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 is sleeping, will not add\n",
  79                                 dev->parent->bus_id);
  80                         WARN_ON(true);
  81                 }
  82         } else if (transition_started) {
  83                 /*
  84                  * We refuse to register parentless devices while a PM
  85                  * transition is in progress in order to avoid leaving them
  86                  * unhandled down the road
  87                  */
  88                 WARN_ON(true);
  89         }
  90
  91         list_add_tail(&dev->power.entry, &dpm_list);
  92         mutex_unlock(&dpm_list_mtx);
  93 }
  94
  95 /**
  96  *      device_pm_remove - remove a device from the list of active devices
  97  *      @dev:   Device to be removed from the list
  98  *
  99  *      This function also removes the device's PM-related sysfs attributes.
 100  */
 101 void device_pm_remove(struct device *dev)
 102 {
 103         pr_debug("PM: Removing info for %s:%s\n",
 104                  dev->bus ? dev->bus->name : "No Bus",
 105                  kobject_name(&dev->kobj));
 106         mutex_lock(&dpm_list_mtx);
 107         list_del_init(&dev->power.entry);
 108         mutex_unlock(&dpm_list_mtx);
 109 }
 110
 111 /**
 112  *      pm_op - execute the PM operation appropiate for given PM event
 113  *      @dev:   Device.
 114  *      @ops:   PM operations to choose from.
 115  *      @state: PM transition of the system being carried out.
 116  */
 117 static int pm_op(struct device *dev, struct pm_ops *ops, pm_message_t state)
 118 {
 119         int error = 0;
 120
 121         switch (state.event) {
 122 #ifdef CONFIG_SUSPEND
 123         case PM_EVENT_SUSPEND:
 124                 if (ops->suspend) {
 125                         error = ops->suspend(dev);
 126                         suspend_report_result(ops->suspend, error);
 127                 }
 128                 break;
 129         case PM_EVENT_RESUME:
 130                 if (ops->resume) {
 131                         error = ops->resume(dev);
 132                         suspend_report_result(ops->resume, error);
 133                 }
 134                 break;
 135 #endif /* CONFIG_SUSPEND */
 136 #ifdef CONFIG_HIBERNATION
 137         case PM_EVENT_FREEZE:
 138         case PM_EVENT_QUIESCE:
 139                 if (ops->freeze) {
 140                         error = ops->freeze(dev);
 141                         suspend_report_result(ops->freeze, error);
 142                 }
 143                 break;
 144         case PM_EVENT_HIBERNATE:
 145                 if (ops->poweroff) {
 146                         error = ops->poweroff(dev);
 147                         suspend_report_result(ops->poweroff, error);
 148                 }
 149                 break;
 150         case PM_EVENT_THAW:
 151         case PM_EVENT_RECOVER:
 152                 if (ops->thaw) {
 153                         error = ops->thaw(dev);
 154                         suspend_report_result(ops->thaw, error);
 155                 }
 156                 break;
 157         case PM_EVENT_RESTORE:
 158                 if (ops->restore) {
 159                         error = ops->restore(dev);
 160                         suspend_report_result(ops->restore, error);
 161                 }
 162                 break;
 163 #endif /* CONFIG_HIBERNATION */
 164         default:
 165                 error = -EINVAL;
 166         }
 167         return error;
 168 }
 169
 170 /**
 171  *      pm_noirq_op - execute the PM operation appropiate for given PM event
 172  *      @dev:   Device.
 173  *      @ops:   PM operations to choose from.
 174  *      @state: PM transition of the system being carried out.
 175  *
 176  *      The operation is executed with interrupts disabled by the only remaining
 177  *      functional CPU in the system.
