drivers/base/power/main.c

   1 /*
   2  * drivers/base/power/main.c - Where the driver meets power management.
   3  *
   4  * Copyright (c) 2003 Patrick Mochel
   5  * Copyright (c) 2003 Open Source Development Lab
   6  *
   7  * This file is released under the GPLv2
   8  *
   9  *
  10  * The driver model core calls device_pm_add() when a device is registered.
  11  * This will intialize the embedded device_pm_info object in the device
  12  * and add it to the list of power-controlled devices. sysfs entries for
  13  * controlling device power management will also be added.
  14  *
  15  * A separate list is used for keeping track of power info, because the power
  16  * domain dependencies may differ from the ancestral dependencies that the
  17  * subsystem list maintains.
  18  */
  19
  20 #include <linux/device.h>
  21 #include <linux/kallsyms.h>
  22 #include <linux/mutex.h>
  23 #include <linux/pm.h>
  24 #include <linux/resume-trace.h>
  25 #include <linux/rwsem.h>
  26
  27 #include "../base.h"
  28 #include "power.h"
  29
  30 /*
  31  * The entries in the dpm_list list are in a depth first order, simply
  32  * because children are guaranteed to be discovered after parents, and
  33  * are inserted at the back of the list on discovery.
  34  *
  35  * Since device_pm_add() may be called with a device semaphore held,
  36  * we must never try to acquire a device semaphore while holding
  37  * dpm_list_mutex.
  38  */
  39
  40 LIST_HEAD(dpm_list);
  41
  42 static DEFINE_MUTEX(dpm_list_mtx);
  43
  44 /*
  45  * Set once the preparation of devices for a PM transition has started, reset
  46  * before starting to resume devices.  Protected by dpm_list_mtx.
  47  */
  48 static bool transition_started;
  49
  50 /**
  51  *      device_pm_lock - lock the list of active devices used by the PM core
  52  */
  53 void device_pm_lock(void)
  54 {
  55         mutex_lock(&dpm_list_mtx);
  56 }
  57
  58 /**
  59  *      device_pm_unlock - unlock the list of active devices used by the PM core
  60  */
  61 void device_pm_unlock(void)
  62 {
  63         mutex_unlock(&dpm_list_mtx);
  64 }
  65
  66 /**
  67  *      device_pm_add - add a device to the list of active devices
  68  *      @dev:   Device to be added to the list
  69  */
  70 void device_pm_add(struct device *dev)
  71 {
  72         pr_debug("PM: Adding info for %s:%s\n",
  73                  dev->bus ? dev->bus->name : "No Bus",
  74                  kobject_name(&dev->kobj));
  75         mutex_lock(&dpm_list_mtx);
  76         if (dev->parent) {
  77                 if (dev->parent->power.status >= DPM_SUSPENDING)
  78                         dev_warn(dev, "parent %s should not be sleeping\n",
  79                                 dev->parent->bus_id);
  80         } else if (transition_started) {
  81                 /*
  82                  * We refuse to register parentless devices while a PM
  83                  * transition is in progress in order to avoid leaving them
  84                  * unhandled down the road
  85                  */
  86                 dev_WARN(dev, "Parentless device registered during a PM transaction\n");
  87         }
  88
  89         list_add_tail(&dev->power.entry, &dpm_list);
  90         mutex_unlock(&dpm_list_mtx);
  91 }
  92
  93 /**
  94  *      device_pm_remove - remove a device from the list of active devices
  95  *      @dev:   Device to be removed from the list
  96  *
  97  *      This function also removes the device's PM-related sysfs attributes.
  98  */
  99 void device_pm_remove(struct device *dev)
 100 {
 101         pr_debug("PM: Removing info for %s:%s\n",
 102                  dev->bus ? dev->bus->name : "No Bus",
 103                  kobject_name(&dev->kobj));
 104         mutex_lock(&dpm_list_mtx);
 105         list_del_init(&dev->power.entry);
 106         mutex_unlock(&dpm_list_mtx);
 107 }
 108
 109 /**
 110  *      pm_op - execute the PM operation appropiate for given PM event
 111  *      @dev:   Device.
