drivers/acpi/power.c

   1 /*
   2  *  acpi_power.c - ACPI Bus Power Management ($Revision: 39 $)
   3  *
   4  *  Copyright (C) 2001, 2002 Andy Grover <andrew.grover@intel.com>
   5  *  Copyright (C) 2001, 2002 Paul Diefenbaugh <paul.s.diefenbaugh@intel.com>
   6  *
   7  * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   8  *
   9  *  This program is free software; you can redistribute it and/or modify
  10  *  it under the terms of the GNU General Public License as published by
  11  *  the Free Software Foundation; either version 2 of the License, or (at
  12  *  your option) any later version.
  13  *
  14  *  This program is distributed in the hope that it will be useful, but
  15  *  WITHOUT ANY WARRANTY; without even the implied warranty of
  16  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  17  *  General Public License for more details.
  18  *
  19  *  You should have received a copy of the GNU General Public License along
  20  *  with this program; if not, write to the Free Software Foundation, Inc.,
  21  *  59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
  22  *
  23  * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  24  */
  25
  26 /*
  27  * ACPI power-managed devices may be controlled in two ways:
  28  * 1. via "Device Specific (D-State) Control"
  29  * 2. via "Power Resource Control".
  30  * This module is used to manage devices relying on Power Resource Control.
  31  *
  32  * An ACPI "power resource object" describes a software controllable power
  33  * plane, clock plane, or other resource used by a power managed device.
  34  * A device may rely on multiple power resources, and a power resource
  35  * may be shared by multiple devices.
  36  */
  37
  38 #include <linux/kernel.h>
  39 #include <linux/module.h>
  40 #include <linux/init.h>
  41 #include <linux/types.h>
  42 #include <linux/proc_fs.h>
  43 #include <linux/seq_file.h>
  44 #include <acpi/acpi_bus.h>
  45 #include <acpi/acpi_drivers.h>
  46
  47 #define _COMPONENT              ACPI_POWER_COMPONENT
  48 ACPI_MODULE_NAME("power");
  49 #define ACPI_POWER_COMPONENT            0x00800000
  50 #define ACPI_POWER_CLASS                "power_resource"
  51 #define ACPI_POWER_DEVICE_NAME          "Power Resource"
  52 #define ACPI_POWER_FILE_INFO            "info"
  53 #define ACPI_POWER_FILE_STATUS          "state"
  54 #define ACPI_POWER_RESOURCE_STATE_OFF   0x00
  55 #define ACPI_POWER_RESOURCE_STATE_ON    0x01
  56 #define ACPI_POWER_RESOURCE_STATE_UNKNOWN 0xFF
  57 static int acpi_power_add(struct acpi_device *device);
  58 static int acpi_power_remove(struct acpi_device *device, int type);
  59 static int acpi_power_resume(struct acpi_device *device);
  60 static int acpi_power_open_fs(struct inode *inode, struct file *file);
  61
  62 static struct acpi_driver acpi_power_driver = {
  63         .name = "power",
  64         .class = ACPI_POWER_CLASS,
  65         .ids = ACPI_POWER_HID,
  66         .ops = {
  67                 .add = acpi_power_add,
  68                 .remove = acpi_power_remove,
  69                 .resume = acpi_power_resume,
  70                 },
  71 };
  72
  73 struct acpi_power_reference {
  74         struct list_head node;
  75         struct acpi_device *device;
  76 };
  77
  78 struct acpi_power_resource {
  79         struct acpi_device * device;
  80         acpi_bus_id name;
  81         u32 system_level;
  82         u32 order;
  83         int state;
  84         struct mutex resource_lock;
  85         struct list_head reference;
  86 };
  87
  88 static struct list_head acpi_power_resource_list;
  89
  90 static const struct file_operations acpi_power_fops = {
  91         .open = acpi_power_open_fs,
  92         .read = seq_read,
  93         .llseek = seq_lseek,
  94         .release = single_release,
  95 };
  96
  97 /* --------------------------------------------------------------------------
  98                              Power Resource Management
  99    -------------------------------------------------------------------------- */
 100
 101 static int
 102 acpi_power_get_context(acpi_handle handle,
 103                        struct acpi_power_resource **resource)
 104 {
 105         int result = 0;
 106         struct acpi_device *device = NULL;
 107
 108
 109         if (!resource)
 110                 return -ENODEV;
 111
