Based on kernel version 4.9. Page generated on 2016-12-21 14:36 EST.
1 Power Management Interface for System Sleep 2 3 Copyright (c) 2016 Intel Corp., Rafael J. Wysocki <email@example.com> 4 5 The power management subsystem provides userspace with a unified sysfs interface 6 for system sleep regardless of the underlying system architecture or platform. 7 The interface is located in the /sys/power/ directory (assuming that sysfs is 8 mounted at /sys). 9 10 /sys/power/state is the system sleep state control file. 11 12 Reading from it returns a list of supported sleep states, encoded as: 13 14 'freeze' (Suspend-to-Idle) 15 'standby' (Power-On Suspend) 16 'mem' (Suspend-to-RAM) 17 'disk' (Suspend-to-Disk) 18 19 Suspend-to-Idle is always supported. Suspend-to-Disk is always supported 20 too as long the kernel has been configured to support hibernation at all 21 (ie. CONFIG_HIBERNATION is set in the kernel configuration file). Support 22 for Suspend-to-RAM and Power-On Suspend depends on the capabilities of the 23 platform. 24 25 If one of the strings listed in /sys/power/state is written to it, the system 26 will attempt to transition into the corresponding sleep state. Refer to 27 Documentation/power/states.txt for a description of each of those states. 28 29 /sys/power/disk controls the operating mode of hibernation (Suspend-to-Disk). 30 Specifically, it tells the kernel what to do after creating a hibernation image. 31 32 Reading from it returns a list of supported options encoded as: 33 34 'platform' (put the system into sleep using a platform-provided method) 35 'shutdown' (shut the system down) 36 'reboot' (reboot the system) 37 'suspend' (trigger a Suspend-to-RAM transition) 38 'test_resume' (resume-after-hibernation test mode) 39 40 The currently selected option is printed in square brackets. 41 42 The 'platform' option is only available if the platform provides a special 43 mechanism to put the system to sleep after creating a hibernation image (ACPI 44 does that, for example). The 'suspend' option is available if Suspend-to-RAM 45 is supported. Refer to Documentation/power/basic_pm_debugging.txt for the 46 description of the 'test_resume' option. 47 48 To select an option, write the string representing it to /sys/power/disk. 49 50 /sys/power/image_size controls the size of hibernation images. 51 52 It can be written a string representing a non-negative integer that will be 53 used as a best-effort upper limit of the image size, in bytes. The hibernation 54 core will do its best to ensure that the image size will not exceed that number. 55 However, if that turns out to be impossible to achieve, a hibernation image will 56 still be created and its size will be as small as possible. In particular, 57 writing '0' to this file will enforce hibernation images to be as small as 58 possible. 59 60 Reading from this file returns the current image size limit, which is set to 61 around 2/5 of available RAM by default. 62 63 /sys/power/pm_trace controls the PM trace mechanism saving the last suspend 64 or resume event point in the RTC across reboots. 65 66 It helps to debug hard lockups or reboots due to device driver failures that 67 occur during system suspend or resume (which is more common) more effectively. 68 69 If /sys/power/pm_trace contains '1', the fingerprint of each suspend/resume 70 event point in turn will be stored in the RTC memory (overwriting the actual 71 RTC information), so it will survive a system crash if one occurs right after 72 storing it and it can be used later to identify the driver that caused the crash 73 to happen (see Documentation/power/s2ram.txt for more information). 74 75 Initially it contains '0' which may be changed to '1' by writing a string 76 representing a nonzero integer into it.