drivers/usb/core/devices.c

   1 // SPDX-License-Identifier: GPL-2.0+
   2 /*
   3  * devices.c
   4  * (C) Copyright 1999 Randy Dunlap.
   5  * (C) Copyright 1999,2000 Thomas Sailer <sailer@ife.ee.ethz.ch>.
   6  *     (proc file per device)
   7  * (C) Copyright 1999 Deti Fliegl (new USB architecture)
   8  *
   9  *************************************************************
  10  *
  11  * <mountpoint>/devices contains USB topology, device, config, class,
  12  * interface, & endpoint data.
  13  *
  14  * I considered using /dev/bus/usb/device# for each device
  15  * as it is attached or detached, but I didn't like this for some
  16  * reason -- maybe it's just too deep of a directory structure.
  17  * I also don't like looking in multiple places to gather and view
  18  * the data.  Having only one file for ./devices also prevents race
  19  * conditions that could arise if a program was reading device info
  20  * for devices that are being removed (unplugged).  (That is, the
  21  * program may find a directory for devnum_12 then try to open it,
  22  * but it was just unplugged, so the directory is now deleted.
  23  * But programs would just have to be prepared for situations like
  24  * this in any plug-and-play environment.)
  25  *
  26  * 1999-12-16: Thomas Sailer <sailer@ife.ee.ethz.ch>
  27  *   Converted the whole proc stuff to real
  28  *   read methods. Now not the whole device list needs to fit
  29  *   into one page, only the device list for one bus.
  30  *   Added a poll method to /sys/kernel/debug/usb/devices, to wake
  31  *   up an eventual usbd
  32  * 2000-01-04: Thomas Sailer <sailer@ife.ee.ethz.ch>
  33  *   Turned into its own filesystem
  34  * 2000-07-05: Ashley Montanaro <ashley@compsoc.man.ac.uk>
  35  *   Converted file reading routine to dump to buffer once
  36  *   per device, not per bus
  37  */
  38
  39 #include <linux/fs.h>
  40 #include <linux/mm.h>
  41 #include <linux/gfp.h>
  42 #include <linux/poll.h>
  43 #include <linux/usb.h>
  44 #include <linux/usbdevice_fs.h>
  45 #include <linux/usb/hcd.h>
  46 #include <linux/mutex.h>
  47 #include <linux/uaccess.h>
  48
  49 #include "usb.h"
  50
  51 /* Define ALLOW_SERIAL_NUMBER if you want to see the serial number of devices */
  52 #define ALLOW_SERIAL_NUMBER
  53
  54 static const char format_topo[] =
  55 /* T:  Bus=dd Lev=dd Prnt=dd Port=dd Cnt=dd Dev#=ddd Spd=dddd MxCh=dd */
  56 "\nT:  Bus=%2.2d Lev=%2.2d Prnt=%2.2d Port=%2.2d Cnt=%2.2d Dev#=%3d Spd=%-4s MxCh=%2d\n";
  57
  58 static const char format_string_manufacturer[] =
  59 /* S:  Manufacturer=xxxx */
  60   "S:  Manufacturer=%.100s\n";
  61
  62 static const char format_string_product[] =
  63 /* S:  Product=xxxx */
  64   "S:  Product=%.100s\n";
  65
  66 #ifdef ALLOW_SERIAL_NUMBER
  67 static const char format_string_serialnumber[] =
  68 /* S:  SerialNumber=xxxx */
  69   "S:  SerialNumber=%.100s\n";
  70 #endif
  71
  72 static const char format_bandwidth[] =
  73 /* B:  Alloc=ddd/ddd us (xx%), #Int=ddd, #Iso=ddd */
  74   "B:  Alloc=%3d/%3d us (%2d%%), #Int=%3d, #Iso=%3d\n";
  75
  76 static const char format_device1[] =
  77 /* D:  Ver=xx.xx Cls=xx(sssss) Sub=xx Prot=xx MxPS=dd #Cfgs=dd */
  78   "D:  Ver=%2x.%02x Cls=%02x(%-5s) Sub=%02x Prot=%02x MxPS=%2d #Cfgs=%3d\n";
  79
  80 static const char format_device2[] =
  81 /* P:  Vendor=xxxx ProdID=xxxx Rev=xx.xx */
  82   "P:  Vendor=%04x ProdID=%04x Rev=%2x.%02x\n";
  83
  84 static const char format_config[] =
  85 /* C:  #Ifs=dd Cfg#=dd Atr=xx MPwr=dddmA */
  86   "C:%c #Ifs=%2d Cfg#=%2d Atr=%02x MxPwr=%3dmA\n";
  87
  88 static const char format_iad[] =
  89 /* A:  FirstIf#=dd IfCount=dd Cls=xx(sssss) Sub=xx Prot=xx */
  90   "A:  FirstIf#=%2d IfCount=%2d Cls=%02x(%-5s) Sub=%02x Prot=%02x\n";
  91
  92 static const char format_iface[] =
  93 /* I:  If#=dd Alt=dd #EPs=dd Cls=xx(sssss) Sub=xx Prot=xx Driver=xxxx*/
