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                 WARN_ON(true);
  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         check_for_bios_corruption();
 258         dev_dbg(dev, "%s%s%s\n", info, pm_verb(state.event),
 259                 ((state.event & PM_EVENT_SLEEP) && device_may_wakeup(dev)) ?
 260                 ", may wakeup" : "");
 261 }
 262
 263 static void pm_dev_err(struct device *dev, pm_message_t state, char *info,
 264                         int error)
 265 {
 266         printk(KERN_ERR "PM: Device %s failed to %s%s: error %d\n",
 267                 kobject_name(&dev->kobj), pm_verb(state.event), info, error);
 268 }
 269
 270 /*------------------------- Resume routines -------------------------*/
 271
 272 /**
 273  *      resume_device_noirq - Power on one device (early resume).
 274  *      @dev:   Device.
 275  *      @state: PM transition of the system being carried out.
 276  *
 277  *      Must be called with interrupts disabled.
 278  */
 279 static int resume_device_noirq(struct device *dev, pm_message_t state)
 280 {
 281         int error = 0;
 282
 283         TRACE_DEVICE(dev);
 284         TRACE_RESUME(0);
 285
 286         if (!dev->bus)
 287                 goto End;
 288
 289         if (dev->bus->pm) {
 290                 pm_dev_dbg(dev, state, "EARLY ");
 291                 error = pm_noirq_op(dev, dev->bus->pm, state);
 292         } else if (dev->bus->resume_early) {
 293                 pm_dev_dbg(dev, state, "legacy EARLY ");
 294                 error = dev->bus->resume_early(dev);
 295         }
 296  End:
 297         TRACE_RESUME(error);
 298         return error;
 299 }
 300
 301 /**
 302  *      dpm_power_up - Power on all regular (non-sysdev) devices.
 303  *      @state: PM transition of the system being carried out.
 304  *
 305  *      Execute the appropriate "noirq resume" callback for all devices marked
 306  *      as DPM_OFF_IRQ.
 307  *
 308  *      Must be called with interrupts disabled and only one CPU running.
 309  */
 310 static void dpm_power_up(pm_message_t state)
 311 {
 312         struct device *dev;
 313
 314         list_for_each_entry(dev, &dpm_list, power.entry)
 315                 if (dev->power.status > DPM_OFF) {
 316                         int error;
 317
 318                         dev->power.status = DPM_OFF;
 319                         error = resume_device_noirq(dev, state);
 320                         if (error)
 321                                 pm_dev_err(dev, state, " early", error);
 322                 }
 323 }
 324
 325 /**
 326  *      device_power_up - Turn on all devices that need special attention.
 327  *      @state: PM transition of the system being carried out.
 328  *
 329  *      Power on system devices, then devices that required we shut them down
 330  *      with interrupts disabled.
 331  *
 332  *      Must be called with interrupts disabled.
 333  */
 334 void device_power_up(pm_message_t state)
 335 {
 336         sysdev_resume();
 337         dpm_power_up(state);
 338 }
 339 EXPORT_SYMBOL_GPL(device_power_up);
 340
 341 /**
 342  *      resume_device - Restore state for one device.
 343  *      @dev:   Device.
 344  *      @state: PM transition of the system being carried out.
 345  */
 346 static int resume_device(struct device *dev, pm_message_t state)
 347 {
 348         int error = 0;
 349
 350         TRACE_DEVICE(dev);
 351         TRACE_RESUME(0);
 352
 353         down(&dev->sem);
 354
 355         if (dev->bus) {
 356                 if (dev->bus->pm) {
 357                         pm_dev_dbg(dev, state, "");
 358                         error = pm_op(dev, &dev->bus->pm->base, state);
 359                 } else if (dev->bus->resume) {
 360                         pm_dev_dbg(dev, state, "legacy ");
 361                         error = dev->bus->resume(dev);
 362                 }
 363                 if (error)
 364                         goto End;
 365         }
 366
 367         if (dev->type) {
 368                 if (dev->type->pm) {
 369                         pm_dev_dbg(dev, state, "type ");
 370                         error = pm_op(dev, dev->type->pm, state);
 371                 } else if (dev->type->resume) {
 372                         pm_dev_dbg(dev, state, "legacy type ");
 373                         error = dev->type->resume(dev);
 374                 }
 375                 if (error)
 376                         goto End;
 377         }
 378
 379         if (dev->class) {
 380                 if (dev->class->pm) {
 381                         pm_dev_dbg(dev, state, "class ");
 382                         error = pm_op(dev, dev->class->pm, state);
 383                 } else if (dev->class->resume) {
 384                         pm_dev_dbg(dev, state, "legacy class ");
 385                         error = dev->class->resume(dev);
 386                 }
 387         }
 388  End:
 389         up(&dev->sem);
 390
 391         TRACE_RESUME(error);
 392         return error;
 393 }
 394
 395 /**
 396  *      dpm_resume - Resume every device.