 112  *      @ops:   PM operations to choose from.
 113  *      @state: PM transition of the system being carried out.
 114  */
 115 static int pm_op(struct device *dev, struct pm_ops *ops, pm_message_t state)
 116 {
 117         int error = 0;
 118
 119         switch (state.event) {
 120 #ifdef CONFIG_SUSPEND
 121         case PM_EVENT_SUSPEND:
 122                 if (ops->suspend) {
 123                         error = ops->suspend(dev);
 124                         suspend_report_result(ops->suspend, error);
 125                 }
 126                 break;
 127         case PM_EVENT_RESUME:
 128                 if (ops->resume) {
 129                         error = ops->resume(dev);
 130                         suspend_report_result(ops->resume, error);
 131                 }
 132                 break;
 133 #endif /* CONFIG_SUSPEND */
 134 #ifdef CONFIG_HIBERNATION
 135         case PM_EVENT_FREEZE:
 136         case PM_EVENT_QUIESCE:
 137                 if (ops->freeze) {
 138                         error = ops->freeze(dev);
 139                         suspend_report_result(ops->freeze, error);
 140                 }
 141                 break;
 142         case PM_EVENT_HIBERNATE:
 143                 if (ops->poweroff) {
 144                         error = ops->poweroff(dev);
 145                         suspend_report_result(ops->poweroff, error);
 146                 }
 147                 break;
 148         case PM_EVENT_THAW:
 149         case PM_EVENT_RECOVER:
 150                 if (ops->thaw) {
 151                         error = ops->thaw(dev);
 152                         suspend_report_result(ops->thaw, error);
 153                 }
 154                 break;
 155         case PM_EVENT_RESTORE:
 156                 if (ops->restore) {
 157                         error = ops->restore(dev);
 158                         suspend_report_result(ops->restore, error);
 159                 }
 160                 break;
 161 #endif /* CONFIG_HIBERNATION */
 162         default:
 163                 error = -EINVAL;
 164         }
 165         return error;
 166 }
 167
 168 /**
 169  *      pm_noirq_op - execute the PM operation appropiate for given PM event
 170  *      @dev:   Device.
 171  *      @ops:   PM operations to choose from.
 172  *      @state: PM transition of the system being carried out.
 173  *
 174  *      The operation is executed with interrupts disabled by the only remaining
 175  *      functional CPU in the system.
 176  */
 177 static int pm_noirq_op(struct device *dev, struct pm_ext_ops *ops,
 178                         pm_message_t state)
 179 {
 180         int error = 0;
 181
 182         switch (state.event) {
 183 #ifdef CONFIG_SUSPEND
 184         case PM_EVENT_SUSPEND:
 185                 if (ops->suspend_noirq) {
 186                         error = ops->suspend_noirq(dev);
 187                         suspend_report_result(ops->suspend_noirq, error);
 188                 }
 189                 break;
 190         case PM_EVENT_RESUME:
 191                 if (ops->resume_noirq) {
 192                         error = ops->resume_noirq(dev);
 193                         suspend_report_result(ops->resume_noirq, error);
 194                 }
 195                 break;
 196 #endif /* CONFIG_SUSPEND */
 197 #ifdef CONFIG_HIBERNATION
 198         case PM_EVENT_FREEZE:
 199         case PM_EVENT_QUIESCE:
 200                 if (ops->freeze_noirq) {
 201                         error = ops->freeze_noirq(dev);
 202                         suspend_report_result(ops->freeze_noirq, error);
 203                 }
 204                 break;
 205         case PM_EVENT_HIBERNATE:
 206                 if (ops->poweroff_noirq) {
 207                         error = ops->poweroff_noirq(dev);
 208                         suspend_report_result(ops->poweroff_noirq, error);
 209                 }
 210                 break;
 211         case PM_EVENT_THAW:
 212         case PM_EVENT_RECOVER:
 213                 if (ops->thaw_noirq) {
