drivers/uwb/beacon.c

   1 /*
   2  * Ultra Wide Band
   3  * Beacon management
   4  *
   5  * Copyright (C) 2005-2006 Intel Corporation
   6  * Inaky Perez-Gonzalez <inaky.perez-gonzalez@intel.com>
   7  *
   8  * This program is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU General Public License version
  10  * 2 as published by the Free Software Foundation.
  11  *
  12  * This program is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15  * GNU General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU General Public License
  18  * along with this program; if not, write to the Free Software
  19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  20  * 02110-1301, USA.
  21  *
  22  *
  23  * FIXME: docs
  24  */
  25 #include <linux/kernel.h>
  26 #include <linux/init.h>
  27 #include <linux/module.h>
  28 #include <linux/device.h>
  29 #include <linux/err.h>
  30 #include <linux/kdev_t.h>
  31 #include <linux/slab.h>
  32
  33 #include "uwb-internal.h"
  34
  35 /* Start Beaconing command structure */
  36 struct uwb_rc_cmd_start_beacon {
  37         struct uwb_rccb rccb;
  38         __le16 wBPSTOffset;
  39         u8 bChannelNumber;
  40 } __attribute__((packed));
  41
  42
  43 static int uwb_rc_start_beacon(struct uwb_rc *rc, u16 bpst_offset, u8 channel)
  44 {
  45         int result;
  46         struct uwb_rc_cmd_start_beacon *cmd;
  47         struct uwb_rc_evt_confirm reply;
  48
  49         cmd = kzalloc(sizeof(*cmd), GFP_KERNEL);
  50         if (cmd == NULL)
  51                 return -ENOMEM;
  52         cmd->rccb.bCommandType = UWB_RC_CET_GENERAL;
  53         cmd->rccb.wCommand = cpu_to_le16(UWB_RC_CMD_START_BEACON);
  54         cmd->wBPSTOffset = cpu_to_le16(bpst_offset);
  55         cmd->bChannelNumber = channel;
  56         reply.rceb.bEventType = UWB_RC_CET_GENERAL;
  57         reply.rceb.wEvent = UWB_RC_CMD_START_BEACON;
  58         result = uwb_rc_cmd(rc, "START-BEACON", &cmd->rccb, sizeof(*cmd),
  59                             &reply.rceb, sizeof(reply));
  60         if (result < 0)
  61                 goto error_cmd;
  62         if (reply.bResultCode != UWB_RC_RES_SUCCESS) {
  63                 dev_err(&rc->uwb_dev.dev,
  64                         "START-BEACON: command execution failed: %s (%d)\n",
  65                         uwb_rc_strerror(reply.bResultCode), reply.bResultCode);
  66                 result = -EIO;
  67         }
  68 error_cmd:
  69         kfree(cmd);
  70         return result;
  71 }
  72
  73 static int uwb_rc_stop_beacon(struct uwb_rc *rc)
  74 {
  75         int result;
  76         struct uwb_rccb *cmd;
  77         struct uwb_rc_evt_confirm reply;
  78
  79         cmd = kzalloc(sizeof(*cmd), GFP_KERNEL);
  80         if (cmd == NULL)
  81                 return -ENOMEM;
  82         cmd->bCommandType = UWB_RC_CET_GENERAL;
  83         cmd->wCommand = cpu_to_le16(UWB_RC_CMD_STOP_BEACON);
  84         reply.rceb.bEventType = UWB_RC_CET_GENERAL;
  85         reply.rceb.wEvent = UWB_RC_CMD_STOP_BEACON;
  86         result = uwb_rc_cmd(rc, "STOP-BEACON", cmd, sizeof(*cmd),
  87                             &reply.rceb, sizeof(reply));
  88         if (result < 0)
  89                 goto error_cmd;
  90         if (reply.bResultCode != UWB_RC_RES_SUCCESS) {
  91                 dev_err(&rc->uwb_dev.dev,
  92                         "STOP-BEACON: command execution failed: %s (%d)\n",
  93                         uwb_rc_strerror(reply.bResultCode), reply.bResultCode);
  94                 result = -EIO;
  95         }
  96 error_cmd:
  97         kfree(cmd);
  98         return result;
  99 }
 100
 101 /*
 102  * Start/stop beacons
 103  *
 104  * @rc:          UWB Radio Controller to operate on
 105  * @channel:     UWB channel on which to beacon (WUSB[table
 106  *               5-12]). If -1, stop beaconing.
