Commit | Line | Data |
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971cb7fb RW |
1 | What: /sys/devices/.../power/ |
2 | Date: January 2009 | |
3 | Contact: Rafael J. Wysocki <rjw@sisk.pl> | |
4 | Description: | |
5 | The /sys/devices/.../power directory contains attributes | |
6 | allowing the user space to check and modify some power | |
7 | management related properties of given device. | |
8 | ||
9 | What: /sys/devices/.../power/wakeup | |
10 | Date: January 2009 | |
11 | Contact: Rafael J. Wysocki <rjw@sisk.pl> | |
12 | Description: | |
13 | The /sys/devices/.../power/wakeup attribute allows the user | |
14 | space to check if the device is enabled to wake up the system | |
15 | from sleep states, such as the memory sleep state (suspend to | |
16 | RAM) and hibernation (suspend to disk), and to enable or disable | |
17 | it to do that as desired. | |
18 | ||
19 | Some devices support "wakeup" events, which are hardware signals | |
20 | used to activate the system from a sleep state. Such devices | |
21 | have one of the following two values for the sysfs power/wakeup | |
22 | file: | |
23 | ||
24 | + "enabled\n" to issue the events; | |
25 | + "disabled\n" not to do so; | |
26 | ||
27 | In that cases the user space can change the setting represented | |
28 | by the contents of this file by writing either "enabled", or | |
29 | "disabled" to it. | |
30 | ||
31 | For the devices that are not capable of generating system wakeup | |
32 | events this file contains "\n". In that cases the user space | |
33 | cannot modify the contents of this file and the device cannot be | |
34 | enabled to wake up the system. | |
35 | ||
36 | What: /sys/devices/.../power/control | |
37 | Date: January 2009 | |
38 | Contact: Rafael J. Wysocki <rjw@sisk.pl> | |
39 | Description: | |
40 | The /sys/devices/.../power/control attribute allows the user | |
41 | space to control the run-time power management of the device. | |
42 | ||
43 | All devices have one of the following two values for the | |
44 | power/control file: | |
45 | ||
46 | + "auto\n" to allow the device to be power managed at run time; | |
47 | + "on\n" to prevent the device from being power managed; | |
48 | ||
49 | The default for all devices is "auto", which means that they may | |
50 | be subject to automatic power management, depending on their | |
51 | drivers. Changing this attribute to "on" prevents the driver | |
52 | from power managing the device at run time. Doing that while | |
53 | the device is suspended causes it to be woken up. | |
5a2eb858 RW |
54 | |
55 | What: /sys/devices/.../power/async | |
56 | Date: January 2009 | |
57 | Contact: Rafael J. Wysocki <rjw@sisk.pl> | |
58 | Description: | |
59 | The /sys/devices/.../async attribute allows the user space to | |
60 | enable or diasble the device's suspend and resume callbacks to | |
61 | be executed asynchronously (ie. in separate threads, in parallel | |
62 | with the main suspend/resume thread) during system-wide power | |
63 | transitions (eg. suspend to RAM, hibernation). | |
64 | ||
65 | All devices have one of the following two values for the | |
66 | power/async file: | |
67 | ||
68 | + "enabled\n" to permit the asynchronous suspend/resume; | |
69 | + "disabled\n" to forbid it; | |
70 | ||
71 | The value of this attribute may be changed by writing either | |
72 | "enabled", or "disabled" to it. | |
73 | ||
74 | It generally is unsafe to permit the asynchronous suspend/resume | |
75 | of a device unless it is certain that all of the PM dependencies | |
76 | of the device are known to the PM core. However, for some | |
77 | devices this attribute is set to "enabled" by bus type code or | |
78 | device drivers and in that cases it should be safe to leave the | |
79 | default value. |