 214                         error = ops->thaw_noirq(dev);
 215                         suspend_report_result(ops->thaw_noirq, error);
 216                 }
 217                 break;
 218         case PM_EVENT_RESTORE:
 219                 if (ops->restore_noirq) {
 220                         error = ops->restore_noirq(dev);
 221                         suspend_report_result(ops->restore_noirq, error);
 222                 }
 223                 break;
 224 #endif /* CONFIG_HIBERNATION */
 225         default:
 226                 error = -EINVAL;
 227         }
 228         return error;
 229 }
 230
 231 static char *pm_verb(int event)
 232 {
 233         switch (event) {
 234         case PM_EVENT_SUSPEND:
 235                 return "suspend";
 236         case PM_EVENT_RESUME:
 237                 return "resume";
 238         case PM_EVENT_FREEZE:
 239                 return "freeze";
 240         case PM_EVENT_QUIESCE:
 241                 return "quiesce";
 242         case PM_EVENT_HIBERNATE:
 243                 return "hibernate";
 244         case PM_EVENT_THAW:
 245                 return "thaw";
 246         case PM_EVENT_RESTORE:
 247                 return "restore";
 248         case PM_EVENT_RECOVER:
 249                 return "recover";
 250         default:
 251                 return "(unknown PM event)";
 252         }
 253 }
 254
 255 static void pm_dev_dbg(struct device *dev, pm_message_t state, char *info)
 256 {
 257         dev_dbg(dev, "%s%s%s\n", info, pm_verb(state.event),
 258                 ((state.event & PM_EVENT_SLEEP) && device_may_wakeup(dev)) ?
 259                 ", may wakeup" : "");
 260 }
 261
 262 static void pm_dev_err(struct device *dev, pm_message_t state, char *info,
 263                         int error)
 264 {
 265         printk(KERN_ERR "PM: Device %s failed to %s%s: error %d\n",
 266                 kobject_name(&dev->kobj), pm_verb(state.event), info, error);
 267 }
 268
 269 /*------------------------- Resume routines -------------------------*/
 270
 271 /**
 272  *      resume_device_noirq - Power on one device (early resume).
 273  *      @dev:   Device.
 274  *      @state: PM transition of the system being carried out.
 275  *
 276  *      Must be called with interrupts disabled.
 277  */
 278 static int resume_device_noirq(struct device *dev, pm_message_t state)
 279 {
 280         int error = 0;
 281
 282         TRACE_DEVICE(dev);
 283         TRACE_RESUME(0);
 284
 285         if (!dev->bus)
 286                 goto End;
 287
 288         if (dev->bus->pm) {
 289                 pm_dev_dbg(dev, state, "EARLY ");
 290                 error = pm_noirq_op(dev, dev->bus->pm, state);
 291         } else if (dev->bus->resume_early) {
 292                 pm_dev_dbg(dev, state, "legacy EARLY ");
 293                 error = dev->bus->resume_early(dev);
 294         }
 295  End:
 296         TRACE_RESUME(error);
 297         return error;
 298 }
 299
 300 /**
 301  *      dpm_power_up - Power on all regular (non-sysdev) devices.
 302  *      @state: PM transition of the system being carried out.
 303  *
 304  *      Execute the appropriate "noirq resume" callback for all devices marked
 305  *      as DPM_OFF_IRQ.
 306  *
 307  *      Must be called with interrupts disabled and only one CPU running.
 308  */
 309 static void dpm_power_up(pm_message_t state)
 310 {
 311         struct device *dev;
 312
 313         list_for_each_entry(dev, &dpm_list, power.entry)
 314                 if (dev->power.status > DPM_OFF) {
 315                         int error;
 316
 317                         dev->power.status = DPM_OFF;
 318                         error = resume_device_noirq(dev, state);
 319                         if (error)
 320                                 pm_dev_err(dev, state, " early", error);
 321                 }
 322 }
 323
 324 /**
 325  *      device_power_up - Turn on all devices that need special attention.
 326  *      @state: PM transition of the system being carried out.