  94   "I:%c If#=%2d Alt=%2d #EPs=%2d Cls=%02x(%-5s) Sub=%02x Prot=%02x Driver=%s\n";
  95
  96 static const char format_endpt[] =
  97 /* E:  Ad=xx(s) Atr=xx(ssss) MxPS=dddd Ivl=D?s */
  98   "E:  Ad=%02x(%c) Atr=%02x(%-4s) MxPS=%4d Ivl=%d%cs\n";
  99
 100 /*
 101  * Wait for an connect/disconnect event to happen. We initialize
 102  * the event counter with an odd number, and each event will increment
 103  * the event counter by two, so it will always _stay_ odd. That means
 104  * that it will never be zero, so "event 0" will never match a current
 105  * event, and thus 'poll' will always trigger as readable for the first
 106  * time it gets called.
 107  */
 108 static struct device_connect_event {
 109         atomic_t count;
 110         wait_queue_head_t wait;
 111 } device_event = {
 112         .count = ATOMIC_INIT(1),
 113         .wait = __WAIT_QUEUE_HEAD_INITIALIZER(device_event.wait)
 114 };
 115
 116 struct class_info {
 117         int class;
 118         char *class_name;
 119 };
 120
 121 static const struct class_info clas_info[] = {
 122         /* max. 5 chars. per name string */
 123         {USB_CLASS_PER_INTERFACE,       ">ifc"},
 124         {USB_CLASS_AUDIO,               "audio"},
 125         {USB_CLASS_COMM,                "comm."},
 126         {USB_CLASS_HID,                 "HID"},
 127         {USB_CLASS_PHYSICAL,            "PID"},
 128         {USB_CLASS_STILL_IMAGE,         "still"},
 129         {USB_CLASS_PRINTER,             "print"},
 130         {USB_CLASS_MASS_STORAGE,        "stor."},
 131         {USB_CLASS_HUB,                 "hub"},
 132         {USB_CLASS_CDC_DATA,            "data"},
 133         {USB_CLASS_CSCID,               "scard"},
 134         {USB_CLASS_CONTENT_SEC,         "c-sec"},
 135         {USB_CLASS_VIDEO,               "video"},
 136         {USB_CLASS_WIRELESS_CONTROLLER, "wlcon"},
 137         {USB_CLASS_MISC,                "misc"},
 138         {USB_CLASS_APP_SPEC,            "app."},
 139         {USB_CLASS_VENDOR_SPEC,         "vend."},
 140         {-1,                            "unk."}         /* leave as last */
 141 };
 142
 143 /*****************************************************************/
 144
 145 void usbfs_conn_disc_event(void)
 146 {
 147         atomic_add(2, &device_event.count);
 148         wake_up(&device_event.wait);
 149 }
 150
 151 static const char *class_decode(const int class)
 152 {
 153         int ix;
 154
 155         for (ix = 0; clas_info[ix].class != -1; ix++)
 156                 if (clas_info[ix].class == class)
 157                         break;
 158         return clas_info[ix].class_name;
 159 }
 160
 161 static char *usb_dump_endpoint_descriptor(int speed, char *start, char *end,
 162                                 const struct usb_endpoint_descriptor *desc)
 163 {
 164         char dir, unit, *type;
 165         unsigned interval, bandwidth = 1;
 166
 167         if (start > end)
 168                 return start;
 169
 170         dir = usb_endpoint_dir_in(desc) ? 'I' : 'O';
 171
 172         if (speed == USB_SPEED_HIGH)
 173                 bandwidth = usb_endpoint_maxp_mult(desc);
 174
 175         /* this isn't checking for illegal values */
 176         switch (usb_endpoint_type(desc)) {
 177         case USB_ENDPOINT_XFER_CONTROL:
 178                 type = "Ctrl";
 179                 if (speed == USB_SPEED_HIGH)    /* uframes per NAK */
 180                         interval = desc->bInterval;
 181                 else
 182                         interval = 0;
 183                 dir = 'B';                      /* ctrl is bidirectional */
 184                 break;
 185         case USB_ENDPOINT_XFER_ISOC:
 186                 type = "Isoc";
 187                 interval = 1 << (desc->bInterval - 1);
 188                 break;
 189         case USB_ENDPOINT_XFER_BULK:
 190                 type = "Bulk";
