2 * sleep.c - ACPI sleep support.
4 * Copyright (c) 2005 Alexey Starikovskiy <alexey.y.starikovskiy@intel.com>
5 * Copyright (c) 2004 David Shaohua Li <shaohua.li@intel.com>
6 * Copyright (c) 2000-2003 Patrick Mochel
7 * Copyright (c) 2003 Open Source Development Lab
9 * This file is released under the GPLv2.
13 #include <linux/delay.h>
14 #include <linux/irq.h>
15 #include <linux/dmi.h>
16 #include <linux/device.h>
17 #include <linux/suspend.h>
18 #include <linux/reboot.h>
19 #include <linux/acpi.h>
20 #include <linux/module.h>
26 static u8 sleep_states[ACPI_S_STATE_COUNT];
28 static void acpi_sleep_tts_switch(u32 acpi_state)
32 status = acpi_execute_simple_method(NULL, "\\_TTS", acpi_state);
33 if (ACPI_FAILURE(status) && status != AE_NOT_FOUND) {
35 * OS can't evaluate the _TTS object correctly. Some warning
36 * message will be printed. But it won't break anything.
38 printk(KERN_NOTICE "Failure in evaluating _TTS object\n");
42 static int tts_notify_reboot(struct notifier_block *this,
43 unsigned long code, void *x)
45 acpi_sleep_tts_switch(ACPI_STATE_S5);
49 static struct notifier_block tts_notifier = {
50 .notifier_call = tts_notify_reboot,
55 static int acpi_sleep_prepare(u32 acpi_state)
57 #ifdef CONFIG_ACPI_SLEEP
58 /* do we have a wakeup address for S2 and S3? */
59 if (acpi_state == ACPI_STATE_S3) {
60 if (!acpi_wakeup_address)
62 acpi_set_firmware_waking_vector(acpi_wakeup_address);
65 ACPI_FLUSH_CPU_CACHE();
67 printk(KERN_INFO PREFIX "Preparing to enter system sleep state S%d\n",
69 acpi_enable_wakeup_devices(acpi_state);
70 acpi_enter_sleep_state_prep(acpi_state);
74 static bool acpi_sleep_state_supported(u8 sleep_state)
79 status = acpi_get_sleep_type_data(sleep_state, &type_a, &type_b);
80 return ACPI_SUCCESS(status) && (!acpi_gbl_reduced_hardware
81 || (acpi_gbl_FADT.sleep_control.address
82 && acpi_gbl_FADT.sleep_status.address));
85 #ifdef CONFIG_ACPI_SLEEP
86 static u32 acpi_target_sleep_state = ACPI_STATE_S0;
88 u32 acpi_target_system_state(void)
90 return acpi_target_sleep_state;
92 EXPORT_SYMBOL_GPL(acpi_target_system_state);
94 static bool pwr_btn_event_pending;
97 * The ACPI specification wants us to save NVS memory regions during hibernation
98 * and to restore them during the subsequent resume. Windows does that also for
99 * suspend to RAM. However, it is known that this mechanism does not work on
100 * all machines, so we allow the user to disable it with the help of the
101 * 'acpi_sleep=nonvs' kernel command line option.
103 static bool nvs_nosave;
105 void __init acpi_nvs_nosave(void)
111 * The ACPI specification wants us to save NVS memory regions during hibernation
112 * but says nothing about saving NVS during S3. Not all versions of Windows
113 * save NVS on S3 suspend either, and it is clear that not all systems need
114 * NVS to be saved at S3 time. To improve suspend/resume time, allow the
115 * user to disable saving NVS on S3 if their system does not require it, but
116 * continue to save/restore NVS for S4 as specified.
118 static bool nvs_nosave_s3;
120 void __init acpi_nvs_nosave_s3(void)
122 nvs_nosave_s3 = true;
126 * ACPI 1.0 wants us to execute _PTS before suspending devices, so we allow the
127 * user to request that behavior by using the 'acpi_old_suspend_ordering'
128 * kernel command line option that causes the following variable to be set.