 397  *      @state: PM transition of the system being carried out.
 398  *
 399  *      Execute the appropriate "resume" callback for all devices the status of
 400  *      which indicates that they are inactive.
 401  */
 402 static void dpm_resume(pm_message_t state)
 403 {
 404         struct list_head list;
 405
 406         INIT_LIST_HEAD(&list);
 407         mutex_lock(&dpm_list_mtx);
 408         transition_started = false;
 409         while (!list_empty(&dpm_list)) {
 410                 struct device *dev = to_device(dpm_list.next);
 411
 412                 get_device(dev);
 413                 if (dev->power.status >= DPM_OFF) {
 414                         int error;
 415
 416                         dev->power.status = DPM_RESUMING;
 417                         mutex_unlock(&dpm_list_mtx);
 418
 419                         error = resume_device(dev, state);
 420
 421                         mutex_lock(&dpm_list_mtx);
 422                         if (error)
 423                                 pm_dev_err(dev, state, "", error);
 424                 } else if (dev->power.status == DPM_SUSPENDING) {
 425                         /* Allow new children of the device to be registered */
 426                         dev->power.status = DPM_RESUMING;
 427                 }
 428                 if (!list_empty(&dev->power.entry))
 429                         list_move_tail(&dev->power.entry, &list);
 430                 put_device(dev);
 431         }
 432         list_splice(&list, &dpm_list);
 433         mutex_unlock(&dpm_list_mtx);
 434 }
 435
 436 /**
 437  *      complete_device - Complete a PM transition for given device
 438  *      @dev:   Device.
 439  *      @state: PM transition of the system being carried out.
 440  */
 441 static void complete_device(struct device *dev, pm_message_t state)
 442 {
 443         down(&dev->sem);
 444
 445         if (dev->class && dev->class->pm && dev->class->pm->complete) {
 446                 pm_dev_dbg(dev, state, "completing class ");
 447                 dev->class->pm->complete(dev);
 448         }
 449
 450         if (dev->type && dev->type->pm && dev->type->pm->complete) {
 451                 pm_dev_dbg(dev, state, "completing type ");
 452                 dev->type->pm->complete(dev);
 453         }
 454
 455         if (dev->bus && dev->bus->pm && dev->bus->pm->base.complete) {
 456                 pm_dev_dbg(dev, state, "completing ");
 457                 dev->bus->pm->base.complete(dev);
 458         }
 459
 460         up(&dev->sem);
 461 }
 462
 463 /**
 464  *      dpm_complete - Complete a PM transition for all devices.
 465  *      @state: PM transition of the system being carried out.
 466  *
 467  *      Execute the ->complete() callbacks for all devices that are not marked
 468  *      as DPM_ON.
 469  */
 470 static void dpm_complete(pm_message_t state)
 471 {
 472         struct list_head list;
 473
 474         INIT_LIST_HEAD(&list);
 475         mutex_lock(&dpm_list_mtx);
 476         while (!list_empty(&dpm_list)) {
 477                 struct device *dev = to_device(dpm_list.prev);
 478
 479                 get_device(dev);
 480                 if (dev->power.status > DPM_ON) {
 481                         dev->power.status = DPM_ON;
 482                         mutex_unlock(&dpm_list_mtx);
 483
 484                         complete_device(dev, state);
 485
 486                         mutex_lock(&dpm_list_mtx);
 487                 }
 488                 if (!list_empty(&dev->power.entry))
 489                         list_move(&dev->power.entry, &list);
 490                 put_device(dev);
 491         }
 492         list_splice(&list, &dpm_list);
 493         mutex_unlock(&dpm_list_mtx);
 494 }
 495
 496 /**
 497  *      device_resume - Restore state of each device in system.
 498  *      @state: PM transition of the system being carried out.
 499  *
 500  *      Resume all the devices, unlock them all, and allow new
 501  *      devices to be registered once again.
 502  */
 503 void device_resume(pm_message_t state)
 504 {
 505         might_sleep();
 506         dpm_resume(state);
 507         dpm_complete(state);
 508 }
 509 EXPORT_SYMBOL_GPL(device_resume);
 510
 511
 512 /*------------------------- Suspend routines -------------------------*/
 513
 514 /**
 515  *      resume_event - return a PM message representing the resume event
 516  *                     corresponding to given sleep state.
 517  *      @sleep_state: PM message representing a sleep state.