 178  */
 179 static int pm_noirq_op(struct device *dev, struct pm_ext_ops *ops,
 180                         pm_message_t state)
 181 {
 182         int error = 0;
 183
 184         switch (state.event) {
 185 #ifdef CONFIG_SUSPEND
 186         case PM_EVENT_SUSPEND:
 187                 if (ops->suspend_noirq) {
 188                         error = ops->suspend_noirq(dev);
 189                         suspend_report_result(ops->suspend_noirq, error);
 190                 }
 191                 break;
 192         case PM_EVENT_RESUME:
 193                 if (ops->resume_noirq) {
 194                         error = ops->resume_noirq(dev);
 195                         suspend_report_result(ops->resume_noirq, error);
 196                 }
 197                 break;
 198 #endif /* CONFIG_SUSPEND */
 199 #ifdef CONFIG_HIBERNATION
 200         case PM_EVENT_FREEZE:
 201         case PM_EVENT_QUIESCE:
 202                 if (ops->freeze_noirq) {
 203                         error = ops->freeze_noirq(dev);
 204                         suspend_report_result(ops->freeze_noirq, error);
 205                 }
 206                 break;
 207         case PM_EVENT_HIBERNATE:
 208                 if (ops->poweroff_noirq) {
 209                         error = ops->poweroff_noirq(dev);
 210                         suspend_report_result(ops->poweroff_noirq, error);
 211                 }
 212                 break;
 213         case PM_EVENT_THAW:
 214         case PM_EVENT_RECOVER:
 215                 if (ops->thaw_noirq) {
 216                         error = ops->thaw_noirq(dev);
 217                         suspend_report_result(ops->thaw_noirq, error);
 218                 }
 219                 break;
 220         case PM_EVENT_RESTORE:
 221                 if (ops->restore_noirq) {
 222                         error = ops->restore_noirq(dev);
 223                         suspend_report_result(ops->restore_noirq, error);
 224                 }
 225                 break;
 226 #endif /* CONFIG_HIBERNATION */
 227         default:
 228                 error = -EINVAL;
 229         }
 230         return error;
 231 }
 232
 233 static char *pm_verb(int event)
 234 {
 235         switch (event) {
 236         case PM_EVENT_SUSPEND:
 237                 return "suspend";
 238         case PM_EVENT_RESUME:
 239                 return "resume";
 240         case PM_EVENT_FREEZE:
 241                 return "freeze";
 242         case PM_EVENT_QUIESCE:
 243                 return "quiesce";
 244         case PM_EVENT_HIBERNATE:
 245                 return "hibernate";
 246         case PM_EVENT_THAW:
 247                 return "thaw";
 248         case PM_EVENT_RESTORE:
 249                 return "restore";
 250         case PM_EVENT_RECOVER:
 251                 return "recover";
 252         default:
 253                 return "(unknown PM event)";
 254         }
 255 }
 256
 257 static void pm_dev_dbg(struct device *dev, pm_message_t state, char *info)
 258 {
 259         dev_dbg(dev, "%s%s%s\n", info, pm_verb(state.event),
 260                 ((state.event & PM_EVENT_SLEEP) && device_may_wakeup(dev)) ?
 261                 ", may wakeup" : "");
 262 }
 263
 264 static void pm_dev_err(struct device *dev, pm_message_t state, char *info,
 265                         int error)
 266 {
 267         printk(KERN_ERR "PM: Device %s failed to %s%s: error %d\n",
 268                 kobject_name(&dev->kobj), pm_verb(state.event), info, error);
 269 }
 270
 271 /*------------------------- Resume routines -------------------------*/
 272
 273 /**
 274  *      resume_device_noirq - Power on one device (early resume).
 275  *      @dev:   Device.
 276  *      @state: PM transition of the system being carried out.
 277  *
 278  *      Must be called with interrupts disabled.
 279  */
 280 static int resume_device_noirq(struct device *dev, pm_message_t state)
 281 {
 282         int error = 0;
 283
 284         TRACE_DEVICE(dev);
 285         TRACE_RESUME(0);
 286
 287         if (!dev->bus)
 288                 goto End;
 289
 290         if (dev->bus->pm) {
 291                 pm_dev_dbg(dev, state, "EARLY ");
 292                 error = pm_noirq_op(dev, dev->bus->pm, state);
 293         } else if (dev->bus->resume_early) {
 294                 pm_dev_dbg(dev, state, "legacy EARLY ");
 295                 error = dev->bus->resume_early(dev);
 296         }
 297  End:
 298         TRACE_RESUME(error);
 299         return error;
 300 }
 301
 302 /**
 303  *      dpm_power_up - Power on all regular (non-sysdev) devices.
 304  *      @state: PM transition of the system being carried out.
 305  *
 306  *      Execute the appropriate "noirq resume" callback for all devices marked
 307  *      as DPM_OFF_IRQ.