 112         result = acpi_bus_get_device(handle, &device);
 113         if (result) {
 114                 printk(KERN_WARNING PREFIX "Getting context [%p]\n", handle);
 115                 return result;
 116         }
 117
 118         *resource = acpi_driver_data(device);
 119         if (!resource)
 120                 return -ENODEV;
 121
 122         return 0;
 123 }
 124
 125 static int acpi_power_get_state(struct acpi_power_resource *resource)
 126 {
 127         acpi_status status = AE_OK;
 128         unsigned long sta = 0;
 129
 130
 131         if (!resource)
 132                 return -EINVAL;
 133
 134         status = acpi_evaluate_integer(resource->device->handle, "_STA", NULL, &sta);
 135         if (ACPI_FAILURE(status))
 136                 return -ENODEV;
 137
 138         if (sta & 0x01)
 139                 resource->state = ACPI_POWER_RESOURCE_STATE_ON;
 140         else
 141                 resource->state = ACPI_POWER_RESOURCE_STATE_OFF;
 142
 143         ACPI_DEBUG_PRINT((ACPI_DB_INFO, "Resource [%s] is %s\n",
 144                           resource->name, resource->state ? "on" : "off"));
 145
 146         return 0;
 147 }
 148
 149 static int acpi_power_get_list_state(struct acpi_handle_list *list, int *state)
 150 {
 151         int result = 0;
 152         struct acpi_power_resource *resource = NULL;
 153         u32 i = 0;
 154
 155
 156         if (!list || !state)
 157                 return -EINVAL;
 158
 159         /* The state of the list is 'on' IFF all resources are 'on'. */
 160
 161         for (i = 0; i < list->count; i++) {
 162                 result = acpi_power_get_context(list->handles[i], &resource);
 163                 if (result)
 164                         return result;
 165                 result = acpi_power_get_state(resource);
 166                 if (result)
 167                         return result;
 168
 169                 *state = resource->state;
 170
 171                 if (*state != ACPI_POWER_RESOURCE_STATE_ON)
 172                         break;
 173         }
 174
 175         ACPI_DEBUG_PRINT((ACPI_DB_INFO, "Resource list is %s\n",
 176                           *state ? "on" : "off"));
 177
 178         return result;
 179 }
 180
 181 static int acpi_power_on(acpi_handle handle, struct acpi_device *dev)
 182 {
 183         int result = 0;
 184         int found = 0;
 185         acpi_status status = AE_OK;
 186         struct acpi_power_resource *resource = NULL;
 187         struct list_head *node, *next;
 188         struct acpi_power_reference *ref;
 189
 190
 191         result = acpi_power_get_context(handle, &resource);
 192         if (result)
 193                 return result;
 194
 195         mutex_lock(&resource->resource_lock);
 196         list_for_each_safe(node, next, &resource->reference) {
 197                 ref = container_of(node, struct acpi_power_reference, node);
 198                 if (dev->handle == ref->device->handle) {
 199                         ACPI_DEBUG_PRINT((ACPI_DB_INFO, "Device [%s] already referenced by resource [%s]\n",
 200                                   dev->pnp.bus_id, resource->name));
 201                         found = 1;
 202                         break;
 203                 }
 204         }
 205
 206         if (!found) {
 207                 ref = kmalloc(sizeof (struct acpi_power_reference),
 208                     irqs_disabled() ? GFP_ATOMIC : GFP_KERNEL);
 209                 if (!ref) {
 210                         ACPI_DEBUG_PRINT((ACPI_DB_INFO, "kmalloc() failed\n"));
 211                         mutex_unlock(&resource->resource_lock);
 212                         return -ENOMEM;
 213                 }
 214                 list_add_tail(&ref->node, &resource->reference);
 215                 ref->device = dev;
 216                 ACPI_DEBUG_PRINT((ACPI_DB_INFO, "Device [%s] added to resource [%s] references\n",
 217                           dev->pnp.bus_id, resource->name));
 218         }
 219         mutex_unlock(&resource->resource_lock);
 220
 221         if (resource->state == ACPI_POWER_RESOURCE_STATE_ON) {
 222                 ACPI_DEBUG_PRINT((ACPI_DB_INFO, "Resource [%s] already on\n",
 223                                   resource->name));
 224                 return 0;
 225         }
 226
 227         status = acpi_evaluate_object(resource->device->handle, "_ON", NULL, NULL);
