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>
24 #include <acpi/acpi_bus.h>
25 #include <acpi/acpi_drivers.h>
30 static u8 sleep_states
[ACPI_S_STATE_COUNT
];
32 static void acpi_sleep_tts_switch(u32 acpi_state
)
34 union acpi_object in_arg
= { ACPI_TYPE_INTEGER
};
35 struct acpi_object_list arg_list
= { 1, &in_arg
};
36 acpi_status status
= AE_OK
;
38 in_arg
.integer
.value
= acpi_state
;
39 status
= acpi_evaluate_object(NULL
, "\\_TTS", &arg_list
, NULL
);
40 if (ACPI_FAILURE(status
) && status
!= AE_NOT_FOUND
) {
42 * OS can't evaluate the _TTS object correctly. Some warning
43 * message will be printed. But it won't break anything.
45 printk(KERN_NOTICE
"Failure in evaluating _TTS object\n");
49 static int tts_notify_reboot(struct notifier_block
*this,
50 unsigned long code
, void *x
)
52 acpi_sleep_tts_switch(ACPI_STATE_S5
);
56 static struct notifier_block tts_notifier
= {
57 .notifier_call
= tts_notify_reboot
,
62 static int acpi_sleep_prepare(u32 acpi_state
)
64 #ifdef CONFIG_ACPI_SLEEP
65 /* do we have a wakeup address for S2 and S3? */
66 if (acpi_state
== ACPI_STATE_S3
) {
67 if (!acpi_wakeup_address
)
69 acpi_set_firmware_waking_vector(acpi_wakeup_address
);
72 ACPI_FLUSH_CPU_CACHE();
74 printk(KERN_INFO PREFIX
"Preparing to enter system sleep state S%d\n",
76 acpi_enable_wakeup_devices(acpi_state
);
77 acpi_enter_sleep_state_prep(acpi_state
);
81 #ifdef CONFIG_ACPI_SLEEP
82 static u32 acpi_target_sleep_state
= ACPI_STATE_S0
;
84 u32
acpi_target_system_state(void)
86 return acpi_target_sleep_state
;
89 static bool pwr_btn_event_pending
;
92 * The ACPI specification wants us to save NVS memory regions during hibernation
93 * and to restore them during the subsequent resume. Windows does that also for
94 * suspend to RAM. However, it is known that this mechanism does not work on
95 * all machines, so we allow the user to disable it with the help of the
96 * 'acpi_sleep=nonvs' kernel command line option.
98 static bool nvs_nosave
;
100 void __init
acpi_nvs_nosave(void)
106 * The ACPI specification wants us to save NVS memory regions during hibernation
107 * but says nothing about saving NVS during S3. Not all versions of Windows
108 * save NVS on S3 suspend either, and it is clear that not all systems need
109 * NVS to be saved at S3 time. To improve suspend/resume time, allow the
110 * user to disable saving NVS on S3 if their system does not require it, but
111 * continue to save/restore NVS for S4 as specified.
113 static bool nvs_nosave_s3
;
115 void __init
acpi_nvs_nosave_s3(void)
117 nvs_nosave_s3
= true;
121 * ACPI 1.0 wants us to execute _PTS before suspending devices, so we allow the
122 * user to request that behavior by using the 'acpi_old_suspend_ordering'
123 * kernel command line option that causes the following variable to be set.
