| Rafael J. Wysocki | 84ed64e | 2006-08-30 23:38:06 +0200 | [diff] [blame] | 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. |