 308  *
 309  *      Must be called with interrupts disabled and only one CPU running.
 310  */
 311 static void dpm_power_up(pm_message_t state)
 312 {
 313         struct device *dev;
 314
 315         list_for_each_entry(dev, &dpm_list, power.entry)
 316                 if (dev->power.status > DPM_OFF) {
 317                         int error;
 318
 319                         dev->power.status = DPM_OFF;
 320                         error = resume_device_noirq(dev, state);
 321                         if (error)
 322                                 pm_dev_err(dev, state, " early", error);
 323                 }
 324 }
 325
 326 /**
 327  *      device_power_up - Turn on all devices that need special attention.
 328  *      @state: PM transition of the system being carried out.
 329  *
 330  *      Power on system devices, then devices that required we shut them down
 331  *      with interrupts disabled.
 332  *
 333  *      Must be called with interrupts disabled.
 334  */
 335 void device_power_up(pm_message_t state)
 336 {
 337         sysdev_resume();
 338         dpm_power_up(state);
 339 }
 340 EXPORT_SYMBOL_GPL(device_power_up);
 341
 342 /**
 343  *      resume_device - Restore state for one device.
 344  *      @dev:   Device.
 345  *      @state: PM transition of the system being carried out.
 346  */
 347 static int resume_device(struct device *dev, pm_message_t state)
 348 {
 349         int error = 0;
 350
 351         TRACE_DEVICE(dev);
 352         TRACE_RESUME(0);
 353
 354         down(&dev->sem);
 355
 356         if (dev->bus) {
 357                 if (dev->bus->pm) {
 358                         pm_dev_dbg(dev, state, "");
 359                         error = pm_op(dev, &dev->bus->pm->base, state);
 360                 } else if (dev->bus->resume) {
 361                         pm_dev_dbg(dev, state, "legacy ");
 362                         error = dev->bus->resume(dev);
 363                 }
 364                 if (error)
 365                         goto End;
 366         }
 367
 368         if (dev->type) {
 369                 if (dev->type->pm) {
 370                         pm_dev_dbg(dev, state, "type ");
 371                         error = pm_op(dev, dev->type->pm, state);
 372                 } else if (dev->type->resume) {
 373                         pm_dev_dbg(dev, state, "legacy type ");
 374                         error = dev->type->resume(dev);
 375                 }
 376                 if (error)
 377                         goto End;
 378         }
 379
 380         if (dev->class) {
 381                 if (dev->class->pm) {
 382                         pm_dev_dbg(dev, state, "class ");
 383                         error = pm_op(dev, dev->class->pm, state);
 384                 } else if (dev->class->resume) {
 385                         pm_dev_dbg(dev, state, "legacy class ");
 386                         error = dev->class->resume(dev);
 387                 }
 388         }
 389  End:
 390         up(&dev->sem);
 391
 392         TRACE_RESUME(error);
 393         return error;
 394 }
 395
 396 /**
 397  *      dpm_resume - Resume every device.
 398  *      @state: PM transition of the system being carried out.
 399  *
 400  *      Execute the appropriate "resume" callback for all devices the status of
 401  *      which indicates that they are inactive.
 402  */
 403 static void dpm_resume(pm_message_t state)
 404 {
 405         struct list_head list;
 406
 407         INIT_LIST_HEAD(&list);
 408         mutex_lock(&dpm_list_mtx);
 409         transition_started = false;
 410         while (!list_empty(&dpm_list)) {
 411                 struct device *dev = to_device(dpm_list.next);
 412
 413                 get_device(dev);
 414                 if (dev->power.status >= DPM_OFF) {
 415                         int error;
 416
 417                         dev->power.status = DPM_RESUMING;
 418                         mutex_unlock(&dpm_list_mtx);
 419
 420                         error = resume_device(dev, state);
 421
 422                         mutex_lock(&dpm_list_mtx);
 423                         if (error)
 424                                 pm_dev_err(dev, state, "", error);
 425                 } else if (dev->power.status == DPM_SUSPENDING) {
 426                         /* Allow new children of the device to be registered */
 427                         dev->power.status = DPM_RESUMING;
 428                 }
 429                 if (!list_empty(&dev->power.entry))
 430                         list_move_tail(&dev->power.entry, &list);
 431                 put_device(dev);
 432         }
 433         list_splice(&list, &dpm_list);
 434         mutex_unlock(&dpm_list_mtx);
 435 }
 436
 437 /**
 438  *      complete_device - Complete a PM transition for given device
 439  *      @dev:   Device.