130 static bool old_suspend_ordering;
132 void __init acpi_old_suspend_ordering(void)
134 old_suspend_ordering = true;
137 static int __init init_old_suspend_ordering(const struct dmi_system_id *d)
139 acpi_old_suspend_ordering();
143 static int __init init_nvs_nosave(const struct dmi_system_id *d)
149 static struct dmi_system_id acpisleep_dmi_table[] __initdata = {
151 .callback = init_old_suspend_ordering,
152 .ident = "Abit KN9 (nForce4 variant)",
154 DMI_MATCH(DMI_BOARD_VENDOR, "http://www.abit.com.tw/"),
155 DMI_MATCH(DMI_BOARD_NAME, "KN9 Series(NF-CK804)"),
159 .callback = init_old_suspend_ordering,
160 .ident = "HP xw4600 Workstation",
162 DMI_MATCH(DMI_SYS_VENDOR, "Hewlett-Packard"),
163 DMI_MATCH(DMI_PRODUCT_NAME, "HP xw4600 Workstation"),
167 .callback = init_old_suspend_ordering,
168 .ident = "Asus Pundit P1-AH2 (M2N8L motherboard)",
170 DMI_MATCH(DMI_BOARD_VENDOR, "ASUSTek Computer INC."),
171 DMI_MATCH(DMI_BOARD_NAME, "M2N8L"),
175 .callback = init_old_suspend_ordering,
176 .ident = "Panasonic CF51-2L",
178 DMI_MATCH(DMI_BOARD_VENDOR,
179 "Matsushita Electric Industrial Co.,Ltd."),
180 DMI_MATCH(DMI_BOARD_NAME, "CF51-2L"),
184 .callback = init_nvs_nosave,
185 .ident = "Sony Vaio VGN-FW41E_H",
187 DMI_MATCH(DMI_SYS_VENDOR, "Sony Corporation"),
188 DMI_MATCH(DMI_PRODUCT_NAME, "VGN-FW41E_H"),
192 .callback = init_nvs_nosave,
193 .ident = "Sony Vaio VGN-FW21E",
195 DMI_MATCH(DMI_SYS_VENDOR, "Sony Corporation"),
196 DMI_MATCH(DMI_PRODUCT_NAME, "VGN-FW21E"),
200 .callback = init_nvs_nosave,
201 .ident = "Sony Vaio VGN-FW21M",
203 DMI_MATCH(DMI_SYS_VENDOR, "Sony Corporation"),
204 DMI_MATCH(DMI_PRODUCT_NAME, "VGN-FW21M"),
208 .callback = init_nvs_nosave,
209 .ident = "Sony Vaio VPCEB17FX",
211 DMI_MATCH(DMI_SYS_VENDOR, "Sony Corporation"),
212 DMI_MATCH(DMI_PRODUCT_NAME, "VPCEB17FX"),
216 .callback = init_nvs_nosave,
217 .ident = "Sony Vaio VGN-SR11M",
219 DMI_MATCH(DMI_SYS_VENDOR, "Sony Corporation"),
220 DMI_MATCH(DMI_PRODUCT_NAME, "VGN-SR11M"),
224 .callback = init_nvs_nosave,
225 .ident = "Everex StepNote Series",
227 DMI_MATCH(DMI_SYS_VENDOR, "Everex Systems, Inc."),
228 DMI_MATCH(DMI_PRODUCT_NAME, "Everex StepNote Series"),
232 .callback = init_nvs_nosave,
233 .ident = "Sony Vaio VPCEB1Z1E",
235 DMI_MATCH(DMI_SYS_VENDOR, "Sony Corporation"),
236 DMI_MATCH(DMI_PRODUCT_NAME, "VPCEB1Z1E"),
240 .callback = init_nvs_nosave,
241 .ident = "Sony Vaio VGN-NW130D",
243 DMI_MATCH(DMI_SYS_VENDOR, "Sony Corporation"),
244 DMI_MATCH(DMI_PRODUCT_NAME, "VGN-NW130D"),
248 .callback = init_nvs_nosave,
249 .ident = "Sony Vaio VPCCW29FX",
251 DMI_MATCH(DMI_SYS_VENDOR, "Sony Corporation"),
252 DMI_MATCH(DMI_PRODUCT_NAME, "VPCCW29FX"),
256 .callback = init_nvs_nosave,
257 .ident = "Averatec AV1020-ED2",
259 DMI_MATCH(DMI_SYS_VENDOR, "AVERATEC"),
260 DMI_MATCH(DMI_PRODUCT_NAME, "1000 Series"),
264 .callback = init_old_suspend_ordering,
265 .ident = "Asus A8N-SLI DELUXE",
267 DMI_MATCH(DMI_BOARD_VENDOR, "ASUSTeK Computer INC."),
268 DMI_MATCH(DMI_BOARD_NAME, "A8N-SLI DELUXE"),
272 .callback = init_old_suspend_ordering,
