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1da177e4 LT |
1 | Power Management Interface |
2 | ||
3 | ||
4 | The power management subsystem provides a unified sysfs interface to | |
5 | userspace, regardless of what architecture or platform one is | |
6 | running. The interface exists in /sys/power/ directory (assuming sysfs | |
7 | is mounted at /sys). | |
8 | ||
9 | /sys/power/state controls system power state. Reading from this file | |
10 | returns what states are supported, which is hard-coded to 'standby' | |
11 | (Power-On Suspend), 'mem' (Suspend-to-RAM), and 'disk' | |
12 | (Suspend-to-Disk). | |
13 | ||
14 | Writing to this file one of those strings causes the system to | |
15 | transition into that state. Please see the file | |
16 | Documentation/power/states.txt for a description of each of those | |
17 | states. | |
18 | ||
19 | ||
20 | /sys/power/disk controls the operating mode of the suspend-to-disk | |
21 | mechanism. Suspend-to-disk can be handled in several ways. The | |
22 | greatest distinction is who writes memory to disk - the firmware or | |
23 | the kernel. If the firmware does it, we assume that it also handles | |
24 | suspending the system. | |
25 | ||
26 | If the kernel does it, then we have three options for putting the system | |
27 | to sleep - using the platform driver (e.g. ACPI or other PM | |
28 | registers), powering off the system or rebooting the system (for | |
29 | testing). The system will support either 'firmware' or 'platform', and | |
30 | that is known a priori. But, the user may choose 'shutdown' or | |
31 | 'reboot' as alternatives. | |
32 | ||
33 | Reading from this file will display what the mode is currently set | |
34 | to. Writing to this file will accept one of | |
35 | ||
36 | 'firmware' | |
37 | 'platform' | |
38 | 'shutdown' | |
39 | 'reboot' | |
40 | ||
41 | It will only change to 'firmware' or 'platform' if the system supports | |
42 | it. | |
43 | ||
ca0aec0f RW |
44 | /sys/power/image_size controls the size of the image created by |
45 | the suspend-to-disk mechanism. It can be written a string | |
46 | representing a non-negative integer that will be used as an upper | |
47 | limit of the image size, in megabytes. The suspend-to-disk mechanism will | |
48 | do its best to ensure the image size will not exceed that number. However, | |
49 | if this turns out to be impossible, it will try to suspend anyway using the | |
50 | smallest image possible. In particular, if "0" is written to this file, the | |
51 | suspend image will be as small as possible. | |
52 | ||
53 | Reading from this file will display the current image size limit, which | |
54 | is set to 500 MB by default. |