1What:		/sys/power/
2Date:		August 2006
3Contact:	Rafael J. Wysocki <rjw@sisk.pl>
4Description:
5		The /sys/power directory will contain files that will
6		provide a unified interface to the power management
7		subsystem.
8
9What:		/sys/power/state
10Date:		August 2006
11Contact:	Rafael J. Wysocki <rjw@sisk.pl>
12Description:
13		The /sys/power/state file controls the system power state.
14		Reading from this file returns what states are supported,
15		which is hard-coded to 'standby' (Power-On Suspend), 'mem'
16		(Suspend-to-RAM), and 'disk' (Suspend-to-Disk).
17
18		Writing to this file one of these strings causes the system to
19		transition into that state. Please see the file
20		Documentation/power/states.txt for a description of each of
21		these states.
22
23What:		/sys/power/disk
24Date:		September 2006
25Contact:	Rafael J. Wysocki <rjw@sisk.pl>
26Description:
27		The /sys/power/disk file controls the operating mode of the
28		suspend-to-disk mechanism.  Reading from this file returns
29		the name of the method by which the system will be put to
30		sleep on the next suspend.  There are four methods supported:
31		'firmware' - means that the memory image will be saved to disk
32		by some firmware, in which case we also assume that the
33		firmware will handle the system suspend.
34		'platform' - the memory image will be saved by the kernel and
35		the system will be put to sleep by the platform driver (e.g.
36		ACPI or other PM registers).
37		'shutdown' - the memory image will be saved by the kernel and
38		the system will be powered off.
39		'reboot' - the memory image will be saved by the kernel and
40		the system will be rebooted.
41
42		Additionally, /sys/power/disk can be used to turn on one of the
43		two testing modes of the suspend-to-disk mechanism: 'testproc'
44		or 'test'.  If the suspend-to-disk mechanism is in the
45		'testproc' mode, writing 'disk' to /sys/power/state will cause
46		the kernel to disable nonboot CPUs and freeze tasks, wait for 5
47		seconds, unfreeze tasks and enable nonboot CPUs.  If it is in
48		the 'test' mode, writing 'disk' to /sys/power/state will cause
49		the kernel to disable nonboot CPUs and freeze tasks, shrink
50		memory, suspend devices, wait for 5 seconds, resume devices,
51		unfreeze tasks and enable nonboot CPUs.  Then, we are able to
52		look in the log messages and work out, for example, which code
53		is being slow and which device drivers are misbehaving.
54
55		The suspend-to-disk method may be chosen by writing to this
56		file one of the accepted strings:
57
58		'firmware'
59		'platform'
60		'shutdown'
61		'reboot'
62		'testproc'
63		'test'
64
65		It will only change to 'firmware' or 'platform' if the system
66		supports that.
67
68What:		/sys/power/image_size
69Date:		August 2006
70Contact:	Rafael J. Wysocki <rjw@sisk.pl>
71Description:
72		The /sys/power/image_size file controls the size of the image
73		created by the suspend-to-disk mechanism.  It can be written a
74		string representing a non-negative integer that will be used
75		as an upper limit of the image size, in bytes.  The kernel's
76		suspend-to-disk code will do its best to ensure the image size
77		will not exceed this number.  However, if it turns out to be
78		impossible, the kernel will try to suspend anyway using the
79		smallest image possible.  In particular, if "0" is written to
80		this file, the suspend image will be as small as possible.
81
82		Reading from this file will display the current image size
83		limit, which is set to 500 MB by default.
84
85What:		/sys/power/pm_trace
86Date:		August 2006
87Contact:	Rafael J. Wysocki <rjw@sisk.pl>
88Description:
89		The /sys/power/pm_trace file controls the code which saves the
90		last PM event point in the RTC across reboots, so that you can
91		debug a machine that just hangs during suspend (or more
92		commonly, during resume).  Namely, the RTC is only used to save
93		the last PM event point if this file contains '1'.  Initially
94		it contains '0' which may be changed to '1' by writing a
95		string representing a nonzero integer into it.
96
97		To use this debugging feature you should attempt to suspend
98		the machine, then reboot it and run
99
100		dmesg -s 1000000 | grep 'hash matches'
101
102		CAUTION: Using it will cause your machine's real-time (CMOS)
103		clock to be set to a random invalid time after a resume.
104