drivers/usb/gadget/function/u_audio.c

   1 // SPDX-License-Identifier: GPL-2.0+
   2 /*
   3  * u_audio.c -- interface to USB gadget "ALSA sound card" utilities
   4  *
   5  * Copyright (C) 2016
   6  * Author: Ruslan Bilovol <ruslan.bilovol@gmail.com>
   7  *
   8  * Sound card implementation was cut-and-pasted with changes
   9  * from f_uac2.c and has:
  10  *    Copyright (C) 2011
  11  *    Yadwinder Singh (yadi.brar01@gmail.com)
  12  *    Jaswinder Singh (jaswinder.singh@linaro.org)
  13  */
  14
  15 #include <linux/module.h>
  16 #include <sound/core.h>
  17 #include <sound/pcm.h>
  18 #include <sound/pcm_params.h>
  19
  20 #include "u_audio.h"
  21
  22 #define BUFF_SIZE_MAX   (PAGE_SIZE * 16)
  23 #define PRD_SIZE_MAX    PAGE_SIZE
  24 #define MIN_PERIODS     4
  25
  26 struct uac_req {
  27         struct uac_rtd_params *pp; /* parent param */
  28         struct usb_request *req;
  29 };
  30
  31 /* Runtime data params for one stream */
  32 struct uac_rtd_params {
  33         struct snd_uac_chip *uac; /* parent chip */
  34         bool ep_enabled; /* if the ep is enabled */
  35         /* Size of the ring buffer */
  36         size_t dma_bytes;
  37         unsigned char *dma_area;
  38
  39         struct snd_pcm_substream *ss;
  40
  41         /* Ring buffer */
  42         ssize_t hw_ptr;
  43
  44         void *rbuf;
  45
  46         size_t period_size;
  47
  48         unsigned max_psize;     /* MaxPacketSize of endpoint */
  49         struct uac_req *ureq;
  50
  51         spinlock_t lock;
  52 };
  53
  54 struct snd_uac_chip {
  55         struct g_audio *audio_dev;
  56
  57         struct uac_rtd_params p_prm;
  58         struct uac_rtd_params c_prm;
  59
  60         struct snd_card *card;
  61         struct snd_pcm *pcm;
  62
  63         /* timekeeping for the playback endpoint */
  64         unsigned int p_interval;
  65         unsigned int p_residue;
  66
  67         /* pre-calculated values for playback iso completion */
  68         unsigned int p_pktsize;
  69         unsigned int p_pktsize_residue;
  70         unsigned int p_framesize;
  71 };
  72
  73 static const struct snd_pcm_hardware uac_pcm_hardware = {
  74         .info = SNDRV_PCM_INFO_INTERLEAVED | SNDRV_PCM_INFO_BLOCK_TRANSFER
  75                  | SNDRV_PCM_INFO_MMAP | SNDRV_PCM_INFO_MMAP_VALID
  76                  | SNDRV_PCM_INFO_PAUSE | SNDRV_PCM_INFO_RESUME,
  77         .rates = SNDRV_PCM_RATE_CONTINUOUS,
  78         .periods_max = BUFF_SIZE_MAX / PRD_SIZE_MAX,
  79         .buffer_bytes_max = BUFF_SIZE_MAX,
  80         .period_bytes_max = PRD_SIZE_MAX,
  81         .periods_min = MIN_PERIODS,
  82 };
  83
  84 static void u_audio_iso_complete(struct usb_ep *ep, struct usb_request *req)
  85 {
  86         unsigned pending;
  87         unsigned long flags;
  88         unsigned int hw_ptr;
  89         bool update_alsa = false;
  90         int status = req->status;
  91         struct uac_req *ur = req->context;
  92         struct snd_pcm_substream *substream;
  93         struct uac_rtd_params *prm = ur->pp;
  94         struct snd_uac_chip *uac = prm->uac;
  95
  96         /* i/f shutting down */
  97         if (!prm->ep_enabled || req->status == -ESHUTDOWN)
  98                 return;
  99
 100         /*
 101          * We can't really do much about bad xfers.
 102          * Afterall, the ISOCH xfers could fail legitimately.