125 static bool old_suspend_ordering
;
127 void __init
acpi_old_suspend_ordering(void)
129 old_suspend_ordering
= true;
132 static int __init
init_old_suspend_ordering(const struct dmi_system_id
*d
)
134 acpi_old_suspend_ordering();
138 static int __init
init_nvs_nosave(const struct dmi_system_id
*d
)
144 static struct dmi_system_id __initdata acpisleep_dmi_table
[] = {
146 .callback
= init_old_suspend_ordering
,
147 .ident
= "Abit KN9 (nForce4 variant)",
149 DMI_MATCH(DMI_BOARD_VENDOR
, "http://www.abit.com.tw/"),
150 DMI_MATCH(DMI_BOARD_NAME
, "KN9 Series(NF-CK804)"),
154 .callback
= init_old_suspend_ordering
,
155 .ident
= "HP xw4600 Workstation",
157 DMI_MATCH(DMI_SYS_VENDOR
, "Hewlett-Packard"),
158 DMI_MATCH(DMI_PRODUCT_NAME
, "HP xw4600 Workstation"),
162 .callback
= init_old_suspend_ordering
,
163 .ident
= "Asus Pundit P1-AH2 (M2N8L motherboard)",
165 DMI_MATCH(DMI_BOARD_VENDOR
, "ASUSTek Computer INC."),
166 DMI_MATCH(DMI_BOARD_NAME
, "M2N8L"),
170 .callback
= init_old_suspend_ordering
,
171 .ident
= "Panasonic CF51-2L",
173 DMI_MATCH(DMI_BOARD_VENDOR
,
174 "Matsushita Electric Industrial Co.,Ltd."),
175 DMI_MATCH(DMI_BOARD_NAME
, "CF51-2L"),
179 .callback
= init_nvs_nosave
,
180 .ident
= "Sony Vaio VGN-FW41E_H",
182 DMI_MATCH(DMI_SYS_VENDOR
, "Sony Corporation"),
183 DMI_MATCH(DMI_PRODUCT_NAME
, "VGN-FW41E_H"),
187 .callback
= init_nvs_nosave
,
188 .ident
= "Sony Vaio VGN-FW21E",
190 DMI_MATCH(DMI_SYS_VENDOR
, "Sony Corporation"),
191 DMI_MATCH(DMI_PRODUCT_NAME
, "VGN-FW21E"),
195 .callback
= init_nvs_nosave
,
196 .ident
= "Sony Vaio VPCEB17FX",
198 DMI_MATCH(DMI_SYS_VENDOR
, "Sony Corporation"),
199 DMI_MATCH(DMI_PRODUCT_NAME
, "VPCEB17FX"),
203 .callback
= init_nvs_nosave
,
204 .ident
= "Sony Vaio VGN-SR11M",
206 DMI_MATCH(DMI_SYS_VENDOR
, "Sony Corporation"),
207 DMI_MATCH(DMI_PRODUCT_NAME
, "VGN-SR11M"),
211 .callback
= init_nvs_nosave
,
212 .ident
= "Everex StepNote Series",
214 DMI_MATCH(DMI_SYS_VENDOR
, "Everex Systems, Inc."),
215 DMI_MATCH(DMI_PRODUCT_NAME
, "Everex StepNote Series"),
219 .callback
= init_nvs_nosave
,
220 .ident
= "Sony Vaio VPCEB1Z1E",
222 DMI_MATCH(DMI_SYS_VENDOR
, "Sony Corporation"),
223 DMI_MATCH(DMI_PRODUCT_NAME
, "VPCEB1Z1E"),
227 .callback
= init_nvs_nosave
,
228 .ident
= "Sony Vaio VGN-NW130D",
230 DMI_MATCH(DMI_SYS_VENDOR
, "Sony Corporation"),
231 DMI_MATCH(DMI_PRODUCT_NAME
, "VGN-NW130D"),
235 .callback
= init_nvs_nosave
,
236 .ident
= "Sony Vaio VPCCW29FX",
238 DMI_MATCH(DMI_SYS_VENDOR
, "Sony Corporation"),
239 DMI_MATCH(DMI_PRODUCT_NAME
, "VPCCW29FX"),
243 .callback
= init_nvs_nosave
,
244 .ident
= "Averatec AV1020-ED2",
246 DMI_MATCH(DMI_SYS_VENDOR
, "AVERATEC"),
247 DMI_MATCH(DMI_PRODUCT_NAME
, "1000 Series"),
251 .callback
= init_old_suspend_ordering
,
252 .ident
= "Asus A8N-SLI DELUXE",
254 DMI_MATCH(DMI_BOARD_VENDOR
, "ASUSTeK Computer INC."),
255 DMI_MATCH(DMI_BOARD_NAME
, "A8N-SLI DELUXE"),
259 .callback
= init_old_suspend_ordering
,
260 .ident
= "Asus A8N-SLI Premium",
262 DMI_MATCH(DMI_BOARD_VENDOR