 327  *
 328  *      Power on system devices, then devices that required we shut them down
 329  *      with interrupts disabled.
 330  *
 331  *      Must be called with interrupts disabled.
 332  */
 333 void device_power_up(pm_message_t state)
 334 {
 335         sysdev_resume();
 336         dpm_power_up(state);
 337 }
 338 EXPORT_SYMBOL_GPL(device_power_up);
 339
 340 /**
 341  *      resume_device - Restore state for one device.
 342  *      @dev:   Device.
 343  *      @state: PM transition of the system being carried out.
 344  */
 345 static int resume_device(struct device *dev, pm_message_t state)
 346 {
 347         int error = 0;
 348
 349         TRACE_DEVICE(dev);
 350         TRACE_RESUME(0);
 351
 352         down(&dev->sem);
 353
 354         if (dev->bus) {
 355                 if (dev->bus->pm) {
 356                         pm_dev_dbg(dev, state, "");
 357                         error = pm_op(dev, &dev->bus->pm->base, state);
 358                 } else if (dev->bus->resume) {
 359                         pm_dev_dbg(dev, state, "legacy ");
 360                         error = dev->bus->resume(dev);
 361                 }
 362                 if (error)
 363                         goto End;
 364         }
 365
 366         if (dev->type) {
 367                 if (dev->type->pm) {
 368                         pm_dev_dbg(dev, state, "type ");
 369                         error = pm_op(dev, dev->type->pm, state);
 370                 } else if (dev->type->resume) {
 371                         pm_dev_dbg(dev, state, "legacy type ");
 372                         error = dev->type->resume(dev);
 373                 }
 374                 if (error)
 375                         goto End;
 376         }
 377
 378         if (dev->class) {
 379                 if (dev->class->pm) {
 380                         pm_dev_dbg(dev, state, "class ");
 381                         error = pm_op(dev, dev->class->pm, state);
 382                 } else if (dev->class->resume) {
 383                         pm_dev_dbg(dev, state, "legacy class ");
 384                         error = dev->class->resume(dev);
 385                 }
 386         }
 387  End:
 388         up(&dev->sem);
 389
 390         TRACE_RESUME(error);
 391         return error;
 392 }
 393
 394 /**
 395  *      dpm_resume - Resume every device.
 396  *      @state: PM transition of the system being carried out.
 397  *
 398  *      Execute the appropriate "resume" callback for all devices the status of
 399  *      which indicates that they are inactive.
 400  */
 401 static void dpm_resume(pm_message_t state)
 402 {
 403         struct list_head list;
 404
 405         INIT_LIST_HEAD(&list);
 406         mutex_lock(&dpm_list_mtx);
 407         transition_started = false;
 408         while (!list_empty(&dpm_list)) {
 409                 struct device *dev = to_device(dpm_list.next);
 410
 411                 get_device(dev);
 412                 if (dev->power.status >= DPM_OFF) {
 413                         int error;
 414
 415                         dev->power.status = DPM_RESUMING;
 416                         mutex_unlock(&dpm_list_mtx);
 417
 418                         error = resume_device(dev, state);
 419
 420                         mutex_lock(&dpm_list_mtx);
 421                         if (error)
 422                                 pm_dev_err(dev, state, "", error);
 423                 } else if (dev->power.status == DPM_SUSPENDING) {
 424                         /* Allow new children of the device to be registered */
 425                         dev->power.status = DPM_RESUMING;
 426                 }
 427                 if (!list_empty(&dev->power.entry))
 428                         list_move_tail(&dev->power.entry, &list);
 429                 put_device(dev);
 430         }
 431         list_splice(&list, &dpm_list);
 432         mutex_unlock(&dpm_list_mtx);
 433 }
 434
 435 /**
 436  *      complete_device - Complete a PM transition for given device
 437  *      @dev:   Device.
 438  *      @state: PM transition of the system being carried out.