 107  * @bpst_offset: Beacon Period Start Time offset; FIXME-do zero
 108  *
 109  * According to WHCI 0.95 [4.13.6] the driver will only receive the RCEB
 110  * of a SET IE command after the device sent the first beacon that includes
 111  * the IEs specified in the SET IE command. So, after we start beaconing we
 112  * check if there is anything in the IE cache and call the SET IE command
 113  * if needed.
 114  */
 115 int uwb_rc_beacon(struct uwb_rc *rc, int channel, unsigned bpst_offset)
 116 {
 117         int result;
 118         struct device *dev = &rc->uwb_dev.dev;
 119
 120         if (channel < 0)
 121                 channel = -1;
 122         if (channel == -1)
 123                 result = uwb_rc_stop_beacon(rc);
 124         else {
 125                 /* channel >= 0...dah */
 126                 result = uwb_rc_start_beacon(rc, bpst_offset, channel);
 127                 if (result < 0)
 128                         return result;
 129                 if (le16_to_cpu(rc->ies->wIELength) > 0) {
 130                         result = uwb_rc_set_ie(rc, rc->ies);
 131                         if (result < 0) {
 132                                 dev_err(dev, "Cannot set new IE on device: "
 133                                         "%d\n", result);
 134                                 result = uwb_rc_stop_beacon(rc);
 135                                 channel = -1;
 136                                 bpst_offset = 0;
 137                         }
 138                 }
 139         }
 140
 141         if (result >= 0)
 142                 rc->beaconing = channel;
 143         return result;
 144 }
 145
 146 /*
 147  * Beacon cache
 148  *
 149  * The purpose of this is to speed up the lookup of becon information
 150  * when a new beacon arrives. The UWB Daemon uses it also to keep a
 151  * tab of which devices are in radio distance and which not. When a
 152  * device's beacon stays present for more than a certain amount of
 153  * time, it is considered a new, usable device. When a beacon ceases
 154  * to be received for a certain amount of time, it is considered that
 155  * the device is gone.
 156  *
 157  * FIXME: use an allocator for the entries
 158  * FIXME: use something faster for search than a list
 159  */
 160
 161 void uwb_bce_kfree(struct kref *_bce)
 162 {
 163         struct uwb_beca_e *bce = container_of(_bce, struct uwb_beca_e, refcnt);
 164
 165         kfree(bce->be);
 166         kfree(bce);
 167 }
 168
 169
 170 /* Find a beacon by dev addr in the cache */
 171 static
 172 struct uwb_beca_e *__uwb_beca_find_bydev(struct uwb_rc *rc,
 173                                          const struct uwb_dev_addr *dev_addr)
 174 {
 175         struct uwb_beca_e *bce, *next;
 176         list_for_each_entry_safe(bce, next, &rc->uwb_beca.list, node) {
 177                 if (!memcmp(&bce->dev_addr, dev_addr, sizeof(bce->dev_addr)))
 178                         goto out;
 179         }
 180         bce = NULL;
 181 out:
 182         return bce;
 183 }
 184
 185 /* Find a beacon by dev addr in the cache */
 186 static
 187 struct uwb_beca_e *__uwb_beca_find_bymac(struct uwb_rc *rc,
 188                                          const struct uwb_mac_addr *mac_addr)
 189 {
 190         struct uwb_beca_e *bce, *next;
 191         list_for_each_entry_safe(bce, next, &rc->uwb_beca.list, node) {
 192                 if (!memcmp(bce->mac_addr, mac_addr->data,
 193                             sizeof(struct uwb_mac_addr)))
 194                         goto out;
 195         }
 196         bce = NULL;
 197 out:
 198         return bce;
 199 }
 200
 201 /**
 202  * uwb_dev_get_by_devaddr - get a UWB device with a specific DevAddr
 203  * @rc:      the radio controller that saw the device
 204  * @devaddr: DevAddr of the UWB device to find
 205  *
 206  * There may be more than one matching device (in the case of a
 207  * DevAddr conflict), but only the first one is returned.
