kernel/time/alarmtimer.c

   1 /*
   2  * Alarmtimer interface
   3  *
   4  * This interface provides a timer which is similarto hrtimers,
   5  * but triggers a RTC alarm if the box is suspend.
   6  *
   7  * This interface is influenced by the Android RTC Alarm timer
   8  * interface.
   9  *
  10  * Copyright (C) 2010 IBM Corperation
  11  *
  12  * Author: John Stultz <john.stultz@linaro.org>
  13  *
  14  * This program is free software; you can redistribute it and/or modify
  15  * it under the terms of the GNU General Public License version 2 as
  16  * published by the Free Software Foundation.
  17  */
  18 #include <linux/time.h>
  19 #include <linux/hrtimer.h>
  20 #include <linux/timerqueue.h>
  21 #include <linux/rtc.h>
  22 #include <linux/alarmtimer.h>
  23 #include <linux/mutex.h>
  24 #include <linux/platform_device.h>
  25 #include <linux/posix-timers.h>
  26 #include <linux/workqueue.h>
  27 #include <linux/freezer.h>
  28
  29 /**
  30  * struct alarm_base - Alarm timer bases
  31  * @lock:               Lock for syncrhonized access to the base
  32  * @timerqueue:         Timerqueue head managing the list of events
  33  * @timer:              hrtimer used to schedule events while running
  34  * @gettime:            Function to read the time correlating to the base
  35  * @base_clockid:       clockid for the base
  36  */
  37 static struct alarm_base {
  38         spinlock_t              lock;
  39         struct timerqueue_head  timerqueue;
  40         struct hrtimer          timer;
  41         ktime_t                 (*gettime)(void);
  42         clockid_t               base_clockid;
  43 } alarm_bases[ALARM_NUMTYPE];
  44
  45 #ifdef CONFIG_RTC_CLASS
  46 /* rtc timer and device for setting alarm wakeups at suspend */
  47 static struct rtc_timer         rtctimer;
  48 static struct rtc_device        *rtcdev;
  49 #endif
  50
  51 /* freezer delta & lock used to handle clock_nanosleep triggered wakeups */
  52 static ktime_t freezer_delta;
  53 static DEFINE_SPINLOCK(freezer_delta_lock);
  54
  55
  56 /**
  57  * alarmtimer_enqueue - Adds an alarm timer to an alarm_base timerqueue
  58  * @base: pointer to the base where the timer is being run
  59  * @alarm: pointer to alarm being enqueued.
  60  *
  61  * Adds alarm to a alarm_base timerqueue and if necessary sets
  62  * an hrtimer to run.
  63  *
  64  * Must hold base->lock when calling.
  65  */
  66 static void alarmtimer_enqueue(struct alarm_base *base, struct alarm *alarm)
  67 {
  68         timerqueue_add(&base->timerqueue, &alarm->node);
  69         if (&alarm->node == timerqueue_getnext(&base->timerqueue)) {
  70                 hrtimer_try_to_cancel(&base->timer);
  71                 hrtimer_start(&base->timer, alarm->node.expires,
  72                                 HRTIMER_MODE_ABS);
  73         }
  74 }
  75
  76 /**
  77  * alarmtimer_remove - Removes an alarm timer from an alarm_base timerqueue
  78  * @base: pointer to the base where the timer is running
  79  * @alarm: pointer to alarm being removed
  80  *
  81  * Removes alarm to a alarm_base timerqueue and if necessary sets
  82  * a new timer to run.
  83  *
  84  * Must hold base->lock when calling.
  85  */
  86 static void alarmtimer_remove(struct alarm_base *base, struct alarm *alarm)
  87 {
  88         struct timerqueue_node *next = timerqueue_getnext(&base->timerqueue);
  89
  90         timerqueue_del(&base->timerqueue, &alarm->node);
  91         if (next == &alarm->node) {
  92                 hrtimer_try_to_cancel(&base->timer);
  93                 next = timerqueue_getnext(&base->timerqueue);
  94                 if (!next)
  95                         return;
  96                 hrtimer_start(&base->timer, next->expires, HRTIMER_MODE_ABS);
  97         }
  98 }
  99
 100
 101 /**
 102  * alarmtimer_fired - Handles alarm hrtimer being fired.
 103  * @timer: pointer to hrtimer being run
 104  *
 105  * When a alarm timer fires, this runs through the timerqueue to
 106  * see which alarms expired, and runs those. If there are more alarm
 107  * timers queued for the future, we set the hrtimer to fire when
 108  * when the next future alarm timer expires.
