drivers/acpi/dock.c

   1 /*
   2  *  dock.c - ACPI dock station driver
   3  *
   4  *  Copyright (C) 2006 Kristen Carlson Accardi <kristen.c.accardi@intel.com>
   5  *
   6  * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   7  *
   8  *  This program is free software; you can redistribute it and/or modify
   9  *  it under the terms of the GNU General Public License as published by
  10  *  the Free Software Foundation; either version 2 of the License, or (at
  11  *  your option) any later version.
  12  *
  13  *  This program is distributed in the hope that it will be useful, but
  14  *  WITHOUT ANY WARRANTY; without even the implied warranty of
  15  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  16  *  General Public License for more details.
  17  *
  18  *  You should have received a copy of the GNU General Public License along
  19  *  with this program; if not, write to the Free Software Foundation, Inc.,
  20  *  59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
  21  *
  22  * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  23  */
  24
  25 #include <linux/kernel.h>
  26 #include <linux/module.h>
  27 #include <linux/init.h>
  28 #include <linux/types.h>
  29 #include <linux/notifier.h>
  30 #include <acpi/acpi_bus.h>
  31 #include <acpi/acpi_drivers.h>
  32
  33 #define ACPI_DOCK_DRIVER_NAME "ACPI Dock Station Driver"
  34
  35 ACPI_MODULE_NAME("dock")
  36 MODULE_AUTHOR("Kristen Carlson Accardi");
  37 MODULE_DESCRIPTION(ACPI_DOCK_DRIVER_NAME);
  38 MODULE_LICENSE("GPL");
  39
  40 static struct atomic_notifier_head dock_notifier_list;
  41
  42 struct dock_station {
  43         acpi_handle handle;
  44         unsigned long last_dock_time;
  45         u32 flags;
  46         spinlock_t dd_lock;
  47         spinlock_t hp_lock;
  48         struct list_head dependent_devices;
  49         struct list_head hotplug_devices;
  50 };
  51
  52 struct dock_dependent_device {
  53         struct list_head list;
  54         struct list_head hotplug_list;
  55         acpi_handle handle;
  56         acpi_notify_handler handler;
  57         void *context;
  58 };
  59
  60 #define DOCK_DOCKING    0x00000001
  61 #define DOCK_EVENT      KOBJ_DOCK
  62 #define UNDOCK_EVENT    KOBJ_UNDOCK
  63
  64 static struct dock_station *dock_station;
  65
  66 /*****************************************************************************
  67  *                         Dock Dependent device functions                   *
  68  *****************************************************************************/
  69 /**
  70  *  alloc_dock_dependent_device - allocate and init a dependent device
  71  *  @handle: the acpi_handle of the dependent device
  72  *
  73  *  Allocate memory for a dependent device structure for a device referenced
  74  *  by the acpi handle
  75  */
  76 static struct dock_dependent_device *
  77 alloc_dock_dependent_device(acpi_handle handle)
  78 {
  79         struct dock_dependent_device *dd;
  80
  81         dd = kzalloc(sizeof(*dd), GFP_KERNEL);
  82         if (dd) {
  83                 dd->handle = handle;
  84                 INIT_LIST_HEAD(&dd->list);
  85                 INIT_LIST_HEAD(&dd->hotplug_list);
  86         }
  87         return dd;
  88 }
  89
  90 /**
  91  * add_dock_dependent_device - associate a device with the dock station
  92  * @ds: The dock station
  93  * @dd: The dependent device
  94  *
  95  * Add the dependent device to the dock's dependent device list.
  96  */
  97 static void
  98 add_dock_dependent_device(struct dock_station *ds,
  99                           struct dock_dependent_device *dd)
 100 {
 101         spin_lock(&ds->dd_lock);
 102         list_add_tail(&dd->list, &ds->dependent_devices);
 103         spin_unlock(&ds->dd_lock);
 104 }
 105
 106 /**
 107  * dock_add_hotplug_device - associate a hotplug handler with the dock station
 108  * @ds: The dock station
 109  * @dd: The dependent device struct
 110  *
 111  * Add the dependent device to the dock's hotplug device list
 112  */
 113 static void
 114 dock_add_hotplug_device(struct dock_station *ds,
 115                         struct dock_dependent_device *dd)
 116 {
 117         spin_lock(&ds->hp_lock);
 118         list_add_tail(&dd->hotplug_list, &ds->hotplug_devices);
 119         spin_unlock(&ds->hp_lock);
 120 }
 121
 122 /**
 123  * dock_del_hotplug_device - remove a hotplug handler from the dock station
 124  * @ds: The dock station
 125  * @dd: the dependent device struct
 126  *
 127  * Delete the dependent device from the dock's hotplug device list
 128  */
 129 static void
 130 dock_del_hotplug_device(struct dock_station *ds,
 131                         struct dock_dependent_device *dd)
 132 {
 133         spin_lock(&ds->hp_lock);
 134         list_del(&dd->hotplug_list);
 135         spin_unlock(&ds->hp_lock);
 136 }
 137
 138 /**
 139  * find_dock_dependent_device - get a device dependent on this dock
 140  * @ds: the dock station
 141  * @handle: the acpi_handle of the device we want
 142  *
 143  * iterate over the dependent device list for this dock.  If the
 144  * dependent device matches the handle, return.