 228         if (ACPI_FAILURE(status))
 229                 return -ENODEV;
 230
 231         result = acpi_power_get_state(resource);
 232         if (result)
 233                 return result;
 234         if (resource->state != ACPI_POWER_RESOURCE_STATE_ON)
 235                 return -ENOEXEC;
 236
 237         /* Update the power resource's _device_ power state */
 238         resource->device->power.state = ACPI_STATE_D0;
 239
 240         ACPI_DEBUG_PRINT((ACPI_DB_INFO, "Resource [%s] turned on\n",
 241                           resource->name));
 242         return 0;
 243 }
 244
 245 static int acpi_power_off_device(acpi_handle handle, struct acpi_device *dev)
 246 {
 247         int result = 0;
 248         acpi_status status = AE_OK;
 249         struct acpi_power_resource *resource = NULL;
 250         struct list_head *node, *next;
 251         struct acpi_power_reference *ref;
 252
 253
 254         result = acpi_power_get_context(handle, &resource);
 255         if (result)
 256                 return result;
 257
 258         mutex_lock(&resource->resource_lock);
 259         list_for_each_safe(node, next, &resource->reference) {
 260                 ref = container_of(node, struct acpi_power_reference, node);
 261                 if (dev->handle == ref->device->handle) {
 262                         list_del(&ref->node);
 263                         kfree(ref);
 264                         ACPI_DEBUG_PRINT((ACPI_DB_INFO, "Device [%s] removed from resource [%s] references\n",
 265                             dev->pnp.bus_id, resource->name));
 266                         break;
 267                 }
 268         }
 269
 270         if (!list_empty(&resource->reference)) {
 271                 ACPI_DEBUG_PRINT((ACPI_DB_INFO, "Cannot turn resource [%s] off - resource is in use\n",
 272                     resource->name));
 273                 mutex_unlock(&resource->resource_lock);
 274                 return 0;
 275         }
 276         mutex_unlock(&resource->resource_lock);
 277
 278         if (resource->state == ACPI_POWER_RESOURCE_STATE_OFF) {
 279                 ACPI_DEBUG_PRINT((ACPI_DB_INFO, "Resource [%s] already off\n",
 280                                   resource->name));
 281                 return 0;
 282         }
 283
 284         status = acpi_evaluate_object(resource->device->handle, "_OFF", NULL, NULL);
 285         if (ACPI_FAILURE(status))
 286                 return -ENODEV;
 287
 288         result = acpi_power_get_state(resource);
 289         if (result)
 290                 return result;
 291         if (resource->state != ACPI_POWER_RESOURCE_STATE_OFF)
 292                 return -ENOEXEC;
 293
 294         /* Update the power resource's _device_ power state */
 295         resource->device->power.state = ACPI_STATE_D3;
 296
 297         ACPI_DEBUG_PRINT((ACPI_DB_INFO, "Resource [%s] turned off\n",
 298                           resource->name));
 299
 300         return 0;
 301 }
 302
 303 /*
 304  * Prepare a wakeup device, two steps (Ref ACPI 2.0:P229):
 305  * 1. Power on the power resources required for the wakeup device
 306  * 2. Enable _PSW (power state wake) for the device if present
 307  */
 308 int acpi_enable_wakeup_device_power(struct acpi_device *dev)
 309 {
 310         union acpi_object arg = { ACPI_TYPE_INTEGER };
 311         struct acpi_object_list arg_list = { 1, &arg };
 312         acpi_status status = AE_OK;
 313         int i;
 314         int ret = 0;
 315
 316         if (!dev || !dev->wakeup.flags.valid)
 317                 return -1;
 318
 319         arg.integer.value = 1;
 320         /* Open power resource */
 321         for (i = 0; i < dev->wakeup.resources.count; i++) {
 322                 ret = acpi_power_on(dev->wakeup.resources.handles[i], dev);
 323                 if (ret) {
 324                         printk(KERN_ERR PREFIX "Transition power state\n");
 325                         dev->wakeup.flags.valid = 0;
 326                         return -1;
 327                 }
 328         }
 329
 330         /* Execute PSW */
 331         status = acpi_evaluate_object(dev->handle, "_PSW", &arg_list, NULL);
 332         if (ACPI_FAILURE(status) && (status != AE_NOT_FOUND)) {
 333                 printk(KERN_ERR PREFIX "Evaluate _PSW\n");
 334                 dev->wakeup.flags.valid = 0;
 335                 ret = -1;