 109  */
 110 static enum hrtimer_restart alarmtimer_fired(struct hrtimer *timer)
 111 {
 112         struct alarm_base *base = container_of(timer, struct alarm_base, timer);
 113         struct timerqueue_node *next;
 114         unsigned long flags;
 115         ktime_t now;
 116         int ret = HRTIMER_NORESTART;
 117
 118         spin_lock_irqsave(&base->lock, flags);
 119         now = base->gettime();
 120         while ((next = timerqueue_getnext(&base->timerqueue))) {
 121                 struct alarm *alarm;
 122                 ktime_t expired = next->expires;
 123
 124                 if (expired.tv64 >= now.tv64)
 125                         break;
 126
 127                 alarm = container_of(next, struct alarm, node);
 128
 129                 timerqueue_del(&base->timerqueue, &alarm->node);
 130                 alarm->enabled = 0;
 131                 /* Re-add periodic timers */
 132                 if (alarm->period.tv64) {
 133                         alarm->node.expires = ktime_add(expired, alarm->period);
 134                         timerqueue_add(&base->timerqueue, &alarm->node);
 135                         alarm->enabled = 1;
 136                 }
 137                 spin_unlock_irqrestore(&base->lock, flags);
 138                 if (alarm->function)
 139                         alarm->function(alarm);
 140                 spin_lock_irqsave(&base->lock, flags);
 141         }
 142
 143         if (next) {
 144                 hrtimer_set_expires(&base->timer, next->expires);
 145                 ret = HRTIMER_RESTART;
 146         }
 147         spin_unlock_irqrestore(&base->lock, flags);
 148
 149         return ret;
 150
 151 }
 152
 153 #ifdef CONFIG_RTC_CLASS
 154 /**
 155  * alarmtimer_suspend - Suspend time callback
 156  * @dev: unused
 157  * @state: unused
 158  *
 159  * When we are going into suspend, we look through the bases
 160  * to see which is the soonest timer to expire. We then
 161  * set an rtc timer to fire that far into the future, which
 162  * will wake us from suspend.
 163  */
 164 static int alarmtimer_suspend(struct device *dev)
 165 {
 166         struct rtc_time tm;
 167         ktime_t min, now;
 168         unsigned long flags;
 169         int i;
 170
 171         spin_lock_irqsave(&freezer_delta_lock, flags);
 172         min = freezer_delta;
 173         freezer_delta = ktime_set(0, 0);
 174         spin_unlock_irqrestore(&freezer_delta_lock, flags);
 175
 176         /* If we have no rtcdev, just return */
 177         if (!rtcdev)
 178                 return 0;
 179
 180         /* Find the soonest timer to expire*/
 181         for (i = 0; i < ALARM_NUMTYPE; i++) {
 182                 struct alarm_base *base = &alarm_bases[i];
 183                 struct timerqueue_node *next;
 184                 ktime_t delta;
 185
 186                 spin_lock_irqsave(&base->lock, flags);
 187                 next = timerqueue_getnext(&base->timerqueue);
 188                 spin_unlock_irqrestore(&base->lock, flags);
 189                 if (!next)
 190                         continue;
 191                 delta = ktime_sub(next->expires, base->gettime());
 192                 if (!min.tv64 || (delta.tv64 < min.tv64))
 193                         min = delta;
 194         }
 195         if (min.tv64 == 0)
 196                 return 0;
 197
 198         /* XXX - Should we enforce a minimum sleep time? */
 199         WARN_ON(min.tv64 < NSEC_PER_SEC);
 200
 201         /* Setup an rtc timer to fire that far in the future */
 202         rtc_timer_cancel(rtcdev, &rtctimer);
 203         rtc_read_time(rtcdev, &tm);
 204         now = rtc_tm_to_ktime(tm);
 205         now = ktime_add(now, min);
 206
 207         rtc_timer_start(rtcdev, &rtctimer, now, ktime_set(0, 0));
 208
 209         return 0;
 210 }
 211 #else
 212 static int alarmtimer_suspend(struct device *dev)
 213 {
 214         return 0;
 215 }
 216 #endif
 217
 218 static void alarmtimer_freezerset(ktime_t absexp, enum alarmtimer_type type)
 219 {
 220         ktime_t delta;
 221         unsigned long flags;