, "ASUSTeK Computer INC."),
263 DMI_MATCH(DMI_BOARD_NAME
, "A8N-SLI Premium"),
267 .callback
= init_nvs_nosave
,
268 .ident
= "Sony Vaio VGN-SR26GN_P",
270 DMI_MATCH(DMI_SYS_VENDOR
, "Sony Corporation"),
271 DMI_MATCH(DMI_PRODUCT_NAME
, "VGN-SR26GN_P"),
275 .callback
= init_nvs_nosave
,
276 .ident
= "Sony Vaio VPCEB1S1E",
278 DMI_MATCH(DMI_SYS_VENDOR
, "Sony Corporation"),
279 DMI_MATCH(DMI_PRODUCT_NAME
, "VPCEB1S1E"),
283 .callback
= init_nvs_nosave
,
284 .ident
= "Sony Vaio VGN-FW520F",
286 DMI_MATCH(DMI_SYS_VENDOR
, "Sony Corporation"),
287 DMI_MATCH(DMI_PRODUCT_NAME
, "VGN-FW520F"),
291 .callback
= init_nvs_nosave
,
292 .ident
= "Asus K54C",
294 DMI_MATCH(DMI_SYS_VENDOR
, "ASUSTeK Computer Inc."),
295 DMI_MATCH(DMI_PRODUCT_NAME
, "K54C"),
299 .callback
= init_nvs_nosave
,
300 .ident
= "Asus K54HR",
302 DMI_MATCH(DMI_SYS_VENDOR
, "ASUSTeK Computer Inc."),
303 DMI_MATCH(DMI_PRODUCT_NAME
, "K54HR"),
309 static void acpi_sleep_dmi_check(void)
311 dmi_check_system(acpisleep_dmi_table
);
315 * acpi_pm_freeze - Disable the GPEs and suspend EC transactions.
317 static int acpi_pm_freeze(void)
319 acpi_disable_all_gpes();
320 acpi_os_wait_events_complete();
321 acpi_ec_block_transactions();
326 * acpi_pre_suspend - Enable wakeup devices, "freeze" EC and save NVS.
328 static int acpi_pm_pre_suspend(void)
331 return suspend_nvs_save();
335 * __acpi_pm_prepare - Prepare the platform to enter the target state.
337 * If necessary, set the firmware waking vector and do arch-specific
338 * nastiness to get the wakeup code to the waking vector.
340 static int __acpi_pm_prepare(void)
342 int error
= acpi_sleep_prepare(acpi_target_sleep_state
);
344 acpi_target_sleep_state
= ACPI_STATE_S0
;
350 * acpi_pm_prepare - Prepare the platform to enter the target sleep
351 * state and disable the GPEs.
353 static int acpi_pm_prepare(void)
355 int error
= __acpi_pm_prepare();
357 error
= acpi_pm_pre_suspend();
362 static int find_powerf_dev(struct device
*dev
, void *data
)
364 struct acpi_device
*device
= to_acpi_device(dev
);
365 const char *hid
= acpi_device_hid(device
);
367 return !strcmp(hid
, ACPI_BUTTON_HID_POWERF
);
371 * acpi_pm_finish - Instruct the platform to leave a sleep state.
373 * This is called after we wake back up (or if entering the sleep state
376 static void acpi_pm_finish(void)
378 struct device
*pwr_btn_dev
;
379 u32 acpi_state
= acpi_target_sleep_state
;
381 acpi_ec_unblock_transactions();
384 if (acpi_state
== ACPI_STATE_S0
)
387 printk(KERN_INFO PREFIX
"Waking up from system sleep state S%d\n",
389 acpi_disable_wakeup_devices(acpi_state
);
390 acpi_leave_sleep_state(acpi_state
);
392 /* reset firmware waking vector */
393 acpi_set_firmware_waking_vector((acpi_physical_address
) 0);
395 acpi_target_sleep_state
= ACPI_STATE_S0
;
397 acpi_resume_power_resources();
399 /* If we were woken with the fixed power button, provide a small
400 * hint to userspace in the form of a wakeup event on the fixed power
401 * button device (if it can be found).