 208  */
 209 struct uwb_dev *uwb_dev_get_by_devaddr(struct uwb_rc *rc,
 210                                        const struct uwb_dev_addr *devaddr)
 211 {
 212         struct uwb_dev *found = NULL;
 213         struct uwb_beca_e *bce;
 214
 215         mutex_lock(&rc->uwb_beca.mutex);
 216         bce = __uwb_beca_find_bydev(rc, devaddr);
 217         if (bce)
 218                 found = uwb_dev_try_get(rc, bce->uwb_dev);
 219         mutex_unlock(&rc->uwb_beca.mutex);
 220
 221         return found;
 222 }
 223
 224 /**
 225  * uwb_dev_get_by_macaddr - get a UWB device with a specific EUI-48
 226  * @rc:      the radio controller that saw the device
 227  * @devaddr: EUI-48 of the UWB device to find
 228  */
 229 struct uwb_dev *uwb_dev_get_by_macaddr(struct uwb_rc *rc,
 230                                        const struct uwb_mac_addr *macaddr)
 231 {
 232         struct uwb_dev *found = NULL;
 233         struct uwb_beca_e *bce;
 234
 235         mutex_lock(&rc->uwb_beca.mutex);
 236         bce = __uwb_beca_find_bymac(rc, macaddr);
 237         if (bce)
 238                 found = uwb_dev_try_get(rc, bce->uwb_dev);
 239         mutex_unlock(&rc->uwb_beca.mutex);
 240
 241         return found;
 242 }
 243
 244 /* Initialize a beacon cache entry */
 245 static void uwb_beca_e_init(struct uwb_beca_e *bce)
 246 {
 247         mutex_init(&bce->mutex);
 248         kref_init(&bce->refcnt);
 249         stats_init(&bce->lqe_stats);
 250         stats_init(&bce->rssi_stats);
 251 }
 252
 253 /*
 254  * Add a beacon to the cache
 255  *
 256  * @be:         Beacon event information
 257  * @bf:         Beacon frame (part of b, really)
 258  * @ts_jiffies: Timestamp (in jiffies) when the beacon was received
 259  */
 260 static
 261 struct uwb_beca_e *__uwb_beca_add(struct uwb_rc *rc,
 262                                   struct uwb_rc_evt_beacon *be,
 263                                   struct uwb_beacon_frame *bf,
 264                                   unsigned long ts_jiffies)
 265 {
 266         struct uwb_beca_e *bce;
 267
 268         bce = kzalloc(sizeof(*bce), GFP_KERNEL);
 269         if (bce == NULL)
 270                 return NULL;
 271         uwb_beca_e_init(bce);
 272         bce->ts_jiffies = ts_jiffies;
 273         bce->uwb_dev = NULL;
 274         list_add(&bce->node, &rc->uwb_beca.list);
 275         return bce;
 276 }
 277
 278 /*
 279  * Wipe out beacon entries that became stale
 280  *
 281  * Remove associated devicest too.
 282  */
 283 void uwb_beca_purge(struct uwb_rc *rc)
 284 {
 285         struct uwb_beca_e *bce, *next;
 286         unsigned long expires;
 287
 288         mutex_lock(&rc->uwb_beca.mutex);
 289         list_for_each_entry_safe(bce, next, &rc->uwb_beca.list, node) {
 290                 expires = bce->ts_jiffies + msecs_to_jiffies(beacon_timeout_ms);
 291                 if (time_after(jiffies, expires)) {
 292                         uwbd_dev_offair(bce);
 293                 }
 294         }
 295         mutex_unlock(&rc->uwb_beca.mutex);
 296 }
 297
 298 /* Clean up the whole beacon cache. Called on shutdown */
 299 void uwb_beca_release(struct uwb_rc *rc)
 300 {
 301         struct uwb_beca_e *bce, *next;
 302
 303         mutex_lock(&rc->uwb_beca.mutex);
 304         list_for_each_entry_safe(bce, next, &rc->uwb_beca.list, node) {
 305                 list_del(&bce->node);
 306                 uwb_bce_put(bce);
 307         }
 308         mutex_unlock(&rc->uwb_beca.mutex);
 309 }
 310
 311 static void uwb_beacon_print(struct uwb_rc *rc, struct uwb_rc_evt_beacon *be,
 312                              struct uwb_beacon_frame *bf)
 313 {
 314         char macbuf[UWB_ADDR_STRSIZE];
 315         char devbuf[UWB_ADDR_STRSIZE];