 518  */
 519 static pm_message_t resume_event(pm_message_t sleep_state)
 520 {
 521         switch (sleep_state.event) {
 522         case PM_EVENT_SUSPEND:
 523                 return PMSG_RESUME;
 524         case PM_EVENT_FREEZE:
 525         case PM_EVENT_QUIESCE:
 526                 return PMSG_RECOVER;
 527         case PM_EVENT_HIBERNATE:
 528                 return PMSG_RESTORE;
 529         }
 530         return PMSG_ON;
 531 }
 532
 533 /**
 534  *      suspend_device_noirq - Shut down one device (late suspend).
 535  *      @dev:   Device.
 536  *      @state: PM transition of the system being carried out.
 537  *
 538  *      This is called with interrupts off and only a single CPU running.
 539  */
 540 static int suspend_device_noirq(struct device *dev, pm_message_t state)
 541 {
 542         int error = 0;
 543
 544         if (!dev->bus)
 545                 return 0;
 546
 547         if (dev->bus->pm) {
 548                 pm_dev_dbg(dev, state, "LATE ");
 549                 error = pm_noirq_op(dev, dev->bus->pm, state);
 550         } else if (dev->bus->suspend_late) {
 551                 pm_dev_dbg(dev, state, "legacy LATE ");
 552                 error = dev->bus->suspend_late(dev, state);
 553                 suspend_report_result(dev->bus->suspend_late, error);
 554         }
 555         return error;
 556 }
 557
 558 /**
 559  *      device_power_down - Shut down special devices.
 560  *      @state: PM transition of the system being carried out.
 561  *
 562  *      Power down devices that require interrupts to be disabled.
 563  *      Then power down system devices.
 564  *
 565  *      Must be called with interrupts disabled and only one CPU running.
 566  */
 567 int device_power_down(pm_message_t state)
 568 {
 569         struct device *dev;
 570         int error = 0;
 571
 572         list_for_each_entry_reverse(dev, &dpm_list, power.entry) {
 573                 error = suspend_device_noirq(dev, state);
 574                 if (error) {
 575                         pm_dev_err(dev, state, " late", error);
 576                         break;
 577                 }
 578                 dev->power.status = DPM_OFF_IRQ;
 579         }
 580         if (!error)
 581                 error = sysdev_suspend(state);
 582         if (error)
 583                 dpm_power_up(resume_event(state));
 584         return error;
 585 }
 586 EXPORT_SYMBOL_GPL(device_power_down);
 587
 588 /**
 589  *      suspend_device - Save state of one device.
 590  *      @dev:   Device.
 591  *      @state: PM transition of the system being carried out.
 592  */
 593 static int suspend_device(struct device *dev, pm_message_t state)
 594 {
 595         int error = 0;
 596
 597         down(&dev->sem);
 598
 599         if (dev->class) {
 600                 if (dev->class->pm) {
 601                         pm_dev_dbg(dev, state, "class ");
 602                         error = pm_op(dev, dev->class->pm, state);
 603                 } else if (dev->class->suspend) {
 604                         pm_dev_dbg(dev, state, "legacy class ");
 605                         error = dev->class->suspend(dev, state);
 606                         suspend_report_result(dev->class->suspend, error);
 607                 }
 608                 if (error)
 609                         goto End;
 610         }
 611
 612         if (dev->type) {
 613                 if (dev->type->pm) {
 614                         pm_dev_dbg(dev, state, "type ");
 615                         error = pm_op(dev, dev->type->pm, state);
 616                 } else if (dev->type->suspend) {
 617                         pm_dev_dbg(dev, state, "legacy type ");
 618                         error = dev->type->suspend(dev, state);
 619                         suspend_report_result(dev->type->suspend, error);
 620                 }
 621                 if (error)
 622                         goto End;
 623         }
 624
 625         if (dev->bus) {
 626                 if (dev->bus->pm) {
 627                         pm_dev_dbg(dev, state, "");
 628                         error = pm_op(dev, &dev->bus->pm->base, state);
 629                 } else if (dev->bus->suspend) {
 630                         pm_dev_dbg(dev, state, "legacy ");
 631                         error = dev->bus->suspend(dev, state);
 632                         suspend_report_result(dev->bus->suspend, error);
 633                 }
 634         }
 635  End:
 636         up(&dev->sem);
 637
 638         return error;
 639 }
 640
 641 /**
 642  *      dpm_suspend - Suspend every device.
 643  *      @state: PM transition of the system being carried out.
 644  *
 645  *      Execute the appropriate "suspend" callbacks for all devices.