 222         struct alarm_base *base = &alarm_bases[type];
 223
 224         delta = ktime_sub(absexp, base->gettime());
 225
 226         spin_lock_irqsave(&freezer_delta_lock, flags);
 227         if (!freezer_delta.tv64 || (delta.tv64 < freezer_delta.tv64))
 228                 freezer_delta = delta;
 229         spin_unlock_irqrestore(&freezer_delta_lock, flags);
 230 }
 231
 232
 233 /**
 234  * alarm_init - Initialize an alarm structure
 235  * @alarm: ptr to alarm to be initialized
 236  * @type: the type of the alarm
 237  * @function: callback that is run when the alarm fires
 238  */
 239 void alarm_init(struct alarm *alarm, enum alarmtimer_type type,
 240                 void (*function)(struct alarm *))
 241 {
 242         timerqueue_init(&alarm->node);
 243         alarm->period = ktime_set(0, 0);
 244         alarm->function = function;
 245         alarm->type = type;
 246         alarm->enabled = 0;
 247 }
 248
 249 /**
 250  * alarm_start - Sets an alarm to fire
 251  * @alarm: ptr to alarm to set
 252  * @start: time to run the alarm
 253  * @period: period at which the alarm will recur
 254  */
 255 void alarm_start(struct alarm *alarm, ktime_t start, ktime_t period)
 256 {
 257         struct alarm_base *base = &alarm_bases[alarm->type];
 258         unsigned long flags;
 259
 260         spin_lock_irqsave(&base->lock, flags);
 261         if (alarm->enabled)
 262                 alarmtimer_remove(base, alarm);
 263         alarm->node.expires = start;
 264         alarm->period = period;
 265         alarmtimer_enqueue(base, alarm);
 266         alarm->enabled = 1;
 267         spin_unlock_irqrestore(&base->lock, flags);
 268 }
 269
 270 /**
 271  * alarm_cancel - Tries to cancel an alarm timer
 272  * @alarm: ptr to alarm to be canceled
 273  */
 274 void alarm_cancel(struct alarm *alarm)
 275 {
 276         struct alarm_base *base = &alarm_bases[alarm->type];
 277         unsigned long flags;
 278
 279         spin_lock_irqsave(&base->lock, flags);
 280         if (alarm->enabled)
 281                 alarmtimer_remove(base, alarm);
 282         alarm->enabled = 0;
 283         spin_unlock_irqrestore(&base->lock, flags);
 284 }
 285
 286
 287 /**
 288  * clock2alarm - helper that converts from clockid to alarmtypes
 289  * @clockid: clockid.
 290  */
 291 static enum alarmtimer_type clock2alarm(clockid_t clockid)
 292 {
 293         if (clockid == CLOCK_REALTIME_ALARM)
 294                 return ALARM_REALTIME;
 295         if (clockid == CLOCK_BOOTTIME_ALARM)
 296                 return ALARM_BOOTTIME;
 297         return -1;
 298 }
 299
 300 /**
 301  * alarm_handle_timer - Callback for posix timers
 302  * @alarm: alarm that fired
 303  *
 304  * Posix timer callback for expired alarm timers.
 305  */
 306 static void alarm_handle_timer(struct alarm *alarm)
 307 {
 308         struct k_itimer *ptr = container_of(alarm, struct k_itimer,
 309                                                 it.alarmtimer);
 310         if (posix_timer_event(ptr, 0) != 0)
 311                 ptr->it_overrun++;
 312 }
 313
 314 /**
 315  * alarm_clock_getres - posix getres interface
 316  * @which_clock: clockid
 317  * @tp: timespec to fill
 318  *
 319  * Returns the granularity of underlying alarm base clock
 320  */
 321 static int alarm_clock_getres(const clockid_t which_clock, struct timespec *tp)
 322 {
 323         clockid_t baseid = alarm_bases[clock2alarm(which_clock)].base_clockid;
 324
 325         return hrtimer_get_res(baseid, tp);
 326 }
 327
 328 /**
 329  * alarm_clock_get - posix clock_get interface
 330  * @which_clock: clockid
 331  * @tp: timespec to fill.
 332  *
 333  * Provides the underlying alarm base time.
 334  */
 335 static int alarm_clock_get(clockid_t which_clock, struct timespec *tp)
 336 {
 337         struct alarm_base *base = &alarm_bases[clock2alarm(which_clock)];
 338
 339         *tp = ktime_to_timespec(base->gettime());
 340         return 0;
 341 }
 342
 343 /**
 344  * alarm_timer_create - posix timer_create interface
 345  * @new_timer: k_itimer pointer to manage
 346  *
 347  * Initializes the k_itimer structure.