273 .ident = "Asus A8N-SLI Premium",
275 DMI_MATCH(DMI_BOARD_VENDOR, "ASUSTeK Computer INC."),
276 DMI_MATCH(DMI_BOARD_NAME, "A8N-SLI Premium"),
280 .callback = init_nvs_nosave,
281 .ident = "Sony Vaio VGN-SR26GN_P",
283 DMI_MATCH(DMI_SYS_VENDOR, "Sony Corporation"),
284 DMI_MATCH(DMI_PRODUCT_NAME, "VGN-SR26GN_P"),
288 .callback = init_nvs_nosave,
289 .ident = "Sony Vaio VPCEB1S1E",
291 DMI_MATCH(DMI_SYS_VENDOR, "Sony Corporation"),
292 DMI_MATCH(DMI_PRODUCT_NAME, "VPCEB1S1E"),
296 .callback = init_nvs_nosave,
297 .ident = "Sony Vaio VGN-FW520F",
299 DMI_MATCH(DMI_SYS_VENDOR, "Sony Corporation"),
300 DMI_MATCH(DMI_PRODUCT_NAME, "VGN-FW520F"),
304 .callback = init_nvs_nosave,
305 .ident = "Asus K54C",
307 DMI_MATCH(DMI_SYS_VENDOR, "ASUSTeK Computer Inc."),
308 DMI_MATCH(DMI_PRODUCT_NAME, "K54C"),
312 .callback = init_nvs_nosave,
313 .ident = "Asus K54HR",
315 DMI_MATCH(DMI_SYS_VENDOR, "ASUSTeK Computer Inc."),
316 DMI_MATCH(DMI_PRODUCT_NAME, "K54HR"),
322 static void acpi_sleep_dmi_check(void)
324 dmi_check_system(acpisleep_dmi_table);
328 * acpi_pm_freeze - Disable the GPEs and suspend EC transactions.
330 static int acpi_pm_freeze(void)
332 acpi_disable_all_gpes();
333 acpi_os_wait_events_complete();
334 acpi_ec_block_transactions();
339 * acpi_pre_suspend - Enable wakeup devices, "freeze" EC and save NVS.
341 static int acpi_pm_pre_suspend(void)
344 return suspend_nvs_save();
348 * __acpi_pm_prepare - Prepare the platform to enter the target state.
350 * If necessary, set the firmware waking vector and do arch-specific
351 * nastiness to get the wakeup code to the waking vector.
353 static int __acpi_pm_prepare(void)
355 int error = acpi_sleep_prepare(acpi_target_sleep_state);
357 acpi_target_sleep_state = ACPI_STATE_S0;
363 * acpi_pm_prepare - Prepare the platform to enter the target sleep
364 * state and disable the GPEs.
366 static int acpi_pm_prepare(void)
368 int error = __acpi_pm_prepare();
370 error = acpi_pm_pre_suspend();
375 static int find_powerf_dev(struct device *dev, void *data)
377 struct acpi_device *device = to_acpi_device(dev);
378 const char *hid = acpi_device_hid(device);
380 return !strcmp(hid, ACPI_BUTTON_HID_POWERF);
384 * acpi_pm_finish - Instruct the platform to leave a sleep state.
386 * This is called after we wake back up (or if entering the sleep state
389 static void acpi_pm_finish(void)
391 struct device *pwr_btn_dev;
392 u32 acpi_state = acpi_target_sleep_state;
394 acpi_ec_unblock_transactions();
397 if (acpi_state == ACPI_STATE_S0)
400 printk(KERN_INFO PREFIX "Waking up from system sleep state S%d\n",
402 acpi_disable_wakeup_devices(acpi_state);
403 acpi_leave_sleep_state(acpi_state);
405 /* reset firmware waking vector */
406 acpi_set_firmware_waking_vector((acpi_physical_address) 0);
408 acpi_target_sleep_state = ACPI_STATE_S0;
410 acpi_resume_power_resources();
412 /* If we were woken with the fixed power button, provide a small
413 * hint to userspace in the form of a wakeup event on the fixed power
414 * button device (if it can be found).