 336         }
 337
 338         return ret;
 339 }
 340
 341 /*
 342  * Shutdown a wakeup device, counterpart of above method
 343  * 1. Disable _PSW (power state wake)
 344  * 2. Shutdown down the power resources
 345  */
 346 int acpi_disable_wakeup_device_power(struct acpi_device *dev)
 347 {
 348         union acpi_object arg = { ACPI_TYPE_INTEGER };
 349         struct acpi_object_list arg_list = { 1, &arg };
 350         acpi_status status = AE_OK;
 351         int i;
 352         int ret = 0;
 353
 354
 355         if (!dev || !dev->wakeup.flags.valid)
 356                 return -1;
 357
 358         arg.integer.value = 0;
 359         /* Execute PSW */
 360         status = acpi_evaluate_object(dev->handle, "_PSW", &arg_list, NULL);
 361         if (ACPI_FAILURE(status) && (status != AE_NOT_FOUND)) {
 362                 printk(KERN_ERR PREFIX "Evaluate _PSW\n");
 363                 dev->wakeup.flags.valid = 0;
 364                 return -1;
 365         }
 366
 367         /* Close power resource */
 368         for (i = 0; i < dev->wakeup.resources.count; i++) {
 369                 ret = acpi_power_off_device(dev->wakeup.resources.handles[i], dev);
 370                 if (ret) {
 371                         printk(KERN_ERR PREFIX "Transition power state\n");
 372                         dev->wakeup.flags.valid = 0;
 373                         return -1;
 374                 }
 375         }
 376
 377         return ret;
 378 }
 379
 380 /* --------------------------------------------------------------------------
 381                              Device Power Management
 382    -------------------------------------------------------------------------- */
 383
 384 int acpi_power_get_inferred_state(struct acpi_device *device)
 385 {
 386         int result = 0;
 387         struct acpi_handle_list *list = NULL;
 388         int list_state = 0;
 389         int i = 0;
 390
 391
 392         if (!device)
 393                 return -EINVAL;
 394
 395         device->power.state = ACPI_STATE_UNKNOWN;
 396
 397         /*
 398          * We know a device's inferred power state when all the resources
 399          * required for a given D-state are 'on'.
 400          */
 401         for (i = ACPI_STATE_D0; i < ACPI_STATE_D3; i++) {
 402                 list = &device->power.states[i].resources;
 403                 if (list->count < 1)
 404                         continue;
 405
 406                 result = acpi_power_get_list_state(list, &list_state);
 407                 if (result)
 408                         return result;
 409
 410                 if (list_state == ACPI_POWER_RESOURCE_STATE_ON) {
 411                         device->power.state = i;
 412                         return 0;
 413                 }
 414         }
 415
 416         device->power.state = ACPI_STATE_D3;
 417
 418         return 0;
 419 }
 420
 421 int acpi_power_transition(struct acpi_device *device, int state)
 422 {
 423         int result = 0;
 424         struct acpi_handle_list *cl = NULL;     /* Current Resources */
 425         struct acpi_handle_list *tl = NULL;     /* Target Resources */
 426         int i = 0;
 427
 428
 429         if (!device || (state < ACPI_STATE_D0) || (state > ACPI_STATE_D3))
 430                 return -EINVAL;
 431
 432         if ((device->power.state < ACPI_STATE_D0)
 433             || (device->power.state > ACPI_STATE_D3))
 434                 return -ENODEV;
 435
 436         cl = &device->power.states[device->power.state].resources;
 437         tl = &device->power.states[state].resources;
 438
 439         if (!cl->count && !tl->count) {
 440                 result = -ENODEV;
 441                 goto end;
 442         }
 443
 444         /* TBD: Resources must be ordered. */
 445
 446         /*
 447          * First we reference all power resources required in the target list
 448          * (e.g. so the device doesn't lose power while transitioning).
 449          */
 450         for (i = 0; i < tl->count; i++) {
 451                 result = acpi_power_on(tl->handles[i], device);
 452                 if (result)
 453                         goto end;
 454         }
 455
 456         if (device->power.state == state) {
 457                 goto end;
 458         }
 459
 460         /*
 461          * Then we dereference all power resources used in the current list.