 348  */
 349 static int alarm_timer_create(struct k_itimer *new_timer)
 350 {
 351         enum  alarmtimer_type type;
 352         struct alarm_base *base;
 353
 354         if (!capable(CAP_WAKE_ALARM))
 355                 return -EPERM;
 356
 357         type = clock2alarm(new_timer->it_clock);
 358         base = &alarm_bases[type];
 359         alarm_init(&new_timer->it.alarmtimer, type, alarm_handle_timer);
 360         return 0;
 361 }
 362
 363 /**
 364  * alarm_timer_get - posix timer_get interface
 365  * @new_timer: k_itimer pointer
 366  * @cur_setting: itimerspec data to fill
 367  *
 368  * Copies the itimerspec data out from the k_itimer
 369  */
 370 static void alarm_timer_get(struct k_itimer *timr,
 371                                 struct itimerspec *cur_setting)
 372 {
 373         cur_setting->it_interval =
 374                         ktime_to_timespec(timr->it.alarmtimer.period);
 375         cur_setting->it_value =
 376                         ktime_to_timespec(timr->it.alarmtimer.node.expires);
 377         return;
 378 }
 379
 380 /**
 381  * alarm_timer_del - posix timer_del interface
 382  * @timr: k_itimer pointer to be deleted
 383  *
 384  * Cancels any programmed alarms for the given timer.
 385  */
 386 static int alarm_timer_del(struct k_itimer *timr)
 387 {
 388         alarm_cancel(&timr->it.alarmtimer);
 389         return 0;
 390 }
 391
 392 /**
 393  * alarm_timer_set - posix timer_set interface
 394  * @timr: k_itimer pointer to be deleted
 395  * @flags: timer flags
 396  * @new_setting: itimerspec to be used
 397  * @old_setting: itimerspec being replaced
 398  *
 399  * Sets the timer to new_setting, and starts the timer.
 400  */
 401 static int alarm_timer_set(struct k_itimer *timr, int flags,
 402                                 struct itimerspec *new_setting,
 403                                 struct itimerspec *old_setting)
 404 {
 405         /* Save old values */
 406         old_setting->it_interval =
 407                         ktime_to_timespec(timr->it.alarmtimer.period);
 408         old_setting->it_value =
 409                         ktime_to_timespec(timr->it.alarmtimer.node.expires);
 410
 411         /* If the timer was already set, cancel it */
 412         alarm_cancel(&timr->it.alarmtimer);
 413
 414         /* start the timer */
 415         alarm_start(&timr->it.alarmtimer,
 416                         timespec_to_ktime(new_setting->it_value),
 417                         timespec_to_ktime(new_setting->it_interval));
 418         return 0;
 419 }
 420
 421 /**
 422  * alarmtimer_nsleep_wakeup - Wakeup function for alarm_timer_nsleep
 423  * @alarm: ptr to alarm that fired
 424  *
 425  * Wakes up the task that set the alarmtimer
 426  */
 427 static void alarmtimer_nsleep_wakeup(struct alarm *alarm)
 428 {
 429         struct task_struct *task = (struct task_struct *)alarm->data;
 430
 431         alarm->data = NULL;
 432         if (task)
 433                 wake_up_process(task);
 434 }
 435
 436 /**
 437  * alarmtimer_do_nsleep - Internal alarmtimer nsleep implementation
 438  * @alarm: ptr to alarmtimer
 439  * @absexp: absolute expiration time
 440  *
 441  * Sets the alarm timer and sleeps until it is fired or interrupted.