 646  */
 647 static int dpm_suspend(pm_message_t state)
 648 {
 649         struct list_head list;
 650         int error = 0;
 651
 652         INIT_LIST_HEAD(&list);
 653         mutex_lock(&dpm_list_mtx);
 654         while (!list_empty(&dpm_list)) {
 655                 struct device *dev = to_device(dpm_list.prev);
 656
 657                 get_device(dev);
 658                 mutex_unlock(&dpm_list_mtx);
 659
 660                 error = suspend_device(dev, state);
 661
 662                 mutex_lock(&dpm_list_mtx);
 663                 if (error) {
 664                         pm_dev_err(dev, state, "", error);
 665                         put_device(dev);
 666                         break;
 667                 }
 668                 dev->power.status = DPM_OFF;
 669                 if (!list_empty(&dev->power.entry))
 670                         list_move(&dev->power.entry, &list);
 671                 put_device(dev);
 672         }
 673         list_splice(&list, dpm_list.prev);
 674         mutex_unlock(&dpm_list_mtx);
 675         return error;
 676 }
 677
 678 /**
 679  *      prepare_device - Execute the ->prepare() callback(s) for given device.
 680  *      @dev:   Device.
 681  *      @state: PM transition of the system being carried out.
 682  */
 683 static int prepare_device(struct device *dev, pm_message_t state)
 684 {
 685         int error = 0;
 686
 687         down(&dev->sem);
 688
 689         if (dev->bus && dev->bus->pm && dev->bus->pm->base.prepare) {
 690                 pm_dev_dbg(dev, state, "preparing ");
 691                 error = dev->bus->pm->base.prepare(dev);
 692                 suspend_report_result(dev->bus->pm->base.prepare, error);
 693                 if (error)
 694                         goto End;
 695         }
 696
 697         if (dev->type && dev->type->pm && dev->type->pm->prepare) {
 698                 pm_dev_dbg(dev, state, "preparing type ");
 699                 error = dev->type->pm->prepare(dev);
 700                 suspend_report_result(dev->type->pm->prepare, error);
 701                 if (error)
 702                         goto End;
 703         }
 704
 705         if (dev->class && dev->class->pm && dev->class->pm->prepare) {
 706                 pm_dev_dbg(dev, state, "preparing class ");
 707                 error = dev->class->pm->prepare(dev);
 708                 suspend_report_result(dev->class->pm->prepare, error);
 709         }
 710  End:
 711         up(&dev->sem);
 712
 713         return error;
 714 }
 715
 716 /**
 717  *      dpm_prepare - Prepare all devices for a PM transition.
 718  *      @state: PM transition of the system being carried out.
 719  *
 720  *      Execute the ->prepare() callback for all devices.
 721  */
 722 static int dpm_prepare(pm_message_t state)
 723 {
 724         struct list_head list;
 725         int error = 0;
 726
 727         INIT_LIST_HEAD(&list);
 728         mutex_lock(&dpm_list_mtx);
 729         transition_started = true;
 730         while (!list_empty(&dpm_list)) {
 731                 struct device *dev = to_device(dpm_list.next);
 732
 733                 get_device(dev);
 734                 dev->power.status = DPM_PREPARING;
 735                 mutex_unlock(&dpm_list_mtx);
 736
 737                 error = prepare_device(dev, state);
 738
 739                 mutex_lock(&dpm_list_mtx);
 740                 if (error) {
 741                         dev->power.status = DPM_ON;
 742                         if (error == -EAGAIN) {
 743                                 put_device(dev);
 744                                 continue;
 745                         }
 746                         printk(KERN_ERR "PM: Failed to prepare device %s "
 747                                 "for power transition: error %d\n",
 748                                 kobject_name(&dev->kobj), error);
 749                         put_device(dev);
 750                         break;
 751                 }
 752                 dev->power.status = DPM_SUSPENDING;
 753                 if (!list_empty(&dev->power.entry))
 754                         list_move_tail(&dev->power.entry, &list);
 755                 put_device(dev);
 756         }
 757         list_splice(&list, &dpm_list);
 758         mutex_unlock(&dpm_list_mtx);
 759         return error;
 760 }
 761
 762 /**
 763  *      device_suspend - Save state and stop all devices in system.
 764  *      @state: PM transition of the system being carried out.
 765  *
 766  *      Prepare and suspend all devices.
 767  */
 768 int device_suspend(pm_message_t state)
 769 {
 770         int error;
 771
 772         might_sleep();
 773         error = dpm_prepare(state);
 774         if (!error)
 775                 error = dpm_suspend(state);
 776         return error;
 777 }
 778 EXPORT_SYMBOL_GPL(device_suspend);
 779
 780 void __suspend_report_result(const char *function, void *fn, int ret)
 781 {
 782         if (ret) {
 783                 printk(KERN_ERR "%s(): ", function);
 784                 print_fn_descriptor_symbol("%s returns ", fn);
 785                 printk("%d\n", ret);
 786         }
 787 }
 788 EXPORT_SYMBOL_GPL(__suspend_report_result);