 191                 if (speed == USB_SPEED_HIGH && dir == 'O') /* uframes per NAK */
 192                         interval = desc->bInterval;
 193                 else
 194                         interval = 0;
 195                 break;
 196         case USB_ENDPOINT_XFER_INT:
 197                 type = "Int.";
 198                 if (speed == USB_SPEED_HIGH || speed >= USB_SPEED_SUPER)
 199                         interval = 1 << (desc->bInterval - 1);
 200                 else
 201                         interval = desc->bInterval;
 202                 break;
 203         default:        /* "can't happen" */
 204                 return start;
 205         }
 206         interval *= (speed == USB_SPEED_HIGH ||
 207                      speed >= USB_SPEED_SUPER) ? 125 : 1000;
 208         if (interval % 1000)
 209                 unit = 'u';
 210         else {
 211                 unit = 'm';
 212                 interval /= 1000;
 213         }
 214
 215         start += sprintf(start, format_endpt, desc->bEndpointAddress, dir,
 216                          desc->bmAttributes, type,
 217                          usb_endpoint_maxp(desc) *
 218                          bandwidth,
 219                          interval, unit);
 220         return start;
 221 }
 222
 223 static char *usb_dump_interface_descriptor(char *start, char *end,
 224                                         const struct usb_interface_cache *intfc,
 225                                         const struct usb_interface *iface,
 226                                         int setno)
 227 {
 228         const struct usb_interface_descriptor *desc;
 229         const char *driver_name = "";
 230         int active = 0;
 231
 232         if (start > end)
 233                 return start;
 234         desc = &intfc->altsetting[setno].desc;
 235         if (iface) {
 236                 driver_name = (iface->dev.driver
 237                                 ? iface->dev.driver->name
 238                                 : "(none)");
 239                 active = (desc == &iface->cur_altsetting->desc);
 240         }
 241         start += sprintf(start, format_iface,
 242                          active ? '*' : ' ',    /* mark active altsetting */
 243                          desc->bInterfaceNumber,
 244                          desc->bAlternateSetting,
 245                          desc->bNumEndpoints,
 246                          desc->bInterfaceClass,
 247                          class_decode(desc->bInterfaceClass),
 248                          desc->bInterfaceSubClass,
 249                          desc->bInterfaceProtocol,
 250                          driver_name);
 251         return start;
 252 }
 253
 254 static char *usb_dump_interface(int speed, char *start, char *end,
 255                                 const struct usb_interface_cache *intfc,
 256                                 const struct usb_interface *iface, int setno)
 257 {
 258         const struct usb_host_interface *desc = &intfc->altsetting[setno];
 259         int i;
 260
 261         start = usb_dump_interface_descriptor(start, end, intfc, iface, setno);
 262         for (i = 0; i < desc->desc.bNumEndpoints; i++) {
 263                 if (start > end)
 264                         return start;
 265                 start = usb_dump_endpoint_descriptor(speed,
 266                                 start, end, &desc->endpoint[i].desc);
 267         }
 268         return start;
 269 }
 270
 271 static char *usb_dump_iad_descriptor(char *start, char *end,
 272                         const struct usb_interface_assoc_descriptor *iad)
 273 {
 274         if (start > end)
 275                 return start;
 276         start += sprintf(start, format_iad,
 277                          iad->bFirstInterface,
 278                          iad->bInterfaceCount,
 279                          iad->bFunctionClass,
 280                          class_decode(iad->bFunctionClass),