 316         char dstbuf[UWB_ADDR_STRSIZE];
 317
 318         uwb_mac_addr_print(macbuf, sizeof(macbuf), &bf->Device_Identifier);
 319         uwb_dev_addr_print(devbuf, sizeof(devbuf), &bf->hdr.SrcAddr);
 320         uwb_dev_addr_print(dstbuf, sizeof(dstbuf), &bf->hdr.DestAddr);
 321         dev_info(&rc->uwb_dev.dev,
 322                  "BEACON from %s to %s (ch%u offset %u slot %u MAC %s)\n",
 323                  devbuf, dstbuf, be->bChannelNumber, be->wBPSTOffset,
 324                  bf->Beacon_Slot_Number, macbuf);
 325 }
 326
 327 /*
 328  * @bce: beacon cache entry, referenced
 329  */
 330 ssize_t uwb_bce_print_IEs(struct uwb_dev *uwb_dev, struct uwb_beca_e *bce,
 331                           char *buf, size_t size)
 332 {
 333         ssize_t result = 0;
 334         struct uwb_rc_evt_beacon *be;
 335         struct uwb_beacon_frame *bf;
 336         int ies_len;
 337         struct uwb_ie_hdr *ies;
 338
 339         mutex_lock(&bce->mutex);
 340
 341         be = bce->be;
 342         if (be) {
 343                 bf = (struct uwb_beacon_frame *)bce->be->BeaconInfo;
 344                 ies_len = be->wBeaconInfoLength - sizeof(struct uwb_beacon_frame);
 345                 ies = (struct uwb_ie_hdr *)bf->IEData;
 346
 347                 result = uwb_ie_dump_hex(ies, ies_len, buf, size);
 348         }
 349
 350         mutex_unlock(&bce->mutex);
 351
 352         return result;
 353 }
 354
 355 /*
 356  * Verify that the beacon event, frame and IEs are ok
 357  */
 358 static int uwb_verify_beacon(struct uwb_rc *rc, struct uwb_event *evt,
 359                              struct uwb_rc_evt_beacon *be)
 360 {
 361         int result = -EINVAL;
 362         struct uwb_beacon_frame *bf;
 363         struct device *dev = &rc->uwb_dev.dev;
 364
 365         /* Is there enough data to decode a beacon frame? */
 366         if (evt->notif.size < sizeof(*be) + sizeof(*bf)) {
 367                 dev_err(dev, "BEACON event: Not enough data to decode "
 368                         "(%zu vs %zu bytes needed)\n", evt->notif.size,
 369                         sizeof(*be) + sizeof(*bf));
 370                 goto error;
 371         }
 372         /* FIXME: make sure beacon frame IEs are fine and that the whole thing
 373          * is consistent */
 374         result = 0;
 375 error:
 376         return result;
 377 }
 378
 379 /*
 380  * Handle UWB_RC_EVT_BEACON events
 381  *
 382  * We check the beacon cache to see how the received beacon fares. If
 383  * is there already we refresh the timestamp. If not we create a new
 384  * entry.
 385  *
 386  * According to the WHCI and WUSB specs, only one beacon frame is
 387  * allowed per notification block, so we don't bother about scanning
 388  * for more.
 389  */
 390 int uwbd_evt_handle_rc_beacon(struct uwb_event *evt)
 391 {
 392         int result = -EINVAL;
 393         struct uwb_rc *rc;
 394         struct uwb_rc_evt_beacon *be;
 395         struct uwb_beacon_frame *bf;
 396         struct uwb_beca_e *bce;
 397         unsigned long last_ts;
 398
 399         rc = evt->rc;
 400         be = container_of(evt->notif.rceb, struct uwb_rc_evt_beacon, rceb);
 401         result = uwb_verify_beacon(rc, evt, be);
 402         if (result < 0)
 403                 return result;
 404
 405         /* FIXME: handle alien beacons. */
 406         if (be->bBeaconType == UWB_RC_BEACON_TYPE_OL_ALIEN ||
 407             be->bBeaconType == UWB_RC_BEACON_TYPE_NOL_ALIEN) {
 408                 return -ENOSYS;
 409         }
 410
 411         bf = (struct uwb_beacon_frame *) be->BeaconInfo;
 412
 413         /*
 414          * Drop beacons from devices with a NULL EUI-48 -- they cannot
 415          * be uniquely identified.
