| Rafael J. Wysocki | 971cb7f | 2010-01-23 22:03:22 +0100 | [diff] [blame] | 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. |
| Rafael J. Wysocki | 5a2eb85 | 2010-01-23 22:25:23 +0100 | [diff] [blame] | 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. |