 281                          iad->bFunctionSubClass,
 282                          iad->bFunctionProtocol);
 283         return start;
 284 }
 285
 286 /* TBD:
 287  * 0. TBDs
 288  * 1. marking active interface altsettings (code lists all, but should mark
 289  *    which ones are active, if any)
 290  */
 291 static char *usb_dump_config_descriptor(char *start, char *end,
 292                                 const struct usb_config_descriptor *desc,
 293                                 int active, int speed)
 294 {
 295         int mul;
 296
 297         if (start > end)
 298                 return start;
 299         if (speed >= USB_SPEED_SUPER)
 300                 mul = 8;
 301         else
 302                 mul = 2;
 303         start += sprintf(start, format_config,
 304                          /* mark active/actual/current cfg. */
 305                          active ? '*' : ' ',
 306                          desc->bNumInterfaces,
 307                          desc->bConfigurationValue,
 308                          desc->bmAttributes,
 309                          desc->bMaxPower * mul);
 310         return start;
 311 }
 312
 313 static char *usb_dump_config(int speed, char *start, char *end,
 314                              const struct usb_host_config *config, int active)
 315 {
 316         int i, j;
 317         struct usb_interface_cache *intfc;
 318         struct usb_interface *interface;
 319
 320         if (start > end)
 321                 return start;
 322         if (!config)
 323                 /* getting these some in 2.3.7; none in 2.3.6 */
 324                 return start + sprintf(start, "(null Cfg. desc.)\n");
 325         start = usb_dump_config_descriptor(start, end, &config->desc, active,
 326                         speed);
 327         for (i = 0; i < USB_MAXIADS; i++) {
 328                 if (config->intf_assoc[i] == NULL)
 329                         break;
 330                 start = usb_dump_iad_descriptor(start, end,
 331                                         config->intf_assoc[i]);
 332         }
 333         for (i = 0; i < config->desc.bNumInterfaces; i++) {
 334                 intfc = config->intf_cache[i];
 335                 interface = config->interface[i];
 336                 for (j = 0; j < intfc->num_altsetting; j++) {
 337                         if (start > end)
 338                                 return start;
 339                         start = usb_dump_interface(speed,
 340                                 start, end, intfc, interface, j);
 341                 }
 342         }
 343         return start;
 344 }
 345
 346 /*
 347  * Dump the different USB descriptors.
 348  */
 349 static char *usb_dump_device_descriptor(char *start, char *end,
 350                                 const struct usb_device_descriptor *desc)
 351 {
 352         u16 bcdUSB = le16_to_cpu(desc->bcdUSB);
 353         u16 bcdDevice = le16_to_cpu(desc->bcdDevice);
 354
 355         if (start > end)
 356                 return start;
 357         start += sprintf(start, format_device1,
 358                           bcdUSB >> 8, bcdUSB & 0xff,
 359                           desc->bDeviceClass,
 360                           class_decode(desc->bDeviceClass),
 361                           desc->bDeviceSubClass,
 362                           desc->bDeviceProtocol,
 363                           desc->bMaxPacketSize0,
 364                           desc->bNumConfigurations);
 365         if (start > end)
 366                 return start;
 367         start += sprintf(start, format_device2,
 368                          le16_to_cpu(desc->idVendor),
 369                          le16_to_cpu(desc->idProduct),
 370                          bcdDevice >> 8, bcdDevice & 0xff);
 371         return start;
 372 }
 373
 374 /*
 375  * Dump the different strings that this device holds.