 103          */
 104         if (status)
 105                 pr_debug("%s: iso_complete status(%d) %d/%d\n",
 106                         __func__, status, req->actual, req->length);
 107
 108         substream = prm->ss;
 109
 110         /* Do nothing if ALSA isn't active */
 111         if (!substream)
 112                 goto exit;
 113
 114         spin_lock_irqsave(&prm->lock, flags);
 115
 116         if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) {
 117                 /*
 118                  * For each IN packet, take the quotient of the current data
 119                  * rate and the endpoint's interval as the base packet size.
 120                  * If there is a residue from this division, add it to the
 121                  * residue accumulator.
 122                  */
 123                 req->length = uac->p_pktsize;
 124                 uac->p_residue += uac->p_pktsize_residue;
 125
 126                 /*
 127                  * Whenever there are more bytes in the accumulator than we
 128                  * need to add one more sample frame, increase this packet's
 129                  * size and decrease the accumulator.
 130                  */
 131                 if (uac->p_residue / uac->p_interval >= uac->p_framesize) {
 132                         req->length += uac->p_framesize;
 133                         uac->p_residue -= uac->p_framesize *
 134                                            uac->p_interval;
 135                 }
 136
 137                 req->actual = req->length;
 138         }
 139
 140         pending = prm->hw_ptr % prm->period_size;
 141         pending += req->actual;
 142         if (pending >= prm->period_size)
 143                 update_alsa = true;
 144
 145         hw_ptr = prm->hw_ptr;
 146         prm->hw_ptr = (prm->hw_ptr + req->actual) % prm->dma_bytes;
 147
 148         spin_unlock_irqrestore(&prm->lock, flags);
 149
 150         /* Pack USB load in ALSA ring buffer */
 151         pending = prm->dma_bytes - hw_ptr;
 152
 153         if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) {
 154                 if (unlikely(pending < req->actual)) {
 155                         memcpy(req->buf, prm->dma_area + hw_ptr, pending);
 156                         memcpy(req->buf + pending, prm->dma_area,
 157                                req->actual - pending);
 158                 } else {
 159                         memcpy(req->buf, prm->dma_area + hw_ptr, req->actual);
 160                 }
 161         } else {
 162                 if (unlikely(pending < req->actual)) {
 163                         memcpy(prm->dma_area + hw_ptr, req->buf, pending);
 164                         memcpy(prm->dma_area, req->buf + pending,
 165                                req->actual - pending);
 166                 } else {
 167                         memcpy(prm->dma_area + hw_ptr, req->buf, req->actual);
 168                 }
 169         }
 170
 171 exit:
 172         if (usb_ep_queue(ep, req, GFP_ATOMIC))
 173                 dev_err(uac->card->dev, "%d Error!\n", __LINE__);
 174
 175         if (update_alsa)
 176                 snd_pcm_period_elapsed(substream);
 177 }
 178
 179 static int uac_pcm_trigger(struct snd_pcm_substream *substream, int cmd)
 180 {
 181         struct snd_uac_chip *uac = snd_pcm_substream_chip(substream);
 182         struct uac_rtd_params *prm;
 183         struct g_audio *audio_dev;
 184         struct uac_params *params;
 185         unsigned long flags;
 186         int err = 0;
 187
 188         audio_dev = uac->audio_dev;
 189         params = &audio_dev->params;
 190
 191         if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
 192                 prm = &uac->p_prm;
 193         else
 194                 prm = &uac->c_prm;
 195
 196         spin_lock_irqsave(&prm->lock, flags);
 197
 198         /* Reset */
 199         prm->hw_ptr = 0;
 200
 201         switch (cmd) {
 202         case SNDRV_PCM_TRIGGER_START:
 203         case SNDRV_PCM_TRIGGER_RESUME:
 204                 prm->ss = substream;