 416          *
 417          * It's expected that these will all be WUSB devices and they
 418          * have a WUSB specific connection method so ignoring them
 419          * here shouldn't be a problem.
 420          */
 421         if (uwb_mac_addr_bcast(&bf->Device_Identifier))
 422                 return 0;
 423
 424         mutex_lock(&rc->uwb_beca.mutex);
 425         bce = __uwb_beca_find_bymac(rc, &bf->Device_Identifier);
 426         if (bce == NULL) {
 427                 /* Not in there, a new device is pinging */
 428                 uwb_beacon_print(evt->rc, be, bf);
 429                 bce = __uwb_beca_add(rc, be, bf, evt->ts_jiffies);
 430                 if (bce == NULL) {
 431                         mutex_unlock(&rc->uwb_beca.mutex);
 432                         return -ENOMEM;
 433                 }
 434         }
 435         mutex_unlock(&rc->uwb_beca.mutex);
 436
 437         mutex_lock(&bce->mutex);
 438         /* purge old beacon data */
 439         kfree(bce->be);
 440
 441         last_ts = bce->ts_jiffies;
 442
 443         /* Update commonly used fields */
 444         bce->ts_jiffies = evt->ts_jiffies;
 445         bce->be = be;
 446         bce->dev_addr = bf->hdr.SrcAddr;
 447         bce->mac_addr = &bf->Device_Identifier;
 448         be->wBPSTOffset = le16_to_cpu(be->wBPSTOffset);
 449         be->wBeaconInfoLength = le16_to_cpu(be->wBeaconInfoLength);
 450         stats_add_sample(&bce->lqe_stats, be->bLQI - 7);
 451         stats_add_sample(&bce->rssi_stats, be->bRSSI + 18);
 452
 453         /*
 454          * This might be a beacon from a new device.
 455          */
 456         if (bce->uwb_dev == NULL)
 457                 uwbd_dev_onair(evt->rc, bce);
 458
 459         mutex_unlock(&bce->mutex);
 460
 461         return 1; /* we keep the event data */
 462 }
 463
 464 /*
 465  * Handle UWB_RC_EVT_BEACON_SIZE events
 466  *
 467  * XXXXX
 468  */
 469 int uwbd_evt_handle_rc_beacon_size(struct uwb_event *evt)
 470 {
 471         int result = -EINVAL;
 472         struct device *dev = &evt->rc->uwb_dev.dev;
 473         struct uwb_rc_evt_beacon_size *bs;
 474
 475         /* Is there enough data to decode the event? */
 476         if (evt->notif.size < sizeof(*bs)) {
 477                 dev_err(dev, "BEACON SIZE notification: Not enough data to "
 478                         "decode (%zu vs %zu bytes needed)\n",
 479                         evt->notif.size, sizeof(*bs));
 480                 goto error;
 481         }
 482         bs = container_of(evt->notif.rceb, struct uwb_rc_evt_beacon_size, rceb);
 483         if (0)
 484                 dev_info(dev, "Beacon size changed to %u bytes "
 485                         "(FIXME: action?)\n", le16_to_cpu(bs->wNewBeaconSize));
 486         else {
 487                 /* temporary hack until we do something with this message... */
 488                 static unsigned count;
 489                 if (++count % 1000 == 0)
 490                         dev_info(dev, "Beacon size changed %u times "
 491                                 "(FIXME: action?)\n", count);
 492         }
 493         result = 0;
 494 error:
 495         return result;
 496 }
 497
 498 /**
 499  * uwbd_evt_handle_rc_bp_slot_change - handle a BP_SLOT_CHANGE event
 500  * @evt: the BP_SLOT_CHANGE notification from the radio controller
 501  *
 502  * If the event indicates that no beacon period slots were available
 503  * then radio controller has transitioned to a non-beaconing state.
 504  * Otherwise, simply save the current beacon slot.