416 * We delay the event generation til now, as the PM layer requires
417 * timekeeping to be running before we generate events. */
418 if (!pwr_btn_event_pending)
421 pwr_btn_event_pending = false;
422 pwr_btn_dev = bus_find_device(&acpi_bus_type, NULL, NULL,
425 pm_wakeup_event(pwr_btn_dev, 0);
426 put_device(pwr_btn_dev);
431 * acpi_pm_start - Start system PM transition.
433 static void acpi_pm_start(u32 acpi_state)
435 acpi_target_sleep_state = acpi_state;
436 acpi_sleep_tts_switch(acpi_target_sleep_state);
437 acpi_scan_lock_acquire();
441 * acpi_pm_end - Finish up system PM transition.
443 static void acpi_pm_end(void)
445 acpi_scan_lock_release();
447 * This is necessary in case acpi_pm_finish() is not called during a
448 * failing transition to a sleep state.
450 acpi_target_sleep_state = ACPI_STATE_S0;
451 acpi_sleep_tts_switch(acpi_target_sleep_state);
453 #else /* !CONFIG_ACPI_SLEEP */
454 #define acpi_target_sleep_state ACPI_STATE_S0
455 static inline void acpi_sleep_dmi_check(void) {}
456 #endif /* CONFIG_ACPI_SLEEP */
458 #ifdef CONFIG_SUSPEND
459 static u32 acpi_suspend_states[] = {
460 [PM_SUSPEND_ON] = ACPI_STATE_S0,
461 [PM_SUSPEND_STANDBY] = ACPI_STATE_S1,
462 [PM_SUSPEND_MEM] = ACPI_STATE_S3,
463 [PM_SUSPEND_MAX] = ACPI_STATE_S5
467 * acpi_suspend_begin - Set the target system sleep state to the state
468 * associated with given @pm_state, if supported.
470 static int acpi_suspend_begin(suspend_state_t pm_state)
472 u32 acpi_state = acpi_suspend_states[pm_state];
475 error = (nvs_nosave || nvs_nosave_s3) ? 0 : suspend_nvs_alloc();
479 if (!sleep_states[acpi_state]) {
480 pr_err("ACPI does not support sleep state S%u\n", acpi_state);
484 acpi_pm_start(acpi_state);
489 * acpi_suspend_enter - Actually enter a sleep state.
492 * Flush caches and go to sleep. For STR we have to call arch-specific
493 * assembly, which in turn call acpi_enter_sleep_state().
494 * It's unfortunate, but it works. Please fix if you're feeling frisky.
496 static int acpi_suspend_enter(suspend_state_t pm_state)
498 acpi_status status = AE_OK;
499 u32 acpi_state = acpi_target_sleep_state;
502 ACPI_FLUSH_CPU_CACHE();
504 switch (acpi_state) {
507 status = acpi_enter_sleep_state(acpi_state);
511 if (!acpi_suspend_lowlevel)
513 error = acpi_suspend_lowlevel();
516 pr_info(PREFIX "Low-level resume complete\n");
520 /* This violates the spec but is required for bug compatibility. */
521 acpi_write_bit_register(ACPI_BITREG_SCI_ENABLE, 1);
523 /* Reprogram control registers */
524 acpi_leave_sleep_state_prep(acpi_state);
526 /* ACPI 3.0 specs (P62) says that it's the responsibility
527 * of the OSPM to clear the status bit [ implying that the
528 * POWER_BUTTON event should not reach userspace ]
530 * However, we do generate a small hint for userspace in the form of
531 * a wakeup event. We flag this condition for now and generate the
532 * event later, as we're currently too early in resume to be able to
533 * generate wakeup events.
535 if (ACPI_SUCCESS(status) && (acpi_state == ACPI_STATE_S3)) {
536 acpi_event_status pwr_btn_status = ACPI_EVENT_FLAG_DISABLED;
538 acpi_get_event_status(ACPI_EVENT_POWER_BUTTON, &pwr_btn_status);
540 if (pwr_btn_status & ACPI_EVENT_FLAG_SET) {
541 acpi_clear_event(ACPI_EVENT_POWER_BUTTON);
543 pwr_btn_event_pending = true;
548 * Disable and clear GPE status before interrupt is enabled. Some GPEs
549 * (like wakeup GPE) haven't handler, this can avoid such GPE misfire.