 205                 break;
 206         case SNDRV_PCM_TRIGGER_STOP:
 207         case SNDRV_PCM_TRIGGER_SUSPEND:
 208                 prm->ss = NULL;
 209                 break;
 210         default:
 211                 err = -EINVAL;
 212         }
 213
 214         spin_unlock_irqrestore(&prm->lock, flags);
 215
 216         /* Clear buffer after Play stops */
 217         if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK && !prm->ss)
 218                 memset(prm->rbuf, 0, prm->max_psize * params->req_number);
 219
 220         return err;
 221 }
 222
 223 static snd_pcm_uframes_t uac_pcm_pointer(struct snd_pcm_substream *substream)
 224 {
 225         struct snd_uac_chip *uac = snd_pcm_substream_chip(substream);
 226         struct uac_rtd_params *prm;
 227
 228         if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
 229                 prm = &uac->p_prm;
 230         else
 231                 prm = &uac->c_prm;
 232
 233         return bytes_to_frames(substream->runtime, prm->hw_ptr);
 234 }
 235
 236 static int uac_pcm_hw_params(struct snd_pcm_substream *substream,
 237                                struct snd_pcm_hw_params *hw_params)
 238 {
 239         struct snd_uac_chip *uac = snd_pcm_substream_chip(substream);
 240         struct uac_rtd_params *prm;
 241         int err;
 242
 243         if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
 244                 prm = &uac->p_prm;
 245         else
 246                 prm = &uac->c_prm;
 247
 248         err = snd_pcm_lib_malloc_pages(substream,
 249                                         params_buffer_bytes(hw_params));
 250         if (err >= 0) {
 251                 prm->dma_bytes = substream->runtime->dma_bytes;
 252                 prm->dma_area = substream->runtime->dma_area;
 253                 prm->period_size = params_period_bytes(hw_params);
 254         }
 255
 256         return err;
 257 }
 258
 259 static int uac_pcm_hw_free(struct snd_pcm_substream *substream)
 260 {
 261         struct snd_uac_chip *uac = snd_pcm_substream_chip(substream);
 262         struct uac_rtd_params *prm;
 263
 264         if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
 265                 prm = &uac->p_prm;
 266         else
 267                 prm = &uac->c_prm;
 268
 269         prm->dma_area = NULL;
 270         prm->dma_bytes = 0;
 271         prm->period_size = 0;
 272
 273         return snd_pcm_lib_free_pages(substream);
 274 }
 275
 276 static int uac_pcm_open(struct snd_pcm_substream *substream)
 277 {
 278         struct snd_uac_chip *uac = snd_pcm_substream_chip(substream);
 279         struct snd_pcm_runtime *runtime = substream->runtime;
 280         struct g_audio *audio_dev;
 281         struct uac_params *params;
 282         int p_ssize, c_ssize;
 283         int p_srate, c_srate;
 284         int p_chmask, c_chmask;
 285
 286         audio_dev = uac->audio_dev;
 287         params = &audio_dev->params;
 288         p_ssize = params->p_ssize;
 289         c_ssize = params->c_ssize;
 290         p_srate = params->p_srate;
 291         c_srate = params->c_srate;
 292         p_chmask = params->p_chmask;
 293         c_chmask = params->c_chmask;
 294         uac->p_residue = 0;
 295
 296         runtime->hw = uac_pcm_hardware;
 297
 298         if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) {
 299                 spin_lock_init(&uac->p_prm.lock);
 300                 runtime->hw.rate_min = p_srate;
 301                 switch (p_ssize) {
 302                 case 3:
 303                         runtime->hw.formats = SNDRV_PCM_FMTBIT_S24_3LE;
 304                         break;
 305                 case 4:
 306                         runtime->hw.formats = SNDRV_PCM_FMTBIT_S32_LE;
 307                         break;
 308                 default:
 309                         runtime->hw.formats = SNDRV_PCM_FMTBIT_S16_LE;
 310                         break;
 311                 }
 312                 runtime->hw.channels_min = num_channels(p_chmask);
 313                 runtime->hw.period_bytes_min = 2 * uac->p_prm.max_psize