 505  */
 506 int uwbd_evt_handle_rc_bp_slot_change(struct uwb_event *evt)
 507 {
 508         struct uwb_rc *rc = evt->rc;
 509         struct device *dev = &rc->uwb_dev.dev;
 510         struct uwb_rc_evt_bp_slot_change *bpsc;
 511
 512         if (evt->notif.size < sizeof(*bpsc)) {
 513                 dev_err(dev, "BP SLOT CHANGE event: Not enough data\n");
 514                 return -EINVAL;
 515         }
 516         bpsc = container_of(evt->notif.rceb, struct uwb_rc_evt_bp_slot_change, rceb);
 517
 518         mutex_lock(&rc->uwb_dev.mutex);
 519         if (uwb_rc_evt_bp_slot_change_no_slot(bpsc)) {
 520                 dev_info(dev, "stopped beaconing: No free slots in BP\n");
 521                 rc->beaconing = -1;
 522         } else
 523                 rc->uwb_dev.beacon_slot = uwb_rc_evt_bp_slot_change_slot_num(bpsc);
 524         mutex_unlock(&rc->uwb_dev.mutex);
 525
 526         return 0;
 527 }
 528
 529 /**
 530  * Handle UWB_RC_EVT_BPOIE_CHANGE events
 531  *
 532  * XXXXX
 533  */
 534 struct uwb_ie_bpo {
 535         struct uwb_ie_hdr hdr;
 536         u8                bp_length;
 537         u8                data[];
 538 } __attribute__((packed));
 539
 540 int uwbd_evt_handle_rc_bpoie_change(struct uwb_event *evt)
 541 {
 542         int result = -EINVAL;
 543         struct device *dev = &evt->rc->uwb_dev.dev;
 544         struct uwb_rc_evt_bpoie_change *bpoiec;
 545         struct uwb_ie_bpo *bpoie;
 546         static unsigned count;  /* FIXME: this is a temp hack */
 547         size_t iesize;
 548
 549         /* Is there enough data to decode it? */
 550         if (evt->notif.size < sizeof(*bpoiec)) {
 551                 dev_err(dev, "BPOIEC notification: Not enough data to "
 552                         "decode (%zu vs %zu bytes needed)\n",
 553                         evt->notif.size, sizeof(*bpoiec));
 554                 goto error;
 555         }
 556         bpoiec = container_of(evt->notif.rceb, struct uwb_rc_evt_bpoie_change, rceb);
 557         iesize = le16_to_cpu(bpoiec->wBPOIELength);
 558         if (iesize < sizeof(*bpoie)) {
 559                 dev_err(dev, "BPOIEC notification: Not enough IE data to "
 560                         "decode (%zu vs %zu bytes needed)\n",
 561                         iesize, sizeof(*bpoie));
 562                 goto error;
 563         }
 564         if (++count % 1000 == 0)        /* Lame placeholder */
 565                 dev_info(dev, "BPOIE: %u changes received\n", count);
 566         /*
 567          * FIXME: At this point we should go over all the IEs in the
 568          *        bpoiec->BPOIE array and act on each.
 569          */
 570         result = 0;
 571 error:
 572         return result;
 573 }
 574
 575 /*
 576  * Print beaconing state.
 577  */
 578 static ssize_t uwb_rc_beacon_show(struct device *dev,
 579                                   struct device_attribute *attr, char *buf)
 580 {
 581         struct uwb_dev *uwb_dev = to_uwb_dev(dev);
 582         struct uwb_rc *rc = uwb_dev->rc;
 583         ssize_t result;
 584
 585         mutex_lock(&rc->uwb_dev.mutex);
 586         result = sprintf(buf, "%d\n", rc->beaconing);
 587         mutex_unlock(&rc->uwb_dev.mutex);
 588         return result;
 589 }
 590
 591 /*
 592  * Start beaconing on the specified channel, or stop beaconing.
 593  */
 594 static ssize_t uwb_rc_beacon_store(struct device *dev,
 595                                    struct device_attribute *attr,
 596                                    const char *buf, size_t size)
 597 {
 598         struct uwb_dev *uwb_dev = to_uwb_dev(dev);
 599         struct uwb_rc *rc = uwb_dev->rc;
 600         int channel;
 601         ssize_t result = -EINVAL;
 602
 603         result = sscanf(buf, "%d", &channel);
 604         if (result >= 1)
 605                 result = uwb_radio_force_channel(rc, channel);
 606
 607         return result < 0 ? result : size;
 608 }
 609 DEVICE_ATTR(beacon, S_IRUGO | S_IWUSR, uwb_rc_beacon_show, uwb_rc_beacon_store);