 442  */
 443 static int alarmtimer_do_nsleep(struct alarm *alarm, ktime_t absexp)
 444 {
 445         alarm->data = (void *)current;
 446         do {
 447                 set_current_state(TASK_INTERRUPTIBLE);
 448                 alarm_start(alarm, absexp, ktime_set(0, 0));
 449                 if (likely(alarm->data))
 450                         schedule();
 451
 452                 alarm_cancel(alarm);
 453         } while (alarm->data && !signal_pending(current));
 454
 455         __set_current_state(TASK_RUNNING);
 456
 457         return (alarm->data == NULL);
 458 }
 459
 460
 461 /**
 462  * update_rmtp - Update remaining timespec value
 463  * @exp: expiration time
 464  * @type: timer type
 465  * @rmtp: user pointer to remaining timepsec value
 466  *
 467  * Helper function that fills in rmtp value with time between
 468  * now and the exp value
 469  */
 470 static int update_rmtp(ktime_t exp, enum  alarmtimer_type type,
 471                         struct timespec __user *rmtp)
 472 {
 473         struct timespec rmt;
 474         ktime_t rem;
 475
 476         rem = ktime_sub(exp, alarm_bases[type].gettime());
 477
 478         if (rem.tv64 <= 0)
 479                 return 0;
 480         rmt = ktime_to_timespec(rem);
 481
 482         if (copy_to_user(rmtp, &rmt, sizeof(*rmtp)))
 483                 return -EFAULT;
 484
 485         return 1;
 486
 487 }
 488
 489 /**
 490  * alarm_timer_nsleep_restart - restartblock alarmtimer nsleep
 491  * @restart: ptr to restart block
 492  *
 493  * Handles restarted clock_nanosleep calls
 494  */
 495 static long __sched alarm_timer_nsleep_restart(struct restart_block *restart)
 496 {
 497         enum  alarmtimer_type type = restart->nanosleep.clockid;
 498         ktime_t exp;
 499         struct timespec __user  *rmtp;
 500         struct alarm alarm;
 501         int ret = 0;
 502
 503         exp.tv64 = restart->nanosleep.expires;
 504         alarm_init(&alarm, type, alarmtimer_nsleep_wakeup);
 505
 506         if (alarmtimer_do_nsleep(&alarm, exp))
 507                 goto out;
 508
 509         if (freezing(current))
 510                 alarmtimer_freezerset(exp, type);
 511
 512         rmtp = restart->nanosleep.rmtp;
 513         if (rmtp) {
 514                 ret = update_rmtp(exp, type, rmtp);
 515                 if (ret <= 0)
 516                         goto out;
 517         }
 518
 519
 520         /* The other values in restart are already filled in */
 521         ret = -ERESTART_RESTARTBLOCK;
 522 out:
 523         return ret;
 524 }
 525
 526 /**
 527  * alarm_timer_nsleep - alarmtimer nanosleep
 528  * @which_clock: clockid
 529  * @flags: determins abstime or relative
 530  * @tsreq: requested sleep time (abs or rel)
 531  * @rmtp: remaining sleep time saved
 532  *
 533  * Handles clock_nanosleep calls against _ALARM clockids
 534  */
 535 static int alarm_timer_nsleep(const clockid_t which_clock, int flags,
 536                      struct timespec *tsreq, struct timespec __user *rmtp)
 537 {
 538         enum  alarmtimer_type type = clock2alarm(which_clock);
 539         struct alarm alarm;
 540         ktime_t exp;
 541         int ret = 0;
 542         struct restart_block *restart;
 543
 544         if (!capable(CAP_WAKE_ALARM))
 545                 return -EPERM;
 546
 547         alarm_init(&alarm, type, alarmtimer_nsleep_wakeup);
 548
 549         exp = timespec_to_ktime(*tsreq);
 550         /* Convert (if necessary) to absolute time */
 551         if (flags != TIMER_ABSTIME) {
 552                 ktime_t now = alarm_bases[type].gettime();
 553                 exp = ktime_add(now, exp);
 554         }
 555
 556         if (alarmtimer_do_nsleep(&alarm, exp))
 557                 goto out;
 558
 559         if (freezing(current))
 560                 alarmtimer_freezerset(exp, type);
 561
 562         /* abs timers don't set remaining time or restart */
 563         if (flags == TIMER_ABSTIME) {
 564                 ret = -ERESTARTNOHAND;
 565                 goto out;
 566         }
 567
 568         if (rmtp) {
 569                 ret = update_rmtp(exp, type, rmtp);
 570                 if (ret <= 0)
 571                         goto out;
 572         }
 573
 574         restart = &current_thread_info()->restart_block;
 575         restart->fn = alarm_timer_nsleep_restart;
 576         restart->nanosleep.clockid = type;
 577         restart->nanosleep.expires = exp.tv64;
 578         restart->nanosleep.rmtp = rmtp;
 579         ret = -ERESTART_RESTARTBLOCK;
 580
 581 out:
 582         return ret;
 583 }
 584
 585
 586 /* Suspend hook structures */
 587 static const struct dev_pm_ops alarmtimer_pm_ops = {
 588         .suspend = alarmtimer_suspend,
 589 };
 590
 591 static struct platform_driver alarmtimer_driver = {
 592         .driver = {
 593                 .name = "alarmtimer",
 594                 .pm = &alarmtimer_pm_ops,
 595         }
 596 };
 597
 598 /**
 599  * alarmtimer_init - Initialize alarm timer code
 600  *
 601  * This function initializes the alarm bases and registers
 602  * the posix clock ids.