 314                                                 / runtime->hw.periods_min;
 315         } else {
 316                 spin_lock_init(&uac->c_prm.lock);
 317                 runtime->hw.rate_min = c_srate;
 318                 switch (c_ssize) {
 319                 case 3:
 320                         runtime->hw.formats = SNDRV_PCM_FMTBIT_S24_3LE;
 321                         break;
 322                 case 4:
 323                         runtime->hw.formats = SNDRV_PCM_FMTBIT_S32_LE;
 324                         break;
 325                 default:
 326                         runtime->hw.formats = SNDRV_PCM_FMTBIT_S16_LE;
 327                         break;
 328                 }
 329                 runtime->hw.channels_min = num_channels(c_chmask);
 330                 runtime->hw.period_bytes_min = 2 * uac->c_prm.max_psize
 331                                                 / runtime->hw.periods_min;
 332         }
 333
 334         runtime->hw.rate_max = runtime->hw.rate_min;
 335         runtime->hw.channels_max = runtime->hw.channels_min;
 336
 337         snd_pcm_hw_constraint_integer(runtime, SNDRV_PCM_HW_PARAM_PERIODS);
 338
 339         return 0;
 340 }
 341
 342 /* ALSA cries without these function pointers */
 343 static int uac_pcm_null(struct snd_pcm_substream *substream)
 344 {
 345         return 0;
 346 }
 347
 348 static const struct snd_pcm_ops uac_pcm_ops = {
 349         .open = uac_pcm_open,
 350         .close = uac_pcm_null,
 351         .ioctl = snd_pcm_lib_ioctl,
 352         .hw_params = uac_pcm_hw_params,
 353         .hw_free = uac_pcm_hw_free,
 354         .trigger = uac_pcm_trigger,
 355         .pointer = uac_pcm_pointer,
 356         .prepare = uac_pcm_null,
 357 };
 358
 359 static inline void free_ep(struct uac_rtd_params *prm, struct usb_ep *ep)
 360 {
 361         struct snd_uac_chip *uac = prm->uac;
 362         struct g_audio *audio_dev;
 363         struct uac_params *params;
 364         int i;
 365
 366         if (!prm->ep_enabled)
 367                 return;
 368
 369         prm->ep_enabled = false;
 370
 371         audio_dev = uac->audio_dev;
 372         params = &audio_dev->params;
 373
 374         for (i = 0; i < params->req_number; i++) {
 375                 if (prm->ureq[i].req) {
 376                         usb_ep_dequeue(ep, prm->ureq[i].req);
 377                         usb_ep_free_request(ep, prm->ureq[i].req);
 378                         prm->ureq[i].req = NULL;
 379                 }
 380         }
 381
 382         if (usb_ep_disable(ep))
 383                 dev_err(uac->card->dev, "%s:%d Error!\n", __func__, __LINE__);
 384 }
 385
 386
 387 int u_audio_start_capture(struct g_audio *audio_dev)
 388 {
 389         struct snd_uac_chip *uac = audio_dev->uac;
 390         struct usb_gadget *gadget = audio_dev->gadget;
 391         struct device *dev = &gadget->dev;
 392         struct usb_request *req;
 393         struct usb_ep *ep;
 394         struct uac_rtd_params *prm;
 395         struct uac_params *params = &audio_dev->params;
 396         int req_len, i;
 397
 398         ep = audio_dev->out_ep;
 399         prm = &uac->c_prm;
 400         config_ep_by_speed(gadget, &audio_dev->func, ep);
 401         req_len = prm->max_psize;
 402
 403         prm->ep_enabled = true;
 404         usb_ep_enable(ep);
 405
 406         for (i = 0; i < params->req_number; i++) {
 407                 if (!prm->ureq[i].req) {
 408                         req = usb_ep_alloc_request(ep, GFP_ATOMIC);
 409                         if (req == NULL)
 410                                 return -ENOMEM;
 411
 412                         prm->ureq[i].req = req;
 413                         prm->ureq[i].pp = prm;
 414
 415                         req->zero = 0;
 416                         req->context = &prm->ureq[i];
 417                         req->length = req_len;
 418                         req->complete = u_audio_iso_complete;
 419                         req->buf = prm->rbuf + i * prm->max_psize;
 420                 }
 421
