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| 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. | ||