 440  *      @state: PM transition of the system being carried out.
 441  */
 442 static void complete_device(struct device *dev, pm_message_t state)
 443 {
 444         down(&dev->sem);
 445
 446         if (dev->class && dev->class->pm && dev->class->pm->complete) {
 447                 pm_dev_dbg(dev, state, "completing class ");
 448                 dev->class->pm->complete(dev);
 449         }
 450
 451         if (dev->type && dev->type->pm && dev->type->pm->complete) {
 452                 pm_dev_dbg(dev, state, "completing type ");
 453                 dev->type->pm->complete(dev);
 454         }
 455
 456         if (dev->bus && dev->bus->pm && dev->bus->pm->base.complete) {
 457                 pm_dev_dbg(dev, state, "completing ");
 458                 dev->bus->pm->base.complete(dev);
 459         }
 460
 461         up(&dev->sem);
 462 }
 463
 464 /**
 465  *      dpm_complete - Complete a PM transition for all devices.
 466  *      @state: PM transition of the system being carried out.
 467  *
 468  *      Execute the ->complete() callbacks for all devices that are not marked
 469  *      as DPM_ON.
 470  */
 471 static void dpm_complete(pm_message_t state)
 472 {
 473         struct list_head list;
 474
 475         INIT_LIST_HEAD(&list);
 476         mutex_lock(&dpm_list_mtx);
 477         while (!list_empty(&dpm_list)) {
 478                 struct device *dev = to_device(dpm_list.prev);
 479
 480                 get_device(dev);
 481                 if (dev->power.status > DPM_ON) {
 482                         dev->power.status = DPM_ON;
 483                         mutex_unlock(&dpm_list_mtx);
 484
 485                         complete_device(dev, state);
 486
 487                         mutex_lock(&dpm_list_mtx);
 488                 }
 489                 if (!list_empty(&dev->power.entry))
 490                         list_move(&dev->power.entry, &list);
 491                 put_device(dev);
 492         }
 493         list_splice(&list, &dpm_list);
 494         mutex_unlock(&dpm_list_mtx);
 495 }
 496
 497 /**
 498  *      device_resume - Restore state of each device in system.
 499  *      @state: PM transition of the system being carried out.
 500  *
 501  *      Resume all the devices, unlock them all, and allow new
 502  *      devices to be registered once again.
 503  */
 504 void device_resume(pm_message_t state)
 505 {
 506         might_sleep();
 507         dpm_resume(state);
 508         dpm_complete(state);
 509 }
 510 EXPORT_SYMBOL_GPL(device_resume);
 511
 512
 513 /*------------------------- Suspend routines -------------------------*/
 514
 515 /**
 516  *      resume_event - return a PM message representing the resume event
 517  *                     corresponding to given sleep state.
 518  *      @sleep_state: PM message representing a sleep state.
 519  */
 520 static pm_message_t resume_event(pm_message_t sleep_state)
 521 {
 522         switch (sleep_state.event) {
 523         case PM_EVENT_SUSPEND:
 524                 return PMSG_RESUME;
 525         case PM_EVENT_FREEZE:
 526         case PM_EVENT_QUIESCE:
 527                 return PMSG_RECOVER;
 528         case PM_EVENT_HIBERNATE:
 529                 return PMSG_RESTORE;
 530         }
 531         return PMSG_ON;
 532 }
 533
 534 /**
 535  *      suspend_device_noirq - Shut down one device (late suspend).
 536  *      @dev:   Device.
 537  *      @state: PM transition of the system being carried out.
 538  *
 539  *      This is called with interrupts off and only a single CPU running.