 462          */
 463         for (i = 0; i < cl->count; i++) {
 464                 result = acpi_power_off_device(cl->handles[i], device);
 465                 if (result)
 466                         goto end;
 467         }
 468
 469      end:
 470         if (result) {
 471                 device->power.state = ACPI_STATE_UNKNOWN;
 472                 printk(KERN_WARNING PREFIX "Transitioning device [%s] to D%d\n",
 473                               device->pnp.bus_id, state);
 474         } else {
 475         /* We shouldn't change the state till all above operations succeed */
 476                 device->power.state = state;
 477         }
 478
 479         return result;
 480 }
 481
 482 /* --------------------------------------------------------------------------
 483                               FS Interface (/proc)
 484    -------------------------------------------------------------------------- */
 485
 486 static struct proc_dir_entry *acpi_power_dir;
 487
 488 static int acpi_power_seq_show(struct seq_file *seq, void *offset)
 489 {
 490         int count = 0;
 491         int result = 0;
 492         struct acpi_power_resource *resource = NULL;
 493         struct list_head *node, *next;
 494         struct acpi_power_reference *ref;
 495
 496
 497         resource = seq->private;
 498
 499         if (!resource)
 500                 goto end;
 501
 502         result = acpi_power_get_state(resource);
 503         if (result)
 504                 goto end;
 505
 506         seq_puts(seq, "state:                   ");
 507         switch (resource->state) {
 508         case ACPI_POWER_RESOURCE_STATE_ON:
 509                 seq_puts(seq, "on\n");
 510                 break;
 511         case ACPI_POWER_RESOURCE_STATE_OFF:
 512                 seq_puts(seq, "off\n");
 513                 break;
 514         default:
 515                 seq_puts(seq, "unknown\n");
 516                 break;
 517         }
 518
 519         mutex_lock(&resource->resource_lock);
 520         list_for_each_safe(node, next, &resource->reference) {
 521                 ref = container_of(node, struct acpi_power_reference, node);
 522                 count++;
 523         }
 524         mutex_unlock(&resource->resource_lock);
 525
 526         seq_printf(seq, "system level:            S%d\n"
 527                    "order:                   %d\n"
 528                    "reference count:         %d\n",
 529                    resource->system_level,
 530                    resource->order, count);
 531
 532       end:
 533         return 0;
 534 }
 535
 536 static int acpi_power_open_fs(struct inode *inode, struct file *file)
 537 {
 538         return single_open(file, acpi_power_seq_show, PDE(inode)->data);
 539 }
 540
 541 static int acpi_power_add_fs(struct acpi_device *device)
 542 {
 543         struct proc_dir_entry *entry = NULL;
 544
 545
 546         if (!device)
 547                 return -EINVAL;
 548
 549         if (!acpi_device_dir(device)) {
 550                 acpi_device_dir(device) = proc_mkdir(acpi_device_bid(device),
 551                                                      acpi_power_dir);
 552                 if (!acpi_device_dir(device))
 553                         return -ENODEV;
 554         }
 555
 556         /* 'status' [R] */
 557         entry = create_proc_entry(ACPI_POWER_FILE_STATUS,
 558                                   S_IRUGO, acpi_device_dir(device));
 559         if (!entry)
 560                 return -EIO;
 561         else {
 562                 entry->proc_fops = &acpi_power_fops;
 563                 entry->data = acpi_driver_data(device);
 564         }
 565
 566         return 0;
 567 }
 568
 569 static int acpi_power_remove_fs(struct acpi_device *device)
 570 {
 571
 572         if (acpi_device_dir(device)) {
 573                 remove_proc_entry(ACPI_POWER_FILE_STATUS,
 574                                   acpi_device_dir(device));
 575                 remove_proc_entry(acpi_device_bid(device), acpi_power_dir);
 576                 acpi_device_dir(device) = NULL;
 577         }
 578
 579         return 0;
 580 }
 581
 582 /* --------------------------------------------------------------------------
 583                                 Driver Interface
 584    -------------------------------------------------------------------------- */
 585
 586 static int acpi_power_add(struct acpi_device *device)
 587 {
 588         int result = 0;
 589         acpi_status status = AE_OK;
 590         struct acpi_power_resource *resource = NULL;
 591         union acpi_object acpi_object;