403 * We delay the event generation til now, as the PM layer requires
404 * timekeeping to be running before we generate events. */
405 if (!pwr_btn_event_pending
)
408 pwr_btn_event_pending
= false;
409 pwr_btn_dev
= bus_find_device(&acpi_bus_type
, NULL
, NULL
,
412 pm_wakeup_event(pwr_btn_dev
, 0);
413 put_device(pwr_btn_dev
);
418 * acpi_pm_end - Finish up suspend sequence.
420 static void acpi_pm_end(void)
423 * This is necessary in case acpi_pm_finish() is not called during a
424 * failing transition to a sleep state.
426 acpi_target_sleep_state
= ACPI_STATE_S0
;
427 acpi_sleep_tts_switch(acpi_target_sleep_state
);
429 #else /* !CONFIG_ACPI_SLEEP */
430 #define acpi_target_sleep_state ACPI_STATE_S0
431 static inline void acpi_sleep_dmi_check(void) {}
432 #endif /* CONFIG_ACPI_SLEEP */
434 #ifdef CONFIG_SUSPEND
435 static u32 acpi_suspend_states
[] = {
436 [PM_SUSPEND_ON
] = ACPI_STATE_S0
,
437 [PM_SUSPEND_STANDBY
] = ACPI_STATE_S1
,
438 [PM_SUSPEND_MEM
] = ACPI_STATE_S3
,
439 [PM_SUSPEND_MAX
] = ACPI_STATE_S5
443 * acpi_suspend_begin - Set the target system sleep state to the state
444 * associated with given @pm_state, if supported.
446 static int acpi_suspend_begin(suspend_state_t pm_state
)
448 u32 acpi_state
= acpi_suspend_states
[pm_state
];
451 error
= (nvs_nosave
|| nvs_nosave_s3
) ? 0 : suspend_nvs_alloc();
455 if (sleep_states
[acpi_state
]) {
456 acpi_target_sleep_state
= acpi_state
;
457 acpi_sleep_tts_switch(acpi_target_sleep_state
);
459 printk(KERN_ERR
"ACPI does not support this state: %d\n",
467 * acpi_suspend_enter - Actually enter a sleep state.
470 * Flush caches and go to sleep. For STR we have to call arch-specific
471 * assembly, which in turn call acpi_enter_sleep_state().
472 * It's unfortunate, but it works. Please fix if you're feeling frisky.
474 static int acpi_suspend_enter(suspend_state_t pm_state
)
476 acpi_status status
= AE_OK
;
477 u32 acpi_state
= acpi_target_sleep_state
;
480 ACPI_FLUSH_CPU_CACHE();
482 switch (acpi_state
) {
485 status
= acpi_enter_sleep_state(acpi_state
);
489 error
= acpi_suspend_lowlevel();
492 pr_info(PREFIX
"Low-level resume complete\n");
496 /* This violates the spec but is required for bug compatibility. */
497 acpi_write_bit_register(ACPI_BITREG_SCI_ENABLE
, 1);
499 /* Reprogram control registers */
500 acpi_leave_sleep_state_prep(acpi_state
);
502 /* ACPI 3.0 specs (P62) says that it's the responsibility
503 * of the OSPM to clear the status bit [ implying that the
504 * POWER_BUTTON event should not reach userspace ]
506 * However, we do generate a small hint for userspace in the form of
507 * a wakeup event. We flag this condition for now and generate the
508 * event later, as we're currently too early in resume to be able to
509 * generate wakeup events.
511 if (ACPI_SUCCESS(status
) && (acpi_state
== ACPI_STATE_S3
)) {
512 acpi_event_status pwr_btn_status
;
514 acpi_get_event_status(ACPI_EVENT_POWER_BUTTON
, &pwr_btn_status
);
516 if (pwr_btn_status
& ACPI_EVENT_FLAG_SET
) {
517 acpi_clear_event(ACPI_EVENT_POWER_BUTTON
);
519 pwr_btn_event_pending
= true;
524 * Disable and clear GPE status before interrupt is enabled. Some GPEs
525 * (like wakeup GPE) haven't handler, this can avoid such GPE misfire.