550 * acpi_leave_sleep_state will reenable specific GPEs later
552 acpi_disable_all_gpes();
553 /* Allow EC transactions to happen. */
554 acpi_ec_unblock_transactions_early();
556 suspend_nvs_restore();
558 return ACPI_SUCCESS(status) ? 0 : -EFAULT;
561 static int acpi_suspend_state_valid(suspend_state_t pm_state)
567 case PM_SUSPEND_STANDBY:
569 acpi_state = acpi_suspend_states[pm_state];
571 return sleep_states[acpi_state];
577 static const struct platform_suspend_ops acpi_suspend_ops = {
578 .valid = acpi_suspend_state_valid,
579 .begin = acpi_suspend_begin,
580 .prepare_late = acpi_pm_prepare,
581 .enter = acpi_suspend_enter,
582 .wake = acpi_pm_finish,
587 * acpi_suspend_begin_old - Set the target system sleep state to the
588 * state associated with given @pm_state, if supported, and
589 * execute the _PTS control method. This function is used if the
590 * pre-ACPI 2.0 suspend ordering has been requested.
592 static int acpi_suspend_begin_old(suspend_state_t pm_state)
594 int error = acpi_suspend_begin(pm_state);
596 error = __acpi_pm_prepare();
602 * The following callbacks are used if the pre-ACPI 2.0 suspend ordering has
605 static const struct platform_suspend_ops acpi_suspend_ops_old = {
606 .valid = acpi_suspend_state_valid,
607 .begin = acpi_suspend_begin_old,
608 .prepare_late = acpi_pm_pre_suspend,
609 .enter = acpi_suspend_enter,
610 .wake = acpi_pm_finish,
612 .recover = acpi_pm_finish,
615 static int acpi_freeze_begin(void)
617 acpi_scan_lock_acquire();
621 static void acpi_freeze_end(void)
623 acpi_scan_lock_release();
626 static const struct platform_freeze_ops acpi_freeze_ops = {
627 .begin = acpi_freeze_begin,
628 .end = acpi_freeze_end,
631 static void acpi_sleep_suspend_setup(void)
635 for (i = ACPI_STATE_S1; i < ACPI_STATE_S4; i++)
636 if (acpi_sleep_state_supported(i))
639 suspend_set_ops(old_suspend_ordering ?
640 &acpi_suspend_ops_old : &acpi_suspend_ops);
641 freeze_set_ops(&acpi_freeze_ops);
644 #else /* !CONFIG_SUSPEND */
645 static inline void acpi_sleep_suspend_setup(void) {}
646 #endif /* !CONFIG_SUSPEND */
648 #ifdef CONFIG_HIBERNATION
649 static unsigned long s4_hardware_signature;
650 static struct acpi_table_facs *facs;
651 static bool nosigcheck;
653 void __init acpi_no_s4_hw_signature(void)
658 static int acpi_hibernation_begin(void)
662 error = nvs_nosave ? 0 : suspend_nvs_alloc();
664 acpi_pm_start(ACPI_STATE_S4);
669 static int acpi_hibernation_enter(void)
671 acpi_status status = AE_OK;
673 ACPI_FLUSH_CPU_CACHE();
675 /* This shouldn't return. If it returns, we have a problem */
676 status = acpi_enter_sleep_state(ACPI_STATE_S4);
677 /* Reprogram control registers */
678 acpi_leave_sleep_state_prep(ACPI_STATE_S4);
680 return ACPI_SUCCESS(status) ? 0 : -EFAULT;
683 static void acpi_hibernation_leave(void)
686 * If ACPI is not enabled by the BIOS and the boot kernel, we need to
690 /* Reprogram control registers */
691 acpi_leave_sleep_state_prep(ACPI_STATE_S4);
692 /* Check the hardware signature */
693 if (facs && s4_hardware_signature != facs->hardware_signature)
694 pr_crit("ACPI: Hardware changed while hibernated, success doubtful!\n");
695 /* Restore the NVS memory area */
696 suspend_nvs_restore();
697 /* Allow EC transactions to happen. */
698 acpi_ec_unblock_transactions_early();
701 static void acpi_pm_thaw(void)
703 acpi_ec_unblock_transactions();
704 acpi_enable_all_runtime_gpes();
707 static const struct platform_hibernation_ops acpi_hibernation_ops = {
708 .begin = acpi_hibernation_begin,
710 .pre_snapshot = acpi_pm_prepare,
711 .finish = acpi_pm_finish,
712 .prepare = acpi_pm_prepare,
713 .enter = acpi_hibernation_enter,
714 .leave = acpi_hibernation_leave,
715 .pre_restore = acpi_pm_freeze,
716 .restore_cleanup = acpi_pm_thaw,
720 * acpi_hibernation_begin_old - Set the target system sleep state to
721 * ACPI_STATE_S4 and execute the _PTS control method. This
722 * function is used if the pre-ACPI 2.0 suspend ordering has been
725 static int acpi_hibernation_begin_old(void)
729 * The _TTS object should always be evaluated before the _PTS object.