 422                 if (usb_ep_queue(ep, prm->ureq[i].req, GFP_ATOMIC))
 423                         dev_err(dev, "%s:%d Error!\n", __func__, __LINE__);
 424         }
 425
 426         return 0;
 427 }
 428 EXPORT_SYMBOL_GPL(u_audio_start_capture);
 429
 430 void u_audio_stop_capture(struct g_audio *audio_dev)
 431 {
 432         struct snd_uac_chip *uac = audio_dev->uac;
 433
 434         free_ep(&uac->c_prm, audio_dev->out_ep);
 435 }
 436 EXPORT_SYMBOL_GPL(u_audio_stop_capture);
 437
 438 int u_audio_start_playback(struct g_audio *audio_dev)
 439 {
 440         struct snd_uac_chip *uac = audio_dev->uac;
 441         struct usb_gadget *gadget = audio_dev->gadget;
 442         struct device *dev = &gadget->dev;
 443         struct usb_request *req;
 444         struct usb_ep *ep;
 445         struct uac_rtd_params *prm;
 446         struct uac_params *params = &audio_dev->params;
 447         unsigned int factor, rate;
 448         const struct usb_endpoint_descriptor *ep_desc;
 449         int req_len, i;
 450
 451         ep = audio_dev->in_ep;
 452         prm = &uac->p_prm;
 453         config_ep_by_speed(gadget, &audio_dev->func, ep);
 454
 455         ep_desc = ep->desc;
 456
 457         /* pre-calculate the playback endpoint's interval */
 458         if (gadget->speed == USB_SPEED_FULL)
 459                 factor = 1000;
 460         else
 461                 factor = 8000;
 462
 463         /* pre-compute some values for iso_complete() */
 464         uac->p_framesize = params->p_ssize *
 465                             num_channels(params->p_chmask);
 466         rate = params->p_srate * uac->p_framesize;
 467         uac->p_interval = factor / (1 << (ep_desc->bInterval - 1));
 468         uac->p_pktsize = min_t(unsigned int, rate / uac->p_interval,
 469                                 prm->max_psize);
 470
 471         if (uac->p_pktsize < prm->max_psize)
 472                 uac->p_pktsize_residue = rate % uac->p_interval;
 473         else
 474                 uac->p_pktsize_residue = 0;
 475
 476         req_len = uac->p_pktsize;
 477         uac->p_residue = 0;
 478
 479         prm->ep_enabled = true;
 480         usb_ep_enable(ep);
 481
 482         for (i = 0; i < params->req_number; i++) {
 483                 if (!prm->ureq[i].req) {
 484                         req = usb_ep_alloc_request(ep, GFP_ATOMIC);
 485                         if (req == NULL)
 486                                 return -ENOMEM;
 487
 488                         prm->ureq[i].req = req;
 489                         prm->ureq[i].pp = prm;
 490
 491                         req->zero = 0;
 492                         req->context = &prm->ureq[i];
 493                         req->length = req_len;
 494                         req->complete = u_audio_iso_complete;
 495                         req->buf = prm->rbuf + i * prm->max_psize;
 496                 }
 497
 498                 if (usb_ep_queue(ep, prm->ureq[i].req, GFP_ATOMIC))
 499                         dev_err(dev, "%s:%d Error!\n", __func__, __LINE__);
 500         }
 501
 502         return 0;
 503 }
 504 EXPORT_SYMBOL_GPL(u_audio_start_playback);
 505
 506 void u_audio_stop_playback(struct g_audio *audio_dev)
 507 {
 508         struct snd_uac_chip *uac = audio_dev->uac;
 509
 510         free_ep(&uac->p_prm, audio_dev->in_ep);
 511 }
 512 EXPORT_SYMBOL_GPL(u_audio_stop_playback);
 513
 514 int g_audio_setup(struct g_audio *g_audio, const char *pcm_name,
 515                                         const char *card_name)
 516 {
 517         struct snd_uac_chip *uac;
 518         struct snd_card *card;
 519         struct snd_pcm *pcm;
 520         struct uac_params *params;
 521         int p_chmask, c_chmask;
 522         int err;
 523
 524         if (!g_audio)
 525                 return -EINVAL;
 526
 527         uac = kzalloc(sizeof(*uac), GFP_KERNEL);
 528         if (!uac)
 529                 return -ENOMEM;
 530         g_audio->uac = uac;
 531         uac->audio_dev = g_audio;
 532
 533         params = &g_audio->params;
 534         p_chmask = params->p_chmask;