 592         struct acpi_buffer buffer = { sizeof(acpi_object), &acpi_object };
 593
 594
 595         if (!device)
 596                 return -EINVAL;
 597
 598         resource = kzalloc(sizeof(struct acpi_power_resource), GFP_KERNEL);
 599         if (!resource)
 600                 return -ENOMEM;
 601
 602         resource->device = device;
 603         mutex_init(&resource->resource_lock);
 604         INIT_LIST_HEAD(&resource->reference);
 605         strcpy(resource->name, device->pnp.bus_id);
 606         strcpy(acpi_device_name(device), ACPI_POWER_DEVICE_NAME);
 607         strcpy(acpi_device_class(device), ACPI_POWER_CLASS);
 608         acpi_driver_data(device) = resource;
 609
 610         /* Evalute the object to get the system level and resource order. */
 611         status = acpi_evaluate_object(device->handle, NULL, NULL, &buffer);
 612         if (ACPI_FAILURE(status)) {
 613                 result = -ENODEV;
 614                 goto end;
 615         }
 616         resource->system_level = acpi_object.power_resource.system_level;
 617         resource->order = acpi_object.power_resource.resource_order;
 618
 619         result = acpi_power_get_state(resource);
 620         if (result)
 621                 goto end;
 622
 623         switch (resource->state) {
 624         case ACPI_POWER_RESOURCE_STATE_ON:
 625                 device->power.state = ACPI_STATE_D0;
 626                 break;
 627         case ACPI_POWER_RESOURCE_STATE_OFF:
 628                 device->power.state = ACPI_STATE_D3;
 629                 break;
 630         default:
 631                 device->power.state = ACPI_STATE_UNKNOWN;
 632                 break;
 633         }
 634
 635         result = acpi_power_add_fs(device);
 636         if (result)
 637                 goto end;
 638
 639         printk(KERN_INFO PREFIX "%s [%s] (%s)\n", acpi_device_name(device),
 640                acpi_device_bid(device), resource->state ? "on" : "off");
 641
 642       end:
 643         if (result)
 644                 kfree(resource);
 645
 646         return result;
 647 }
 648
 649 static int acpi_power_remove(struct acpi_device *device, int type)
 650 {
 651         struct acpi_power_resource *resource = NULL;
 652         struct list_head *node, *next;
 653
 654
 655         if (!device || !acpi_driver_data(device))
 656                 return -EINVAL;
 657
 658         resource = acpi_driver_data(device);
 659
 660         acpi_power_remove_fs(device);
 661
 662         mutex_lock(&resource->resource_lock);
 663         list_for_each_safe(node, next, &resource->reference) {
 664                 struct acpi_power_reference *ref = container_of(node, struct acpi_power_reference, node);
 665                 list_del(&ref->node);
 666                 kfree(ref);
 667         }
 668         mutex_unlock(&resource->resource_lock);
 669
 670         kfree(resource);
 671
 672         return 0;
 673 }
 674
 675 static int acpi_power_resume(struct acpi_device *device)
 676 {
 677         int result = 0;
 678         struct acpi_power_resource *resource = NULL;
 679         struct acpi_power_reference *ref;
 680
 681         if (!device || !acpi_driver_data(device))
 682                 return -EINVAL;
 683
 684         resource = (struct acpi_power_resource *)acpi_driver_data(device);
 685
 686         result = acpi_power_get_state(resource);
 687         if (result)
 688                 return result;
 689
 690         mutex_lock(&resource->resource_lock);
 691         if ((resource->state == ACPI_POWER_RESOURCE_STATE_OFF) &&
 692             !list_empty(&resource->reference)) {
 693                 ref = container_of(resource->reference.next, struct acpi_power_reference, node);
 694                 mutex_unlock(&resource->resource_lock);
 695                 result = acpi_power_on(device->handle, ref->device);
 696                 return result;
 697         }
 698
 699         mutex_unlock(&resource->resource_lock);
 700         return 0;
 701 }
 702
 703 static int __init acpi_power_init(void)
 704 {
 705         int result = 0;
 706
 707
 708         if (acpi_disabled)
 709                 return 0;
 710
 711         INIT_LIST_HEAD(&acpi_power_resource_list);
 712
 713         acpi_power_dir = proc_mkdir(ACPI_POWER_CLASS, acpi_root_dir);
 714         if (!acpi_power_dir)
 715                 return -ENODEV;
 716
 717         result = acpi_bus_register_driver(&acpi_power_driver);
 718         if (result < 0) {
 719                 remove_proc_entry(ACPI_POWER_CLASS, acpi_root_dir);
 720                 return -ENODEV;
 721         }
 722
 723         return 0;
 724 }
 725
 726 subsys_initcall(acpi_power_init);