 145  */
 146 static struct dock_dependent_device *
 147 find_dock_dependent_device(struct dock_station *ds, acpi_handle handle)
 148 {
 149         struct dock_dependent_device *dd;
 150
 151         spin_lock(&ds->dd_lock);
 152         list_for_each_entry(dd, &ds->dependent_devices, list) {
 153                 if (handle == dd->handle) {
 154                         spin_unlock(&ds->dd_lock);
 155                         return dd;
 156                 }
 157         }
 158         spin_unlock(&ds->dd_lock);
 159         return NULL;
 160 }
 161
 162 /*****************************************************************************
 163  *                         Dock functions                                    *
 164  *****************************************************************************/
 165 /**
 166  * is_dock - see if a device is a dock station
 167  * @handle: acpi handle of the device
 168  *
 169  * If an acpi object has a _DCK method, then it is by definition a dock
 170  * station, so return true.
 171  */
 172 static int is_dock(acpi_handle handle)
 173 {
 174         acpi_status status;
 175         acpi_handle tmp;
 176
 177         status = acpi_get_handle(handle, "_DCK", &tmp);
 178         if (ACPI_FAILURE(status))
 179                 return 0;
 180         return 1;
 181 }
 182
 183 /**
 184  * is_dock_device - see if a device is on a dock station
 185  * @handle: acpi handle of the device
 186  *
 187  * If this device is either the dock station itself,
 188  * or is a device dependent on the dock station, then it
 189  * is a dock device
 190  */
 191 int is_dock_device(acpi_handle handle)
 192 {
 193         if (!dock_station)
 194                 return 0;
 195
 196         if (is_dock(handle) || find_dock_dependent_device(dock_station, handle))
 197                 return 1;
 198
 199         return 0;
 200 }
 201
 202 EXPORT_SYMBOL_GPL(is_dock_device);
 203
 204 /**
 205  * dock_present - see if the dock station is present.
 206  * @ds: the dock station
 207  *
 208  * execute the _STA method.  note that present does not
 209  * imply that we are docked.
 210  */
 211 static int dock_present(struct dock_station *ds)
 212 {
 213         unsigned long sta;
 214         acpi_status status;
 215
 216         if (ds) {
 217                 status = acpi_evaluate_integer(ds->handle, "_STA", NULL, &sta);
 218                 if (ACPI_SUCCESS(status) && sta)
 219                         return 1;
 220         }
 221         return 0;
 222 }
 223
 224
 225
 226 /**
 227  * dock_create_acpi_device - add new devices to acpi
 228  * @handle - handle of the device to add
 229  *
 230  *  This function will create a new acpi_device for the given
 231  *  handle if one does not exist already.  This should cause
 232  *  acpi to scan for drivers for the given devices, and call
 233  *  matching driver's add routine.
 234  *
 235  *  Returns a pointer to the acpi_device corresponding to the handle.
 236  */
 237 static struct acpi_device * dock_create_acpi_device(acpi_handle handle)
 238 {
 239         struct acpi_device *device = NULL;
 240         struct acpi_device *parent_device;
 241         acpi_handle parent;
 242         int ret;
 243
 244         if (acpi_bus_get_device(handle, &device)) {
 245                 /*
 246                  * no device created for this object,
 247                  * so we should create one.
