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1 | Power Management Interface for System Sleep |
2 | ||
3 | Copyright (c) 2016 Intel Corp., Rafael J. Wysocki <rafael.j.wysocki@intel.com> | |
4 | ||
5 | The power management subsystem provides userspace with a unified sysfs interface | |
6 | for system sleep regardless of the underlying system architecture or platform. | |
7 | The interface is located in the /sys/power/ directory (assuming that sysfs is | |
8 | mounted at /sys). | |
9 | ||
10 | /sys/power/state is the system sleep state control file. | |
11 | ||
12 | Reading from it returns a list of supported sleep states, encoded as: | |
13 | ||
14 | 'freeze' (Suspend-to-Idle) | |
15 | 'standby' (Power-On Suspend) | |
16 | 'mem' (Suspend-to-RAM) | |
17 | 'disk' (Suspend-to-Disk) | |
18 | ||
19 | Suspend-to-Idle is always supported. Suspend-to-Disk is always supported | |
20 | too as long the kernel has been configured to support hibernation at all | |
21 | (ie. CONFIG_HIBERNATION is set in the kernel configuration file). Support | |
22 | for Suspend-to-RAM and Power-On Suspend depends on the capabilities of the | |
23 | platform. | |
24 | ||
25 | If one of the strings listed in /sys/power/state is written to it, the system | |
26 | will attempt to transition into the corresponding sleep state. Refer to | |
3ba9b1b8 TS |
27 | Documentation/admin-guide/pm/sleep-states.rst for a description of each of |
28 | those states. | |
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29 | |
30 | /sys/power/disk controls the operating mode of hibernation (Suspend-to-Disk). | |
31 | Specifically, it tells the kernel what to do after creating a hibernation image. | |
32 | ||
33 | Reading from it returns a list of supported options encoded as: | |
34 | ||
35 | 'platform' (put the system into sleep using a platform-provided method) | |
36 | 'shutdown' (shut the system down) | |
37 | 'reboot' (reboot the system) | |
38 | 'suspend' (trigger a Suspend-to-RAM transition) | |
39 | 'test_resume' (resume-after-hibernation test mode) | |
40 | ||
41 | The currently selected option is printed in square brackets. | |
42 | ||
43 | The 'platform' option is only available if the platform provides a special | |
44 | mechanism to put the system to sleep after creating a hibernation image (ACPI | |
45 | does that, for example). The 'suspend' option is available if Suspend-to-RAM | |
4493c1f0 | 46 | is supported. Refer to Documentation/power/basic-pm-debugging.txt for the |
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47 | description of the 'test_resume' option. |
48 | ||
49 | To select an option, write the string representing it to /sys/power/disk. | |
50 | ||
51 | /sys/power/image_size controls the size of hibernation images. | |
52 | ||
53 | It can be written a string representing a non-negative integer that will be | |
54 | used as a best-effort upper limit of the image size, in bytes. The hibernation | |
55 | core will do its best to ensure that the image size will not exceed that number. | |
56 | However, if that turns out to be impossible to achieve, a hibernation image will | |
57 | still be created and its size will be as small as possible. In particular, | |
58 | writing '0' to this file will enforce hibernation images to be as small as | |
59 | possible. | |
60 | ||
61 | Reading from this file returns the current image size limit, which is set to | |
62 | around 2/5 of available RAM by default. | |
63 | ||
64 | /sys/power/pm_trace controls the PM trace mechanism saving the last suspend | |
65 | or resume event point in the RTC across reboots. | |
66 | ||
67 | It helps to debug hard lockups or reboots due to device driver failures that | |
68 | occur during system suspend or resume (which is more common) more effectively. | |
69 | ||
70 | If /sys/power/pm_trace contains '1', the fingerprint of each suspend/resume | |
71 | event point in turn will be stored in the RTC memory (overwriting the actual | |
72 | RTC information), so it will survive a system crash if one occurs right after | |
73 | storing it and it can be used later to identify the driver that caused the crash | |
74 | to happen (see Documentation/power/s2ram.txt for more information). | |
75 | ||
76 | Initially it contains '0' which may be changed to '1' by writing a string | |
77 | representing a nonzero integer into it. |