 439  */
 440 static void complete_device(struct device *dev, pm_message_t state)
 441 {
 442         down(&dev->sem);
 443
 444         if (dev->class && dev->class->pm && dev->class->pm->complete) {
 445                 pm_dev_dbg(dev, state, "completing class ");
 446                 dev->class->pm->complete(dev);
 447         }
 448
 449         if (dev->type && dev->type->pm && dev->type->pm->complete) {
 450                 pm_dev_dbg(dev, state, "completing type ");
 451                 dev->type->pm->complete(dev);
 452         }
 453
 454         if (dev->bus && dev->bus->pm && dev->bus->pm->base.complete) {
 455                 pm_dev_dbg(dev, state, "completing ");
 456                 dev->bus->pm->base.complete(dev);
 457         }
 458
 459         up(&dev->sem);
 460 }
 461
 462 /**
 463  *      dpm_complete - Complete a PM transition for all devices.
 464  *      @state: PM transition of the system being carried out.
 465  *
 466  *      Execute the ->complete() callbacks for all devices that are not marked
 467  *      as DPM_ON.
 468  */
 469 static void dpm_complete(pm_message_t state)
 470 {
 471         struct list_head list;
 472
 473         INIT_LIST_HEAD(&list);
 474         mutex_lock(&dpm_list_mtx);
 475         while (!list_empty(&dpm_list)) {
 476                 struct device *dev = to_device(dpm_list.prev);
 477
 478                 get_device(dev);
 479                 if (dev->power.status > DPM_ON) {
 480                         dev->power.status = DPM_ON;
 481                         mutex_unlock(&dpm_list_mtx);
 482
 483                         complete_device(dev, state);
 484
 485                         mutex_lock(&dpm_list_mtx);
 486                 }
 487                 if (!list_empty(&dev->power.entry))
 488                         list_move(&dev->power.entry, &list);
 489                 put_device(dev);
 490         }
 491         list_splice(&list, &dpm_list);
 492         mutex_unlock(&dpm_list_mtx);
 493 }
 494
 495 /**
 496  *      device_resume - Restore state of each device in system.
 497  *      @state: PM transition of the system being carried out.
 498  *
 499  *      Resume all the devices, unlock them all, and allow new
 500  *      devices to be registered once again.
 501  */
 502 void device_resume(pm_message_t state)
 503 {
 504         might_sleep();
 505         dpm_resume(state);
 506         dpm_complete(state);
 507 }
 508 EXPORT_SYMBOL_GPL(device_resume);
 509
 510
 511 /*------------------------- Suspend routines -------------------------*/
 512
 513 /**
 514  *      resume_event - return a PM message representing the resume event
 515  *                     corresponding to given sleep state.
 516  *      @sleep_state: PM message representing a sleep state.
 517  */
 518 static pm_message_t resume_event(pm_message_t sleep_state)
 519 {
 520         switch (sleep_state.event) {
 521         case PM_EVENT_SUSPEND:
 522                 return PMSG_RESUME;
 523         case PM_EVENT_FREEZE:
 524         case PM_EVENT_QUIESCE:
 525                 return PMSG_RECOVER;
 526         case PM_EVENT_HIBERNATE:
 527                 return PMSG_RESTORE;
 528         }
 529         return PMSG_ON;
 530 }
 531
 532 /**
 533  *      suspend_device_noirq - Shut down one device (late suspend).
 534  *      @dev:   Device.
 535  *      @state: PM transition of the system being carried out.
 536  *
 537  *      This is called with interrupts off and only a single CPU running.
 538  */
 539 static int suspend_device_noirq(struct device *dev, pm_message_t state)
 540 {
 541         int error = 0;
 542
 543         if (!dev->bus)
 544                 return 0;
 545
 546         if (dev->bus->pm) {
 547                 pm_dev_dbg(dev, state, "LATE ");
 548                 error = pm_noirq_op(dev, dev->bus->pm, state);
 549         } else if (dev->bus->suspend_late) {
 550                 pm_dev_dbg(dev, state, "legacy LATE ");
 551                 error = dev->bus->suspend_late(dev, state);
 552                 suspend_report_result(dev->bus->suspend_late, error);
 553         }
 554         return error;
 555 }
 556
 557 /**
 558  *      device_power_down - Shut down special devices.