 535         c_chmask = params->c_chmask;
 536
 537         if (c_chmask) {
 538                 struct uac_rtd_params *prm = &uac->c_prm;
 539
 540                 uac->c_prm.uac = uac;
 541                 prm->max_psize = g_audio->out_ep_maxpsize;
 542
 543                 prm->ureq = kcalloc(params->req_number, sizeof(struct uac_req),
 544                                 GFP_KERNEL);
 545                 if (!prm->ureq) {
 546                         err = -ENOMEM;
 547                         goto fail;
 548                 }
 549
 550                 prm->rbuf = kcalloc(params->req_number, prm->max_psize,
 551                                 GFP_KERNEL);
 552                 if (!prm->rbuf) {
 553                         prm->max_psize = 0;
 554                         err = -ENOMEM;
 555                         goto fail;
 556                 }
 557         }
 558
 559         if (p_chmask) {
 560                 struct uac_rtd_params *prm = &uac->p_prm;
 561
 562                 uac->p_prm.uac = uac;
 563                 prm->max_psize = g_audio->in_ep_maxpsize;
 564
 565                 prm->ureq = kcalloc(params->req_number, sizeof(struct uac_req),
 566                                 GFP_KERNEL);
 567                 if (!prm->ureq) {
 568                         err = -ENOMEM;
 569                         goto fail;
 570                 }
 571
 572                 prm->rbuf = kcalloc(params->req_number, prm->max_psize,
 573                                 GFP_KERNEL);
 574                 if (!prm->rbuf) {
 575                         prm->max_psize = 0;
 576                         err = -ENOMEM;
 577                         goto fail;
 578                 }
 579         }
 580
 581         /* Choose any slot, with no id */
 582         err = snd_card_new(&g_audio->gadget->dev,
 583                         -1, NULL, THIS_MODULE, 0, &card);
 584         if (err < 0)
 585                 goto fail;
 586
 587         uac->card = card;
 588
 589         /*
 590          * Create first PCM device
 591          * Create a substream only for non-zero channel streams
 592          */
 593         err = snd_pcm_new(uac->card, pcm_name, 0,
 594                                p_chmask ? 1 : 0, c_chmask ? 1 : 0, &pcm);
 595         if (err < 0)
 596                 goto snd_fail;
 597
 598         strcpy(pcm->name, pcm_name);
 599         pcm->private_data = uac;
 600         uac->pcm = pcm;
 601
 602         snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK, &uac_pcm_ops);
 603         snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_CAPTURE, &uac_pcm_ops);
 604
 605         strcpy(card->driver, card_name);
 606         strcpy(card->shortname, card_name);
 607         sprintf(card->longname, "%s %i", card_name, card->dev->id);
 608
 609         snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_CONTINUOUS,
 610                 snd_dma_continuous_data(GFP_KERNEL), 0, BUFF_SIZE_MAX);
 611
 612         err = snd_card_register(card);
 613
 614         if (!err)
 615                 return 0;
 616
 617 snd_fail:
 618         snd_card_free(card);
 619 fail:
 620         kfree(uac->p_prm.ureq);
 621         kfree(uac->c_prm.ureq);
 622         kfree(uac->p_prm.rbuf);
 623         kfree(uac->c_prm.rbuf);
 624         kfree(uac);
 625
 626         return err;
 627 }
 628 EXPORT_SYMBOL_GPL(g_audio_setup);
 629
 630 void g_audio_cleanup(struct g_audio *g_audio)
 631 {
 632         struct snd_uac_chip *uac;
 633         struct snd_card *card;
 634
 635         if (!g_audio || !g_audio->uac)
 636                 return;
 637
 638         uac = g_audio->uac;
 639         card = uac->card;
 640         if (card)
 641                 snd_card_free(card);
 642
 643         kfree(uac->p_prm.ureq);
 644         kfree(uac->c_prm.ureq);
 645         kfree(uac->p_prm.rbuf);
 646         kfree(uac->c_prm.rbuf);
 647         kfree(uac);
 648 }
 649 EXPORT_SYMBOL_GPL(g_audio_cleanup);
 650
 651 MODULE_LICENSE("GPL");
 652 MODULE_DESCRIPTION("USB gadget \"ALSA sound card\" utilities");
 653 MODULE_AUTHOR("Ruslan Bilovol");