526 * acpi_leave_sleep_state will reenable specific GPEs later
528 acpi_disable_all_gpes();
529 /* Allow EC transactions to happen. */
530 acpi_ec_unblock_transactions_early();
532 suspend_nvs_restore();
534 return ACPI_SUCCESS(status
) ? 0 : -EFAULT
;
537 static int acpi_suspend_state_valid(suspend_state_t pm_state
)
543 case PM_SUSPEND_STANDBY
:
545 acpi_state
= acpi_suspend_states
[pm_state
];
547 return sleep_states
[acpi_state
];
553 static const struct platform_suspend_ops acpi_suspend_ops
= {
554 .valid
= acpi_suspend_state_valid
,
555 .begin
= acpi_suspend_begin
,
556 .prepare_late
= acpi_pm_prepare
,
557 .enter
= acpi_suspend_enter
,
558 .wake
= acpi_pm_finish
,
563 * acpi_suspend_begin_old - Set the target system sleep state to the
564 * state associated with given @pm_state, if supported, and
565 * execute the _PTS control method. This function is used if the
566 * pre-ACPI 2.0 suspend ordering has been requested.
568 static int acpi_suspend_begin_old(suspend_state_t pm_state
)
570 int error
= acpi_suspend_begin(pm_state
);
572 error
= __acpi_pm_prepare();
578 * The following callbacks are used if the pre-ACPI 2.0 suspend ordering has
581 static const struct platform_suspend_ops acpi_suspend_ops_old
= {
582 .valid
= acpi_suspend_state_valid
,
583 .begin
= acpi_suspend_begin_old
,
584 .prepare_late
= acpi_pm_pre_suspend
,
585 .enter
= acpi_suspend_enter
,
586 .wake
= acpi_pm_finish
,
588 .recover
= acpi_pm_finish
,
591 static void acpi_sleep_suspend_setup(void)
595 for (i
= ACPI_STATE_S1
; i
< ACPI_STATE_S4
; i
++) {
599 status
= acpi_get_sleep_type_data(i
, &type_a
, &type_b
);
600 if (ACPI_SUCCESS(status
)) {
606 suspend_set_ops(old_suspend_ordering
?
607 &acpi_suspend_ops_old
: &acpi_suspend_ops
);
609 #else /* !CONFIG_SUSPEND */
610 static inline void acpi_sleep_suspend_setup(void) {}
611 #endif /* !CONFIG_SUSPEND */
613 #ifdef CONFIG_HIBERNATION
614 static unsigned long s4_hardware_signature
;
615 static struct acpi_table_facs
*facs
;
616 static bool nosigcheck
;
618 void __init
acpi_no_s4_hw_signature(void)
623 static int acpi_hibernation_begin(void)
627 error
= nvs_nosave
? 0 : suspend_nvs_alloc();
629 acpi_target_sleep_state
= ACPI_STATE_S4
;
630 acpi_sleep_tts_switch(acpi_target_sleep_state
);
636 static int acpi_hibernation_enter(void)
638 acpi_status status
= AE_OK
;
640 ACPI_FLUSH_CPU_CACHE();
642 /* This shouldn't return. If it returns, we have a problem */
643 status
= acpi_enter_sleep_state(ACPI_STATE_S4
);
644 /* Reprogram control registers */
645 acpi_leave_sleep_state_prep(ACPI_STATE_S4
);
647 return ACPI_SUCCESS(status
) ? 0 : -EFAULT
;
650 static void acpi_hibernation_leave(void)
653 * If ACPI is not enabled by the BIOS and the boot kernel, we need to
657 /* Reprogram control registers */
658 acpi_leave_sleep_state_prep(ACPI_STATE_S4
);
659 /* Check the hardware signature */
660 if (facs
&& s4_hardware_signature
!= facs
->hardware_signature
) {
661 printk(KERN_EMERG
"ACPI: Hardware changed while hibernated, "
663 panic("ACPI S4 hardware signature mismatch");
665 /* Restore the NVS memory area */
666 suspend_nvs_restore();
667 /* Allow EC transactions to happen. */
668 acpi_ec_unblock_transactions_early();
671 static void acpi_pm_thaw(void)
673 acpi_ec_unblock_transactions();
674 acpi_enable_all_runtime_gpes();
677 static const struct platform_hibernation_ops acpi_hibernation_ops
= {
678 .begin
= acpi_hibernation_begin
,
680 .pre_snapshot
= acpi_pm_prepare
,
681 .finish
= acpi_pm_finish
,
682 .prepare
= acpi_pm_prepare
,
683 .enter
= acpi_hibernation_enter
,
684 .leave
= acpi_hibernation_leave
,
685 .pre_restore
= acpi_pm_freeze
,
686 .restore_cleanup
= acpi_pm_thaw
,
690 * acpi_hibernation_begin_old - Set the target system sleep state to
691 * ACPI_STATE_S4 and execute the _PTS control method. This
692 * function is used if the pre-ACPI 2.0 suspend ordering has been
695 static int acpi_hibernation_begin_old(void)
699 * The _TTS object should always be evaluated before the _PTS object.