 376  */
 377 static char *usb_dump_device_strings(char *start, char *end,
 378                                      struct usb_device *dev)
 379 {
 380         if (start > end)
 381                 return start;
 382         if (dev->manufacturer)
 383                 start += sprintf(start, format_string_manufacturer,
 384                                  dev->manufacturer);
 385         if (start > end)
 386                 goto out;
 387         if (dev->product)
 388                 start += sprintf(start, format_string_product, dev->product);
 389         if (start > end)
 390                 goto out;
 391 #ifdef ALLOW_SERIAL_NUMBER
 392         if (dev->serial)
 393                 start += sprintf(start, format_string_serialnumber,
 394                                  dev->serial);
 395 #endif
 396  out:
 397         return start;
 398 }
 399
 400 static char *usb_dump_desc(char *start, char *end, struct usb_device *dev)
 401 {
 402         int i;
 403
 404         if (start > end)
 405                 return start;
 406
 407         start = usb_dump_device_descriptor(start, end, &dev->descriptor);
 408
 409         if (start > end)
 410                 return start;
 411
 412         start = usb_dump_device_strings(start, end, dev);
 413
 414         for (i = 0; i < dev->descriptor.bNumConfigurations; i++) {
 415                 if (start > end)
 416                         return start;
 417                 start = usb_dump_config(dev->speed,
 418                                 start, end, dev->config + i,
 419                                 /* active ? */
 420                                 (dev->config + i) == dev->actconfig);
 421         }
 422         return start;
 423 }
 424
 425
 426 #ifdef PROC_EXTRA /* TBD: may want to add this code later */
 427
 428 static char *usb_dump_hub_descriptor(char *start, char *end,
 429                                      const struct usb_hub_descriptor *desc)
 430 {
 431         int leng = USB_DT_HUB_NONVAR_SIZE;
 432         unsigned char *ptr = (unsigned char *)desc;
 433
 434         if (start > end)
 435                 return start;
 436         start += sprintf(start, "Interface:");
 437         while (leng && start <= end) {
 438                 start += sprintf(start, " %02x", *ptr);
 439                 ptr++; leng--;
 440         }
 441         *start++ = '\n';
 442         return start;
 443 }
 444
 445 static char *usb_dump_string(char *start, char *end,
 446                              const struct usb_device *dev, char *id, int index)
 447 {
 448         if (start > end)
 449                 return start;
 450         start += sprintf(start, "Interface:");
 451         if (index <= dev->maxstring && dev->stringindex &&
 452             dev->stringindex[index])
 453                 start += sprintf(start, "%s: %.100s ", id,
 454                                  dev->stringindex[index]);
 455         return start;
 456 }
 457
 458 #endif /* PROC_EXTRA */
 459
 460 /*****************************************************************/
 461
 462 /* This is a recursive function. Parameters:
 463  * buffer - the user-space buffer to write data into
 464  * nbytes - the maximum number of bytes to write
 465  * skip_bytes - the number of bytes to skip before writing anything
 466  * file_offset - the offset into the devices file on completion
 467  * The caller must own the device lock.
 468  */
 469 static ssize_t usb_device_dump(char __user **buffer, size_t *nbytes,
 470                                loff_t *skip_bytes, loff_t *file_offset,
 471                                struct usb_device *usbdev, struct usb_bus *bus,
 472                                int level, int index, int count)
 473 {
 474         int chix;
 475         int ret, cnt = 0;
 476         int parent_devnum = 0;
 477         char *pages_start, *data_end, *speed;
 478         unsigned int length;
 479         ssize_t total_written = 0;
 480         struct usb_device *childdev = NULL;
 481
 482         /* don't bother with anything else if we're not writing any data */
 483         if (*nbytes <= 0)
 484                 return 0;
 485
 486         if (level > MAX_TOPO_LEVEL)
 487                 return 0;
 488         /* allocate 2^1 pages = 8K (on i386);
 489          * should be more than enough for one device */
 490         pages_start = (char *)__get_free_pages(GFP_NOIO, 1);
 491         if (!pages_start)
 492                 return -ENOMEM;
 493
 494         if (usbdev->parent && usbdev->parent->devnum != -1)
 495                 parent_devnum = usbdev->parent->devnum;
 496         /*
 497          * So the root hub's parent is 0 and any device that is
 498          * plugged into the root hub has a parent of 0.
 499          */
 500         switch (usbdev->speed) {
 501         case USB_SPEED_LOW:
 502                 speed = "1.5"; break;
 503         case USB_SPEED_UNKNOWN:         /* usb 1.1 root hub code */
 504         case USB_SPEED_FULL:
 505                 speed = "12"; break;
 506         case USB_SPEED_WIRELESS:        /* Wireless has no real fixed speed */
 507         case USB_SPEED_HIGH:
 508                 speed = "480"; break;
 509         case USB_SPEED_SUPER:
 510                 speed = "5000"; break;
 511         case USB_SPEED_SUPER_PLUS:
 512                 speed = "10000"; break;
 513         default:
 514                 speed = "??";
 515         }
 516         data_end = pages_start + sprintf(pages_start, format_topo,
 517                         bus->busnum, level, parent_devnum,
 518                         index, count, usbdev->devnum,
 519                         speed, usbdev->maxchild);
 520         /*
 521          * level = topology-tier level;
 522          * parent_devnum = parent device number;
 523          * index = parent's connector number;
 524          * count = device count at this level
 525          */
 526         /* If this is the root hub, display the bandwidth information */
 527         if (level == 0) {
 528                 int     max;
 529
 530                 /* super/high speed reserves 80%, full/low reserves 90% */
 531                 if (usbdev->speed == USB_SPEED_HIGH ||
 532                     usbdev->speed >= USB_SPEED_SUPER)
 533                         max = 800;
 534                 else
 535                         max = FRAME_TIME_MAX_USECS_ALLOC;
 536
 537                 /* report "average" periodic allocation over a microsecond.