 248                  */
 249                 acpi_get_parent(handle, &parent);
 250                 if (acpi_bus_get_device(parent, &parent_device))
 251                         parent_device = NULL;
 252
 253                 ret = acpi_bus_add(&device, parent_device, handle,
 254                         ACPI_BUS_TYPE_DEVICE);
 255                 if (ret) {
 256                         pr_debug("error adding bus, %x\n",
 257                                 -ret);
 258                         return NULL;
 259                 }
 260         }
 261         return device;
 262 }
 263
 264 /**
 265  * dock_remove_acpi_device - remove the acpi_device struct from acpi
 266  * @handle - the handle of the device to remove
 267  *
 268  *  Tell acpi to remove the acpi_device.  This should cause any loaded
 269  *  driver to have it's remove routine called.
 270  */
 271 static void dock_remove_acpi_device(acpi_handle handle)
 272 {
 273         struct acpi_device *device;
 274         int ret;
 275
 276         if (!acpi_bus_get_device(handle, &device)) {
 277                 ret = acpi_bus_trim(device, 1);
 278                 if (ret)
 279                         pr_debug("error removing bus, %x\n", -ret);
 280         }
 281 }
 282
 283
 284 /**
 285  * hotplug_dock_devices - insert or remove devices on the dock station
 286  * @ds: the dock station
 287  * @event: either bus check or eject request
 288  *
 289  * Some devices on the dock station need to have drivers called
 290  * to perform hotplug operations after a dock event has occurred.
 291  * Traverse the list of dock devices that have registered a
 292  * hotplug handler, and call the handler.
 293  */
 294 static void hotplug_dock_devices(struct dock_station *ds, u32 event)
 295 {
 296         struct dock_dependent_device *dd;
 297
 298         spin_lock(&ds->hp_lock);
 299
 300         /*
 301          * First call driver specific hotplug functions
 302          */
 303         list_for_each_entry(dd, &ds->hotplug_devices, hotplug_list) {
 304                 if (dd->handler)
 305                         dd->handler(dd->handle, event, dd->context);
 306         }
 307
 308         /*
 309          * Now make sure that an acpi_device is created for each
 310          * dependent device, or removed if this is an eject request.
 311          * This will cause acpi_drivers to be stopped/started if they
 312          * exist
 313          */
 314         list_for_each_entry(dd, &ds->dependent_devices, list) {
 315                 if (event == ACPI_NOTIFY_EJECT_REQUEST)
 316                         dock_remove_acpi_device(dd->handle);
 317                 else
 318                         dock_create_acpi_device(dd->handle);
 319         }
 320         spin_unlock(&ds->hp_lock);
 321 }
 322
 323 static void dock_event(struct dock_station *ds, u32 event, int num)
 324 {
 325         struct acpi_device *device;
 326
 327         device = dock_create_acpi_device(ds->handle);
 328         if (device)
 329                 kobject_uevent(&device->kobj, num);
 330 }
 331
 332 /**
 333  * eject_dock - respond to a dock eject request
 334  * @ds: the dock station
 335  *
 336  * This is called after _DCK is called, to execute the dock station's
 337  * _EJ0 method.
 338  */
 339 static void eject_dock(struct dock_station *ds)
 340 {
 341         struct acpi_object_list arg_list;
 342         union acpi_object arg;
 343         acpi_status status;
 344         acpi_handle tmp;
 345
 346         /* all dock devices should have _EJ0, but check anyway */
 347         status = acpi_get_handle(ds->handle, "_EJ0", &tmp);
 348         if (ACPI_FAILURE(status)) {
 349                 pr_debug("No _EJ0 support for dock device\n");
 350                 return;
 351         }
 352
 353         arg_list.count = 1;
 354         arg_list.pointer = &arg;
 355         arg.type = ACPI_TYPE_INTEGER;
 356         arg.integer.value = 1;
 357