 540  */
 541 static int suspend_device_noirq(struct device *dev, pm_message_t state)
 542 {
 543         int error = 0;
 544
 545         if (!dev->bus)
 546                 return 0;
 547
 548         if (dev->bus->pm) {
 549                 pm_dev_dbg(dev, state, "LATE ");
 550                 error = pm_noirq_op(dev, dev->bus->pm, state);
 551         } else if (dev->bus->suspend_late) {
 552                 pm_dev_dbg(dev, state, "legacy LATE ");
 553                 error = dev->bus->suspend_late(dev, state);
 554                 suspend_report_result(dev->bus->suspend_late, error);
 555         }
 556         return error;
 557 }
 558
 559 /**
 560  *      device_power_down - Shut down special devices.
 561  *      @state: PM transition of the system being carried out.
 562  *
 563  *      Power down devices that require interrupts to be disabled.
 564  *      Then power down system devices.
 565  *
 566  *      Must be called with interrupts disabled and only one CPU running.
 567  */
 568 int device_power_down(pm_message_t state)
 569 {
 570         struct device *dev;
 571         int error = 0;
 572
 573         list_for_each_entry_reverse(dev, &dpm_list, power.entry) {
 574                 error = suspend_device_noirq(dev, state);
 575                 if (error) {
 576                         pm_dev_err(dev, state, " late", error);
 577                         break;
 578                 }
 579                 dev->power.status = DPM_OFF_IRQ;
 580         }
 581         if (!error)
 582                 error = sysdev_suspend(state);
 583         if (error)
 584                 dpm_power_up(resume_event(state));
 585         return error;
 586 }
 587 EXPORT_SYMBOL_GPL(device_power_down);
 588
 589 /**
 590  *      suspend_device - Save state of one device.
 591  *      @dev:   Device.
 592  *      @state: PM transition of the system being carried out.
 593  */
 594 static int suspend_device(struct device *dev, pm_message_t state)
 595 {
 596         int error = 0;
 597
 598         down(&dev->sem);
 599
 600         if (dev->class) {
 601                 if (dev->class->pm) {
 602                         pm_dev_dbg(dev, state, "class ");
 603                         error = pm_op(dev, dev->class->pm, state);
 604                 } else if (dev->class->suspend) {
 605                         pm_dev_dbg(dev, state, "legacy class ");
 606                         error = dev->class->suspend(dev, state);
 607                         suspend_report_result(dev->class->suspend, error);
 608                 }
 609                 if (error)
 610                         goto End;
 611         }
 612
 613         if (dev->type) {
 614                 if (dev->type->pm) {
 615                         pm_dev_dbg(dev, state, "type ");
 616                         error = pm_op(dev, dev->type->pm, state);
 617                 } else if (dev->type->suspend) {
 618                         pm_dev_dbg(dev, state, "legacy type ");
 619                         error = dev->type->suspend(dev, state);
 620                         suspend_report_result(dev->type->suspend, error);
 621                 }
 622                 if (error)
 623                         goto End;
 624         }
 625
 626         if (dev->bus) {
 627                 if (dev->bus->pm) {
 628                         pm_dev_dbg(dev, state, "");
 629                         error = pm_op(dev, &dev->bus->pm->base, state);
 630                 } else if (dev->bus->suspend) {
 631                         pm_dev_dbg(dev, state, "legacy ");
 632                         error = dev->bus->suspend(dev, state);
 633                         suspend_report_result(dev->bus->suspend, error);
 634                 }
 635         }
 636  End:
 637         up(&dev->sem);
 638
 639         return error;
 640 }
 641
 642 /**
 643  *      dpm_suspend - Suspend every device.
 644  *      @state: PM transition of the system being carried out.
 645  *
 646  *      Execute the appropriate "suspend" callbacks for all devices.
 647  */
 648 static int dpm_suspend(pm_message_t state)
 649 {
 650         struct list_head list;
 651         int error = 0;
 652
 653         INIT_LIST_HEAD(&list);
 654         mutex_lock(&dpm_list_mtx);
 655         while (!list_empty(&dpm_list)) {
 656                 struct device *dev = to_device(dpm_list.prev);
 657
 658                 get_device(dev);
 659                 mutex_unlock(&dpm_list_mtx);
 660
 661                 error = suspend_device(dev, state);
 662
 663                 mutex_lock(&dpm_list_mtx);
 664                 if (error) {
 665                         pm_dev_err(dev, state, "", error);
 666                         put_device(dev);
 667                         break;
 668                 }
 669                 dev->power.status = DPM_OFF;
 670                 if (!list_empty(&dev->power.entry))
 671                         list_move(&dev->power.entry, &list);
 672                 put_device(dev);
 673         }
 674         list_splice(&list, dpm_list.prev);
 675         mutex_unlock(&dpm_list_mtx);
 676         return error;
 677 }
 678
 679 /**
 680  *      prepare_device - Execute the ->prepare() callback(s) for given device.