 538                  * the schedules are actually bursty, HCDs need to deal with
 539                  * that and just compute/report this average.
 540                  */
 541                 data_end += sprintf(data_end, format_bandwidth,
 542                                 bus->bandwidth_allocated, max,
 543                                 (100 * bus->bandwidth_allocated + max / 2)
 544                                         / max,
 545                                 bus->bandwidth_int_reqs,
 546                                 bus->bandwidth_isoc_reqs);
 547
 548         }
 549         data_end = usb_dump_desc(data_end, pages_start + (2 * PAGE_SIZE) - 256,
 550                                  usbdev);
 551
 552         if (data_end > (pages_start + (2 * PAGE_SIZE) - 256))
 553                 data_end += sprintf(data_end, "(truncated)\n");
 554
 555         length = data_end - pages_start;
 556         /* if we can start copying some data to the user */
 557         if (length > *skip_bytes) {
 558                 length -= *skip_bytes;
 559                 if (length > *nbytes)
 560                         length = *nbytes;
 561                 if (copy_to_user(*buffer, pages_start + *skip_bytes, length)) {
 562                         free_pages((unsigned long)pages_start, 1);
 563                         return -EFAULT;
 564                 }
 565                 *nbytes -= length;
 566                 *file_offset += length;
 567                 total_written += length;
 568                 *buffer += length;
 569                 *skip_bytes = 0;
 570         } else
 571                 *skip_bytes -= length;
 572
 573         free_pages((unsigned long)pages_start, 1);
 574
 575         /* Now look at all of this device's children. */
 576         usb_hub_for_each_child(usbdev, chix, childdev) {
 577                 usb_lock_device(childdev);
 578                 ret = usb_device_dump(buffer, nbytes, skip_bytes,
 579                                       file_offset, childdev, bus,
 580                                       level + 1, chix - 1, ++cnt);
 581                 usb_unlock_device(childdev);
 582                 if (ret == -EFAULT)
 583                         return total_written;
 584                 total_written += ret;
 585         }
 586         return total_written;
 587 }
 588
 589 static ssize_t usb_device_read(struct file *file, char __user *buf,
 590                                size_t nbytes, loff_t *ppos)
 591 {
 592         struct usb_bus *bus;
 593         ssize_t ret, total_written = 0;
 594         loff_t skip_bytes = *ppos;
 595         int id;
 596
 597         if (*ppos < 0)
 598                 return -EINVAL;
 599         if (nbytes <= 0)
 600                 return 0;
 601         if (!access_ok(buf, nbytes))
 602                 return -EFAULT;
 603
 604         mutex_lock(&usb_bus_idr_lock);
 605         /* print devices for all busses */
 606         idr_for_each_entry(&usb_bus_idr, bus, id) {
 607                 /* recurse through all children of the root hub */
 608                 if (!bus_to_hcd(bus)->rh_registered)
 609                         continue;
 610                 usb_lock_device(bus->root_hub);
 611                 ret = usb_device_dump(&buf, &nbytes, &skip_bytes, ppos,
 612                                       bus->root_hub, bus, 0, 0, 0);
 613                 usb_unlock_device(bus->root_hub);
 614                 if (ret < 0) {
 615                         mutex_unlock(&usb_bus_idr_lock);
 616                         return ret;
 617                 }
 618                 total_written += ret;
 619         }
 620         mutex_unlock(&usb_bus_idr_lock);
 621         return total_written;
 622 }
 623
 624 /* Kernel lock for "lastev" protection */
 625 static __poll_t usb_device_poll(struct file *file,
 626                                     struct poll_table_struct *wait)
 627 {
 628         unsigned int event_count;
 629
 630         poll_wait(file, &device_event.wait, wait);
 631
 632         event_count = atomic_read(&device_event.count);
 633         if (file->f_version != event_count) {
 634                 file->f_version = event_count;
 635                 return EPOLLIN | EPOLLRDNORM;
 636         }
 637
 638         return 0;
 639 }
 640
 641 const struct file_operations usbfs_devices_fops = {
 642         .llseek =       no_seek_end_llseek,
 643         .read =         usb_device_read,
 644         .poll =         usb_device_poll,
 645 };