 358         if (ACPI_FAILURE(acpi_evaluate_object(ds->handle, "_EJ0",
 359                                               &arg_list, NULL)))
 360                 pr_debug("Failed to evaluate _EJ0!\n");
 361 }
 362
 363 /**
 364  * handle_dock - handle a dock event
 365  * @ds: the dock station
 366  * @dock: to dock, or undock - that is the question
 367  *
 368  * Execute the _DCK method in response to an acpi event
 369  */
 370 static void handle_dock(struct dock_station *ds, int dock)
 371 {
 372         acpi_status status;
 373         struct acpi_object_list arg_list;
 374         union acpi_object arg;
 375         struct acpi_buffer buffer = { ACPI_ALLOCATE_BUFFER, NULL };
 376         struct acpi_buffer name_buffer = { ACPI_ALLOCATE_BUFFER, NULL };
 377         union acpi_object *obj;
 378
 379         acpi_get_name(ds->handle, ACPI_FULL_PATHNAME, &name_buffer);
 380         obj = name_buffer.pointer;
 381
 382         printk(KERN_INFO PREFIX "%s\n", dock ? "docking" : "undocking");
 383
 384         /* _DCK method has one argument */
 385         arg_list.count = 1;
 386         arg_list.pointer = &arg;
 387         arg.type = ACPI_TYPE_INTEGER;
 388         arg.integer.value = dock;
 389         status = acpi_evaluate_object(ds->handle, "_DCK", &arg_list, &buffer);
 390         if (ACPI_FAILURE(status))
 391                 pr_debug("%s: failed to execute _DCK\n", obj->string.pointer);
 392         kfree(buffer.pointer);
 393         kfree(name_buffer.pointer);
 394 }
 395
 396 static inline void dock(struct dock_station *ds)
 397 {
 398         handle_dock(ds, 1);
 399 }
 400
 401 static inline void undock(struct dock_station *ds)
 402 {
 403         handle_dock(ds, 0);
 404 }
 405
 406 static inline void begin_dock(struct dock_station *ds)
 407 {
 408         ds->flags |= DOCK_DOCKING;
 409 }
 410
 411 static inline void complete_dock(struct dock_station *ds)
 412 {
 413         ds->flags &= ~(DOCK_DOCKING);
 414         ds->last_dock_time = jiffies;
 415 }
 416
 417 /**
 418  * dock_in_progress - see if we are in the middle of handling a dock event
 419  * @ds: the dock station
 420  *
 421  * Sometimes while docking, false dock events can be sent to the driver
 422  * because good connections aren't made or some other reason.  Ignore these
 423  * if we are in the middle of doing something.
 424  */
 425 static int dock_in_progress(struct dock_station *ds)
 426 {
 427         if ((ds->flags & DOCK_DOCKING) ||
 428             time_before(jiffies, (ds->last_dock_time + HZ)))
 429                 return 1;
 430         return 0;
 431 }
 432
 433 /**
 434  * register_dock_notifier - add yourself to the dock notifier list
 435  * @nb: the callers notifier block
 436  *
 437  * If a driver wishes to be notified about dock events, they can
 438  * use this function to put a notifier block on the dock notifier list.
 439  * this notifier call chain will be called after a dock event, but
 440  * before hotplugging any new devices.
 441  */
 442 int register_dock_notifier(struct notifier_block *nb)
 443 {
 444         return atomic_notifier_chain_register(&dock_notifier_list, nb);
 445 }
 446
 447 EXPORT_SYMBOL_GPL(register_dock_notifier);
 448
 449 /**
 450  * unregister_dock_notifier - remove yourself from the dock notifier list
 451  * @nb: the callers notifier block
 452  */
 453 void unregister_dock_notifier(struct notifier_block *nb)
 454 {
 455         atomic_notifier_chain_unregister(&dock_notifier_list, nb);
 456 }
 457
 458 EXPORT_SYMBOL_GPL(unregister_dock_notifier);
 459
 460 /**
 461  * register_hotplug_dock_device - register a hotplug function
 462  * @handle: the handle of the device
 463  * @handler: the acpi_notifier_handler to call after docking
 464  * @context: device specific data
 465  *
 466  * If a driver would like to perform a hotplug operation after a dock
 467  * event, they can register an acpi_notifiy_handler to be called by
 468  * the dock driver after _DCK is executed.