 559  *      @state: PM transition of the system being carried out.
 560  *
 561  *      Power down devices that require interrupts to be disabled.
 562  *      Then power down system devices.
 563  *
 564  *      Must be called with interrupts disabled and only one CPU running.
 565  */
 566 int device_power_down(pm_message_t state)
 567 {
 568         struct device *dev;
 569         int error = 0;
 570
 571         list_for_each_entry_reverse(dev, &dpm_list, power.entry) {
 572                 error = suspend_device_noirq(dev, state);
 573                 if (error) {
 574                         pm_dev_err(dev, state, " late", error);
 575                         break;
 576                 }
 577                 dev->power.status = DPM_OFF_IRQ;
 578         }
 579         if (!error)
 580                 error = sysdev_suspend(state);
 581         if (error)
 582                 dpm_power_up(resume_event(state));
 583         return error;
 584 }
 585 EXPORT_SYMBOL_GPL(device_power_down);
 586
 587 /**
 588  *      suspend_device - Save state of one device.
 589  *      @dev:   Device.
 590  *      @state: PM transition of the system being carried out.
 591  */
 592 static int suspend_device(struct device *dev, pm_message_t state)
 593 {
 594         int error = 0;
 595
 596         down(&dev->sem);
 597
 598         if (dev->class) {
 599                 if (dev->class->pm) {
 600                         pm_dev_dbg(dev, state, "class ");
 601                         error = pm_op(dev, dev->class->pm, state);
 602                 } else if (dev->class->suspend) {
 603                         pm_dev_dbg(dev, state, "legacy class ");
 604                         error = dev->class->suspend(dev, state);
 605                         suspend_report_result(dev->class->suspend, error);
 606                 }
 607                 if (error)
 608                         goto End;
 609         }
 610
 611         if (dev->type) {
 612                 if (dev->type->pm) {
 613                         pm_dev_dbg(dev, state, "type ");
 614                         error = pm_op(dev, dev->type->pm, state);
 615                 } else if (dev->type->suspend) {
 616                         pm_dev_dbg(dev, state, "legacy type ");
 617                         error = dev->type->suspend(dev, state);
 618                         suspend_report_result(dev->type->suspend, error);
 619                 }
 620                 if (error)
 621                         goto End;
 622         }
 623
 624         if (dev->bus) {
 625                 if (dev->bus->pm) {
 626                         pm_dev_dbg(dev, state, "");
 627                         error = pm_op(dev, &dev->bus->pm->base, state);
 628                 } else if (dev->bus->suspend) {
 629                         pm_dev_dbg(dev, state, "legacy ");
 630                         error = dev->bus->suspend(dev, state);
 631                         suspend_report_result(dev->bus->suspend, error);
 632                 }
 633         }
 634  End:
 635         up(&dev->sem);
 636
 637         return error;
 638 }
 639
 640 /**
 641  *      dpm_suspend - Suspend every device.
 642  *      @state: PM transition of the system being carried out.
 643  *
 644  *      Execute the appropriate "suspend" callbacks for all devices.
 645  */
 646 static int dpm_suspend(pm_message_t state)
 647 {
 648         struct list_head list;
 649         int error = 0;
 650
 651         INIT_LIST_HEAD(&list);
 652         mutex_lock(&dpm_list_mtx);
 653         while (!list_empty(&dpm_list)) {
 654                 struct device *dev = to_device(dpm_list.prev);
 655
 656                 get_device(dev);
 657                 mutex_unlock(&dpm_list_mtx);
 658
 659                 error = suspend_device(dev, state);
 660
 661                 mutex_lock(&dpm_list_mtx);
 662                 if (error) {
 663                         pm_dev_err(dev, state, "", error);
 664                         put_device(dev);
 665                         break;
 666                 }
 667                 dev->power.status = DPM_OFF;
 668                 if (!list_empty(&dev->power.entry))
 669                         list_move(&dev->power.entry, &list);
 670                 put_device(dev);
 671         }
 672         list_splice(&list, dpm_list.prev);
 673         mutex_unlock(&dpm_list_mtx);
 674         return error;
 675 }
 676
 677 /**
 678  *      prepare_device - Execute the ->prepare() callback(s) for given device.