730 * When the old_suspended_ordering is true, the _PTS object is
731 * evaluated in the acpi_sleep_prepare.
733 acpi_sleep_tts_switch(ACPI_STATE_S4);
735 error = acpi_sleep_prepare(ACPI_STATE_S4);
739 error = suspend_nvs_alloc();
741 acpi_target_sleep_state = ACPI_STATE_S4;
742 acpi_scan_lock_acquire();
749 * The following callbacks are used if the pre-ACPI 2.0 suspend ordering has
752 static const struct platform_hibernation_ops acpi_hibernation_ops_old = {
753 .begin = acpi_hibernation_begin_old,
755 .pre_snapshot = acpi_pm_pre_suspend,
756 .prepare = acpi_pm_freeze,
757 .finish = acpi_pm_finish,
758 .enter = acpi_hibernation_enter,
759 .leave = acpi_hibernation_leave,
760 .pre_restore = acpi_pm_freeze,
761 .restore_cleanup = acpi_pm_thaw,
762 .recover = acpi_pm_finish,
765 static void acpi_sleep_hibernate_setup(void)
767 if (!acpi_sleep_state_supported(ACPI_STATE_S4))
770 hibernation_set_ops(old_suspend_ordering ?
771 &acpi_hibernation_ops_old : &acpi_hibernation_ops);
772 sleep_states[ACPI_STATE_S4] = 1;
776 acpi_get_table(ACPI_SIG_FACS, 1, (struct acpi_table_header **)&facs);
778 s4_hardware_signature = facs->hardware_signature;
780 #else /* !CONFIG_HIBERNATION */
781 static inline void acpi_sleep_hibernate_setup(void) {}
782 #endif /* !CONFIG_HIBERNATION */
784 int acpi_suspend(u32 acpi_state)
786 suspend_state_t states[] = {
787 [1] = PM_SUSPEND_STANDBY,
788 [3] = PM_SUSPEND_MEM,
792 if (acpi_state < 6 && states[acpi_state])
793 return pm_suspend(states[acpi_state]);
799 static void acpi_power_off_prepare(void)
801 /* Prepare to power off the system */
802 acpi_sleep_prepare(ACPI_STATE_S5);
803 acpi_disable_all_gpes();
806 static void acpi_power_off(void)
808 /* acpi_sleep_prepare(ACPI_STATE_S5) should have already been called */
809 printk(KERN_DEBUG "%s called\n", __func__);
811 acpi_enter_sleep_state(ACPI_STATE_S5);
814 int __init acpi_sleep_init(void)
816 char supported[ACPI_S_STATE_COUNT * 3 + 1];
817 char *pos = supported;
820 acpi_sleep_dmi_check();
822 sleep_states[ACPI_STATE_S0] = 1;
824 acpi_sleep_suspend_setup();
825 acpi_sleep_hibernate_setup();
827 if (acpi_sleep_state_supported(ACPI_STATE_S5)) {
828 sleep_states[ACPI_STATE_S5] = 1;
829 pm_power_off_prepare = acpi_power_off_prepare;
830 pm_power_off = acpi_power_off;
834 for (i = 0; i < ACPI_S_STATE_COUNT; i++) {
836 pos += sprintf(pos, " S%d", i);
838 pr_info(PREFIX "(supports%s)\n", supported);
841 * Register the tts_notifier to reboot notifier list so that the _TTS
842 * object can also be evaluated when the system enters S5.
844 register_reboot_notifier(&tts_notifier);