 469  */
 470 int
 471 register_hotplug_dock_device(acpi_handle handle, acpi_notify_handler handler,
 472                              void *context)
 473 {
 474         struct dock_dependent_device *dd;
 475
 476         if (!dock_station)
 477                 return -ENODEV;
 478
 479         /*
 480          * make sure this handle is for a device dependent on the dock,
 481          * this would include the dock station itself
 482          */
 483         dd = find_dock_dependent_device(dock_station, handle);
 484         if (dd) {
 485                 dd->handler = handler;
 486                 dd->context = context;
 487                 dock_add_hotplug_device(dock_station, dd);
 488                 return 0;
 489         }
 490
 491         return -EINVAL;
 492 }
 493
 494 EXPORT_SYMBOL_GPL(register_hotplug_dock_device);
 495
 496 /**
 497  * unregister_hotplug_dock_device - remove yourself from the hotplug list
 498  * @handle: the acpi handle of the device
 499  */
 500 void unregister_hotplug_dock_device(acpi_handle handle)
 501 {
 502         struct dock_dependent_device *dd;
 503
 504         if (!dock_station)
 505                 return;
 506
 507         dd = find_dock_dependent_device(dock_station, handle);
 508         if (dd)
 509                 dock_del_hotplug_device(dock_station, dd);
 510 }
 511
 512 EXPORT_SYMBOL_GPL(unregister_hotplug_dock_device);
 513
 514 /**
 515  * dock_notify - act upon an acpi dock notification
 516  * @handle: the dock station handle
 517  * @event: the acpi event
 518  * @data: our driver data struct
 519  *
 520  * If we are notified to dock, then check to see if the dock is
 521  * present and then dock.  Notify all drivers of the dock event,
 522  * and then hotplug and devices that may need hotplugging.  For undock
 523  * check to make sure the dock device is still present, then undock
 524  * and hotremove all the devices that may need removing.
 525  */
 526 static void dock_notify(acpi_handle handle, u32 event, void *data)
 527 {
 528         struct dock_station *ds = (struct dock_station *)data;
 529
 530         switch (event) {
 531         case ACPI_NOTIFY_BUS_CHECK:
 532                 if (!dock_in_progress(ds) && dock_present(ds)) {
 533                         begin_dock(ds);
 534                         dock(ds);
 535                         if (!dock_present(ds)) {
 536                                 printk(KERN_ERR PREFIX "Unable to dock!\n");
 537                                 break;
 538                         }
 539                         atomic_notifier_call_chain(&dock_notifier_list,
 540                                                    event, NULL);
 541                         hotplug_dock_devices(ds, event);
 542                         complete_dock(ds);
 543                         dock_event(ds, event, DOCK_EVENT);
 544                 }
 545                 break;
 546         case ACPI_NOTIFY_DEVICE_CHECK:
 547         /*
 548          * According to acpi spec 3.0a, if a DEVICE_CHECK notification
 549          * is sent and _DCK is present, it is assumed to mean an
 550          * undock request.  This notify routine will only be called
 551          * for objects defining _DCK, so we will fall through to eject
 552          * request here.  However, we will pass an eject request through
 553          * to the driver who wish to hotplug.
 554          */
 555         case ACPI_NOTIFY_EJECT_REQUEST:
 556                 if (!dock_in_progress(ds) && dock_present(ds)) {
 557                         /*
 558                          * here we need to generate the undock
 559                          * event prior to actually doing the undock
 560                          * so that the device struct still exists.
 561                          */
 562                         dock_event(ds, event, UNDOCK_EVENT);
 563                         hotplug_dock_devices(ds, ACPI_NOTIFY_EJECT_REQUEST);
 564                         undock(ds);
 565                         eject_dock(ds);
 566                         if (dock_present(ds))
 567                                 printk(KERN_ERR PREFIX "Unable to undock!\n");
 568                 }
 569                 break;
 570         default:
 571                 printk(KERN_ERR PREFIX "Unknown dock event %d\n", event);
 572         }
 573 }
 574
 575 /**
 576  * find_dock_devices - find devices on the dock station
 577  * @handle: the handle of the device we are examining
 578  * @lvl: unused
 579  * @context: the dock station private data
 580  * @rv: unused
 581  *
 582  * This function is called by acpi_walk_namespace.  It will
 583  * check to see if an object has an _EJD method.  If it does, then it
 584  * will see if it is dependent on the dock station.
 585  */
 586 static acpi_status
 587 find_dock_devices(acpi_handle handle, u32 lvl, void *context, void **rv)
 588 {
 589         acpi_status status;
 590         acpi_handle tmp;
 591         struct dock_station *ds = (struct dock_station *)context;
 592         struct dock_dependent_device *dd;
 593
 594         status = acpi_bus_get_ejd(handle, &tmp);
 595         if (ACPI_FAILURE(status))
 596                 return AE_OK;
 597
 598         if (tmp == ds->handle) {
 599                 dd = alloc_dock_dependent_device(handle);
 600                 if (dd)
 601                         add_dock_dependent_device(ds, dd);
 602         }
 603
 604         return AE_OK;
 605 }
 606
 607 /**
 608  * dock_add - add a new dock station
 609  * @handle: the dock station handle
 610  *
 611  * allocated and initialize a new dock station device.  Find all devices
 612  * that are on the dock station, and register for dock event notifications.