 679  *      @dev:   Device.
 680  *      @state: PM transition of the system being carried out.
 681  */
 682 static int prepare_device(struct device *dev, pm_message_t state)
 683 {
 684         int error = 0;
 685
 686         down(&dev->sem);
 687
 688         if (dev->bus && dev->bus->pm && dev->bus->pm->base.prepare) {
 689                 pm_dev_dbg(dev, state, "preparing ");
 690                 error = dev->bus->pm->base.prepare(dev);
 691                 suspend_report_result(dev->bus->pm->base.prepare, error);
 692                 if (error)
 693                         goto End;
 694         }
 695
 696         if (dev->type && dev->type->pm && dev->type->pm->prepare) {
 697                 pm_dev_dbg(dev, state, "preparing type ");
 698                 error = dev->type->pm->prepare(dev);
 699                 suspend_report_result(dev->type->pm->prepare, error);
 700                 if (error)
 701                         goto End;
 702         }
 703
 704         if (dev->class && dev->class->pm && dev->class->pm->prepare) {
 705                 pm_dev_dbg(dev, state, "preparing class ");
 706                 error = dev->class->pm->prepare(dev);
 707                 suspend_report_result(dev->class->pm->prepare, error);
 708         }
 709  End:
 710         up(&dev->sem);
 711
 712         return error;
 713 }
 714
 715 /**
 716  *      dpm_prepare - Prepare all devices for a PM transition.
 717  *      @state: PM transition of the system being carried out.
 718  *
 719  *      Execute the ->prepare() callback for all devices.
 720  */
 721 static int dpm_prepare(pm_message_t state)
 722 {
 723         struct list_head list;
 724         int error = 0;
 725
 726         INIT_LIST_HEAD(&list);
 727         mutex_lock(&dpm_list_mtx);
 728         transition_started = true;
 729         while (!list_empty(&dpm_list)) {
 730                 struct device *dev = to_device(dpm_list.next);
 731
 732                 get_device(dev);
 733                 dev->power.status = DPM_PREPARING;
 734                 mutex_unlock(&dpm_list_mtx);
 735
 736                 error = prepare_device(dev, state);
 737
 738                 mutex_lock(&dpm_list_mtx);
 739                 if (error) {
 740                         dev->power.status = DPM_ON;
 741                         if (error == -EAGAIN) {
 742                                 put_device(dev);
 743                                 continue;
 744                         }
 745                         printk(KERN_ERR "PM: Failed to prepare device %s "
 746                                 "for power transition: error %d\n",
 747                                 kobject_name(&dev->kobj), error);
 748                         put_device(dev);
 749                         break;
 750                 }
 751                 dev->power.status = DPM_SUSPENDING;
 752                 if (!list_empty(&dev->power.entry))
 753                         list_move_tail(&dev->power.entry, &list);
 754                 put_device(dev);
 755         }
 756         list_splice(&list, &dpm_list);
 757         mutex_unlock(&dpm_list_mtx);
 758         return error;
 759 }
 760
 761 /**
 762  *      device_suspend - Save state and stop all devices in system.
 763  *      @state: PM transition of the system being carried out.
 764  *
 765  *      Prepare and suspend all devices.
 766  */
 767 int device_suspend(pm_message_t state)
 768 {
 769         int error;
 770
 771         might_sleep();
 772         error = dpm_prepare(state);
 773         if (!error)
 774                 error = dpm_suspend(state);
 775         return error;
 776 }
 777 EXPORT_SYMBOL_GPL(device_suspend);
 778
 779 void __suspend_report_result(const char *function, void *fn, int ret)
 780 {
 781         if (ret)
 782                 printk(KERN_ERR "%s(): %pF returns %d\n", function, fn, ret);
 783 }
 784 EXPORT_SYMBOL_GPL(__suspend_report_result);