNDRV_PCM_RATE_KNOT)
 535                 return SNDRV_PCM_RATE_KNOT;
 536         return rates;
 537 }
 538
 539 /**
 540  * snd_pcm_rate_mask_intersect - computes the intersection between two rate masks
 541  * @rates_a: The first rate mask
 542  * @rates_b: The second rate mask
 543  *
 544  * This function computes the rates that are supported by both rate masks passed
 545  * to the function. It will take care of the special handling of
 546  * SNDRV_PCM_RATE_CONTINUOUS and SNDRV_PCM_RATE_KNOT.
 547  *
 548  * Return: A rate mask containing the rates that are supported by both rates_a
 549  * and rates_b.
 550  */
 551 unsigned int snd_pcm_rate_mask_intersect(unsigned int rates_a,
 552         unsigned int rates_b)
 553 {
 554         rates_a = snd_pcm_rate_mask_sanitize(rates_a);
 555         rates_b = snd_pcm_rate_mask_sanitize(rates_b);
 556
 557         if (rates_a & SNDRV_PCM_RATE_CONTINUOUS)
 558                 return rates_b;
 559         else if (rates_b & SNDRV_PCM_RATE_CONTINUOUS)
 560                 return rates_a;
 561         else if (rates_a & SNDRV_PCM_RATE_KNOT)
 562                 return rates_b;
 563         else if (rates_b & SNDRV_PCM_RATE_KNOT)
 564                 return rates_a;
 565         return rates_a & rates_b;
 566 }
 567 EXPORT_SYMBOL_GPL(snd_pcm_rate_mask_intersect);
 568
 569 /**
 570  * snd_pcm_rate_range_to_bits - converts rate range to SNDRV_PCM_RATE_xxx bit
 571  * @rate_min: the minimum sample rate
 572  * @rate_max: the maximum sample rate
 573  *
 574  * This function has an implicit assumption: the rates in the given range have
 575  * only the pre-defined rates like 44100 or 16000.
 576  *
 577  * Return: The SNDRV_PCM_RATE_xxx flag that corresponds to the given rate range,
 578  * or SNDRV_PCM_RATE_KNOT for an unknown range.
 579  */
 580 unsigned int snd_pcm_rate_range_to_bits(unsigned int rate_min,
 581         unsigned int rate_max)
 582 {
 583         unsigned int rates = 0;
 584         int i;
 585
 586         for (i = 0; i < snd_pcm_known_rates.count; i++) {
 587                 if (snd_pcm_known_rates.list[i] >= rate_min
 588                         && snd_pcm_known_rates.list[i] <= rate_max)
 589                         rates |= 1 << i;
 590         }
 591
 592         if (!rates)
 593                 rates = SNDRV_PCM_RATE_KNOT;
 594
 595         return rates;
 596 }
 597 EXPORT_SYMBOL_GPL(snd_pcm_rate_range_to_bits);