700 * When the old_suspended_ordering is true, the _PTS object is
701 * evaluated in the acpi_sleep_prepare.
703 acpi_sleep_tts_switch(ACPI_STATE_S4
);
705 error
= acpi_sleep_prepare(ACPI_STATE_S4
);
709 error
= suspend_nvs_alloc();
711 acpi_target_sleep_state
= ACPI_STATE_S4
;
717 * The following callbacks are used if the pre-ACPI 2.0 suspend ordering has
720 static const struct platform_hibernation_ops acpi_hibernation_ops_old
= {
721 .begin
= acpi_hibernation_begin_old
,
723 .pre_snapshot
= acpi_pm_pre_suspend
,
724 .prepare
= acpi_pm_freeze
,
725 .finish
= acpi_pm_finish
,
726 .enter
= acpi_hibernation_enter
,
727 .leave
= acpi_hibernation_leave
,
728 .pre_restore
= acpi_pm_freeze
,
729 .restore_cleanup
= acpi_pm_thaw
,
730 .recover
= acpi_pm_finish
,
733 static void acpi_sleep_hibernate_setup(void)
738 status
= acpi_get_sleep_type_data(ACPI_STATE_S4
, &type_a
, &type_b
);
739 if (ACPI_FAILURE(status
))
742 hibernation_set_ops(old_suspend_ordering
?
743 &acpi_hibernation_ops_old
: &acpi_hibernation_ops
);
744 sleep_states
[ACPI_STATE_S4
] = 1;
745 pr_cont(KERN_CONT
" S4");
749 acpi_get_table(ACPI_SIG_FACS
, 1, (struct acpi_table_header
**)&facs
);
751 s4_hardware_signature
= facs
->hardware_signature
;
753 #else /* !CONFIG_HIBERNATION */
754 static inline void acpi_sleep_hibernate_setup(void) {}
755 #endif /* !CONFIG_HIBERNATION */
757 int acpi_suspend(u32 acpi_state
)
759 suspend_state_t states
[] = {
760 [1] = PM_SUSPEND_STANDBY
,
761 [3] = PM_SUSPEND_MEM
,
765 if (acpi_state
< 6 && states
[acpi_state
])
766 return pm_suspend(states
[acpi_state
]);
772 static void acpi_power_off_prepare(void)
774 /* Prepare to power off the system */
775 acpi_sleep_prepare(ACPI_STATE_S5
);
776 acpi_disable_all_gpes();
779 static void acpi_power_off(void)
781 /* acpi_sleep_prepare(ACPI_STATE_S5) should have already been called */
782 printk(KERN_DEBUG
"%s called\n", __func__
);
784 acpi_enter_sleep_state(ACPI_STATE_S5
);
787 int __init
acpi_sleep_init(void)
795 acpi_sleep_dmi_check();
797 sleep_states
[ACPI_STATE_S0
] = 1;
798 pr_info(PREFIX
"(supports S0");
800 acpi_sleep_suspend_setup();
801 acpi_sleep_hibernate_setup();
803 status
= acpi_get_sleep_type_data(ACPI_STATE_S5
, &type_a
, &type_b
);
804 if (ACPI_SUCCESS(status
)) {
805 sleep_states
[ACPI_STATE_S5
] = 1;
807 pm_power_off_prepare
= acpi_power_off_prepare
;
808 pm_power_off
= acpi_power_off
;
812 * Register the tts_notifier to reboot notifier list so that the _TTS
813 * object can also be evaluated when the system enters S5.
815 register_reboot_notifier(&tts_notifier
);