 681  *      @dev:   Device.
 682  *      @state: PM transition of the system being carried out.
 683  */
 684 static int prepare_device(struct device *dev, pm_message_t state)
 685 {
 686         int error = 0;
 687
 688         down(&dev->sem);
 689
 690         if (dev->bus && dev->bus->pm && dev->bus->pm->base.prepare) {
 691                 pm_dev_dbg(dev, state, "preparing ");
 692                 error = dev->bus->pm->base.prepare(dev);
 693                 suspend_report_result(dev->bus->pm->base.prepare, error);
 694                 if (error)
 695                         goto End;
 696         }
 697
 698         if (dev->type && dev->type->pm && dev->type->pm->prepare) {
 699                 pm_dev_dbg(dev, state, "preparing type ");
 700                 error = dev->type->pm->prepare(dev);
 701                 suspend_report_result(dev->type->pm->prepare, error);
 702                 if (error)
 703                         goto End;
 704         }
 705
 706         if (dev->class && dev->class->pm && dev->class->pm->prepare) {
 707                 pm_dev_dbg(dev, state, "preparing class ");
 708                 error = dev->class->pm->prepare(dev);
 709                 suspend_report_result(dev->class->pm->prepare, error);
 710         }
 711  End:
 712         up(&dev->sem);
 713
 714         return error;
 715 }
 716
 717 /**
 718  *      dpm_prepare - Prepare all devices for a PM transition.
 719  *      @state: PM transition of the system being carried out.
 720  *
 721  *      Execute the ->prepare() callback for all devices.
 722  */
 723 static int dpm_prepare(pm_message_t state)
 724 {
 725         struct list_head list;
 726         int error = 0;
 727
 728         INIT_LIST_HEAD(&list);
 729         mutex_lock(&dpm_list_mtx);
 730         transition_started = true;
 731         while (!list_empty(&dpm_list)) {
 732                 struct device *dev = to_device(dpm_list.next);
 733
 734                 get_device(dev);
 735                 dev->power.status = DPM_PREPARING;
 736                 mutex_unlock(&dpm_list_mtx);
 737
 738                 error = prepare_device(dev, state);
 739
 740                 mutex_lock(&dpm_list_mtx);
 741                 if (error) {
 742                         dev->power.status = DPM_ON;
 743                         if (error == -EAGAIN) {
 744                                 put_device(dev);
 745                                 continue;
 746                         }
 747                         printk(KERN_ERR "PM: Failed to prepare device %s "
 748                                 "for power transition: error %d\n",
 749                                 kobject_name(&dev->kobj), error);
 750                         put_device(dev);
 751                         break;
 752                 }
 753                 dev->power.status = DPM_SUSPENDING;
 754                 if (!list_empty(&dev->power.entry))
 755                         list_move_tail(&dev->power.entry, &list);
 756                 put_device(dev);
 757         }
 758         list_splice(&list, &dpm_list);
 759         mutex_unlock(&dpm_list_mtx);
 760         return error;
 761 }
 762
 763 /**
 764  *      device_suspend - Save state and stop all devices in system.
 765  *      @state: PM transition of the system being carried out.
 766  *
 767  *      Prepare and suspend all devices.
 768  */
 769 int device_suspend(pm_message_t state)
 770 {
 771         int error;
 772
 773         might_sleep();
 774         error = dpm_prepare(state);
 775         if (!error)
 776                 error = dpm_suspend(state);
 777         return error;
 778 }
 779 EXPORT_SYMBOL_GPL(device_suspend);
 780
 781 void __suspend_report_result(const char *function, void *fn, int ret)
 782 {
 783         if (ret) {
 784                 printk(KERN_ERR "%s(): ", function);
 785                 print_fn_descriptor_symbol("%s returns ", fn);
 786                 printk("%d\n", ret);
 787         }
 788 }
 789 EXPORT_SYMBOL_GPL(__suspend_report_result);