 613  */
 614 static int dock_add(acpi_handle handle)
 615 {
 616         int ret;
 617         acpi_status status;
 618         struct dock_dependent_device *dd;
 619
 620         /* allocate & initialize the dock_station private data */
 621         dock_station = kzalloc(sizeof(*dock_station), GFP_KERNEL);
 622         if (!dock_station)
 623                 return -ENOMEM;
 624         dock_station->handle = handle;
 625         dock_station->last_dock_time = jiffies - HZ;
 626         INIT_LIST_HEAD(&dock_station->dependent_devices);
 627         INIT_LIST_HEAD(&dock_station->hotplug_devices);
 628         spin_lock_init(&dock_station->dd_lock);
 629         spin_lock_init(&dock_station->hp_lock);
 630         ATOMIC_INIT_NOTIFIER_HEAD(&dock_notifier_list);
 631
 632         /* Find dependent devices */
 633         acpi_walk_namespace(ACPI_TYPE_DEVICE, ACPI_ROOT_OBJECT,
 634                             ACPI_UINT32_MAX, find_dock_devices, dock_station,
 635                             NULL);
 636
 637         /* add the dock station as a device dependent on itself */
 638         dd = alloc_dock_dependent_device(handle);
 639         if (!dd) {
 640                 kfree(dock_station);
 641                 return -ENOMEM;
 642         }
 643         add_dock_dependent_device(dock_station, dd);
 644
 645         /* register for dock events */
 646         status = acpi_install_notify_handler(dock_station->handle,
 647                                              ACPI_SYSTEM_NOTIFY,
 648                                              dock_notify, dock_station);
 649
 650         if (ACPI_FAILURE(status)) {
 651                 printk(KERN_ERR PREFIX "Error installing notify handler\n");
 652                 ret = -ENODEV;
 653                 goto dock_add_err;
 654         }
 655
 656         printk(KERN_INFO PREFIX "%s \n", ACPI_DOCK_DRIVER_NAME);
 657
 658         return 0;
 659
 660 dock_add_err:
 661         kfree(dock_station);
 662         kfree(dd);
 663         return ret;
 664 }
 665
 666 /**
 667  * dock_remove - free up resources related to the dock station
 668  */
 669 static int dock_remove(void)
 670 {
 671         struct dock_dependent_device *dd, *tmp;
 672         acpi_status status;
 673
 674         if (!dock_station)
 675                 return 0;
 676
 677         /* remove dependent devices */
 678         list_for_each_entry_safe(dd, tmp, &dock_station->dependent_devices,
 679                                  list)
 680             kfree(dd);
 681
 682         /* remove dock notify handler */
 683         status = acpi_remove_notify_handler(dock_station->handle,
 684                                             ACPI_SYSTEM_NOTIFY,
 685                                             dock_notify);
 686         if (ACPI_FAILURE(status))
 687                 printk(KERN_ERR "Error removing notify handler\n");
 688
 689         /* free dock station memory */
 690         kfree(dock_station);
 691         return 0;
 692 }
 693
 694 /**
 695  * find_dock - look for a dock station
 696  * @handle: acpi handle of a device
 697  * @lvl: unused
 698  * @context: counter of dock stations found
 699  * @rv: unused
 700  *
 701  * This is called by acpi_walk_namespace to look for dock stations.
 702  */
 703 static acpi_status
 704 find_dock(acpi_handle handle, u32 lvl, void *context, void **rv)
 705 {
 706         int *count = (int *)context;
 707         acpi_status status = AE_OK;
 708
 709         if (is_dock(handle)) {
 710                 if (dock_add(handle) >= 0) {
 711                         (*count)++;
 712                         status = AE_CTRL_TERMINATE;
 713                 }
 714         }
 715         return status;
 716 }
 717
 718 static int __init dock_init(void)
 719 {
 720         int num = 0;
 721
 722         dock_station = NULL;
 723
 724         /* look for a dock station */
 725         acpi_walk_namespace(ACPI_TYPE_DEVICE, ACPI_ROOT_OBJECT,
 726                             ACPI_UINT32_MAX, find_dock, &num, NULL);
 727
 728         if (!num)
 729                 return -ENODEV;
 730
 731         return 0;
 732 }
 733
 734 static void __exit dock_exit(void)
 735 {
 736         dock_remove();
 737 }
 738
 739 postcore_initcall(dock_init);
 740 module_exit(dock_exit);