 603  */
 604 static int __init alarmtimer_init(void)
 605 {
 606         int error = 0;
 607         int i;
 608         struct k_clock alarm_clock = {
 609                 .clock_getres   = alarm_clock_getres,
 610                 .clock_get      = alarm_clock_get,
 611                 .timer_create   = alarm_timer_create,
 612                 .timer_set      = alarm_timer_set,
 613                 .timer_del      = alarm_timer_del,
 614                 .timer_get      = alarm_timer_get,
 615                 .nsleep         = alarm_timer_nsleep,
 616         };
 617
 618         posix_timers_register_clock(CLOCK_REALTIME_ALARM, &alarm_clock);
 619         posix_timers_register_clock(CLOCK_BOOTTIME_ALARM, &alarm_clock);
 620
 621         /* Initialize alarm bases */
 622         alarm_bases[ALARM_REALTIME].base_clockid = CLOCK_REALTIME;
 623         alarm_bases[ALARM_REALTIME].gettime = &ktime_get_real;
 624         alarm_bases[ALARM_BOOTTIME].base_clockid = CLOCK_BOOTTIME;
 625         alarm_bases[ALARM_BOOTTIME].gettime = &ktime_get_boottime;
 626         for (i = 0; i < ALARM_NUMTYPE; i++) {
 627                 timerqueue_init_head(&alarm_bases[i].timerqueue);
 628                 spin_lock_init(&alarm_bases[i].lock);
 629                 hrtimer_init(&alarm_bases[i].timer,
 630                                 alarm_bases[i].base_clockid,
 631                                 HRTIMER_MODE_ABS);
 632                 alarm_bases[i].timer.function = alarmtimer_fired;
 633         }
 634         error = platform_driver_register(&alarmtimer_driver);
 635         platform_device_register_simple("alarmtimer", -1, NULL, 0);
 636
 637         return error;
 638 }
 639 device_initcall(alarmtimer_init);
 640
 641 #ifdef CONFIG_RTC_CLASS
 642 /**
 643  * has_wakealarm - check rtc device has wakealarm ability
 644  * @dev: current device
 645  * @name_ptr: name to be returned
 646  *
 647  * This helper function checks to see if the rtc device can wake
 648  * from suspend.
 649  */
 650 static int __init has_wakealarm(struct device *dev, void *name_ptr)
 651 {
 652         struct rtc_device *candidate = to_rtc_device(dev);
 653
 654         if (!candidate->ops->set_alarm)
 655                 return 0;
 656         if (!device_may_wakeup(candidate->dev.parent))
 657                 return 0;
 658
 659         *(const char **)name_ptr = dev_name(dev);
 660         return 1;
 661 }
 662
 663 /**
 664  * alarmtimer_init_late - Late initializing of alarmtimer code
 665  *
 666  * This function locates a rtc device to use for wakealarms.
 667  * Run as late_initcall to make sure rtc devices have been
 668  * registered.
 669  */
 670 static int __init alarmtimer_init_late(void)
 671 {
 672         struct device *dev;
 673         char *str;
 674
 675         /* Find an rtc device and init the rtc_timer */
 676         dev = class_find_device(rtc_class, NULL, &str, has_wakealarm);
 677         /* If we have a device then str is valid. See has_wakealarm() */
 678         if (dev) {
 679                 rtcdev = rtc_class_open(str);
 680                 /*
 681                  * Drop the reference we got in class_find_device,
 682                  * rtc_open takes its own.
 683                  */
 684                 put_device(dev);
 685         }
 686         if (!rtcdev) {
 687                 printk(KERN_WARNING "No RTC device found, ALARM timers will"
 688                         " not wake from suspend");
 689         }
 690         rtc_timer_init(&rtctimer, NULL, NULL);
 691
 692         return 0;
 693 }
 694 #else
 695 static int __init alarmtimer_init_late(void)
 696 {
 697         printk(KERN_WARNING "Kernel not built with RTC support, ALARM timers"
 698                 " will not wake from suspend");
 699         return 0;
 700 }
 701 #endif
 702 late_initcall(alarmtimer_init_late);