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84ed64ee RW |
1 | What: /sys/power/ |
2 | Date: August 2006 | |
3 | Contact: Rafael J. Wysocki <rjw@sisk.pl> | |
4 | Description: | |
5 | The /sys/power directory will contain files that will | |
6 | provide a unified interface to the power management | |
7 | subsystem. | |
8 | ||
9 | What: /sys/power/state | |
10 | Date: August 2006 | |
11 | Contact: Rafael J. Wysocki <rjw@sisk.pl> | |
12 | Description: | |
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 | ||
23 | What: /sys/power/disk | |
24 | Date: August 2006 | |
25 | Contact: Rafael J. Wysocki <rjw@sisk.pl> | |
26 | Description: | |
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 | The suspend-to-disk method may be chosen by writing to this | |
43 | file one of the accepted strings: | |
44 | ||
45 | 'firmware' | |
46 | 'platform' | |
47 | 'shutdown' | |
48 | 'reboot' | |
49 | ||
50 | It will only change to 'firmware' or 'platform' if the system | |
51 | supports that. | |
52 | ||
53 | What: /sys/power/image_size | |
54 | Date: August 2006 | |
55 | Contact: Rafael J. Wysocki <rjw@sisk.pl> | |
56 | Description: | |
57 | The /sys/power/image_size file controls the size of the image | |
58 | created by the suspend-to-disk mechanism. It can be written a | |
59 | string representing a non-negative integer that will be used | |
60 | as an upper limit of the image size, in bytes. The kernel's | |
61 | suspend-to-disk code will do its best to ensure the image size | |
62 | will not exceed this number. However, if it turns out to be | |
63 | impossible, the kernel will try to suspend anyway using the | |
64 | smallest image possible. In particular, if "0" is written to | |
65 | this file, the suspend image will be as small as possible. | |
66 | ||
67 | Reading from this file will display the current image size | |
68 | limit, which is set to 500 MB by default. | |
69 | ||
70 | What: /sys/power/pm_trace | |
71 | Date: August 2006 | |
72 | Contact: Rafael J. Wysocki <rjw@sisk.pl> | |
73 | Description: | |
74 | The /sys/power/pm_trace file controls the code which saves the | |
75 | last PM event point in the RTC across reboots, so that you can | |
76 | debug a machine that just hangs during suspend (or more | |
77 | commonly, during resume). Namely, the RTC is only used to save | |
78 | the last PM event point if this file contains '1'. Initially | |
79 | it contains '0' which may be changed to '1' by writing a | |
80 | string representing a nonzero integer into it. | |
81 | ||
82 | To use this debugging feature you should attempt to suspend | |
83 | the machine, then reboot it and run | |
84 | ||
85 | dmesg -s 1000000 | grep 'hash matches' | |
86 | ||
87 | CAUTION: Using it will cause your machine's real-time (CMOS) | |
88 | clock to be set to a random invalid time after a resume. |