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Diffstat (limited to 'Documentation/power/interface.txt')
| -rw-r--r-- | Documentation/power/interface.txt | 151 |
1 files changed, 76 insertions, 75 deletions
diff --git a/Documentation/power/interface.txt b/Documentation/power/interface.txt index f1f0f59a7c47..974916ff6608 100644 --- a/Documentation/power/interface.txt +++ b/Documentation/power/interface.txt @@ -1,75 +1,76 @@ -Power Management Interface - - -The power management subsystem provides a unified sysfs interface to -userspace, regardless of what architecture or platform one is -running. The interface exists in /sys/power/ directory (assuming sysfs -is mounted at /sys). - -/sys/power/state controls system power state. Reading from this file -returns what states are supported, which is hard-coded to 'freeze', -'standby' (Power-On Suspend), 'mem' (Suspend-to-RAM), and 'disk' -(Suspend-to-Disk). - -Writing to this file one of those strings causes the system to -transition into that state. Please see the file -Documentation/power/states.txt for a description of each of those -states. - - -/sys/power/disk controls the operating mode of the suspend-to-disk -mechanism. Suspend-to-disk can be handled in several ways. We have a -few options for putting the system to sleep - using the platform driver -(e.g. ACPI or other suspend_ops), powering off the system or rebooting the -system (for testing). - -Additionally, /sys/power/disk can be used to turn on one of the two testing -modes of the suspend-to-disk mechanism: 'testproc' or 'test'. If the -suspend-to-disk mechanism is in the 'testproc' mode, writing 'disk' to -/sys/power/state will cause the kernel to disable nonboot CPUs and freeze -tasks, wait for 5 seconds, unfreeze tasks and enable nonboot CPUs. If it is -in the 'test' mode, writing 'disk' to /sys/power/state will cause the kernel -to disable nonboot CPUs and freeze tasks, shrink memory, suspend devices, wait -for 5 seconds, resume devices, unfreeze tasks and enable nonboot CPUs. Then, -we are able to look in the log messages and work out, for example, which code -is being slow and which device drivers are misbehaving. - -Reading from this file will display all supported modes and the currently -selected one in brackets, for example - - [shutdown] reboot test testproc - -Writing to this file will accept one of - - 'platform' (only if the platform supports it) - 'shutdown' - 'reboot' - 'testproc' - 'test' - -/sys/power/image_size controls the size of the image created by -the suspend-to-disk mechanism. It can be written a string -representing a non-negative integer that will be used as an upper -limit of the image size, in bytes. The suspend-to-disk mechanism will -do its best to ensure the image size will not exceed that number. However, -if this turns out to be impossible, it will try to suspend anyway using the -smallest image possible. In particular, if "0" is written to this file, the -suspend image will be as small as possible. - -Reading from this file will display the current image size limit, which -is set to 2/5 of available RAM by default. - -/sys/power/pm_trace controls the code which saves the last PM event point in -the RTC across reboots, so that you can debug a machine that just hangs -during suspend (or more commonly, during resume). Namely, the RTC is only -used to save the last PM event point if this file contains '1'. Initially it -contains '0' which may be changed to '1' by writing a string representing a -nonzero integer into it. - -To use this debugging feature you should attempt to suspend the machine, then -reboot it and run - - dmesg -s 1000000 | grep 'hash matches' - -CAUTION: Using it will cause your machine's real-time (CMOS) clock to be -set to a random invalid time after a resume. +Power Management Interface for System Sleep + +Copyright (c) 2016 Intel Corp., Rafael J. Wysocki <rafael.j.wysocki@intel.com> + +The power management subsystem provides userspace with a unified sysfs interface +for system sleep regardless of the underlying system architecture or platform. +The interface is located in the /sys/power/ directory (assuming that sysfs is +mounted at /sys). + +/sys/power/state is the system sleep state control file. + +Reading from it returns a list of supported sleep states, encoded as: + +'freeze' (Suspend-to-Idle) +'standby' (Power-On Suspend) +'mem' (Suspend-to-RAM) +'disk' (Suspend-to-Disk) + +Suspend-to-Idle is always supported. Suspend-to-Disk is always supported +too as long the kernel has been configured to support hibernation at all +(ie. CONFIG_HIBERNATION is set in the kernel configuration file). Support +for Suspend-to-RAM and Power-On Suspend depends on the capabilities of the +platform. + +If one of the strings listed in /sys/power/state is written to it, the system +will attempt to transition into the corresponding sleep state. Refer to +Documentation/power/states.txt for a description of each of those states. + +/sys/power/disk controls the operating mode of hibernation (Suspend-to-Disk). +Specifically, it tells the kernel what to do after creating a hibernation image. + +Reading from it returns a list of supported options encoded as: + +'platform' (put the system into sleep using a platform-provided method) +'shutdown' (shut the system down) +'reboot' (reboot the system) +'suspend' (trigger a Suspend-to-RAM transition) +'test_resume' (resume-after-hibernation test mode) + +The currently selected option is printed in square brackets. + +The 'platform' option is only available if the platform provides a special +mechanism to put the system to sleep after creating a hibernation image (ACPI +does that, for example). The 'suspend' option is available if Suspend-to-RAM +is supported. Refer to Documentation/power/basic_pm_debugging.txt for the +description of the 'test_resume' option. + +To select an option, write the string representing it to /sys/power/disk. + +/sys/power/image_size controls the size of hibernation images. + +It can be written a string representing a non-negative integer that will be +used as a best-effort upper limit of the image size, in bytes. The hibernation +core will do its best to ensure that the image size will not exceed that number. +However, if that turns out to be impossible to achieve, a hibernation image will +still be created and its size will be as small as possible. In particular, +writing '0' to this file will enforce hibernation images to be as small as +possible. + +Reading from this file returns the current image size limit, which is set to +around 2/5 of available RAM by default. + +/sys/power/pm_trace controls the PM trace mechanism saving the last suspend +or resume event point in the RTC across reboots. + +It helps to debug hard lockups or reboots due to device driver failures that +occur during system suspend or resume (which is more common) more effectively. + +If /sys/power/pm_trace contains '1', the fingerprint of each suspend/resume +event point in turn will be stored in the RTC memory (overwriting the actual +RTC information), so it will survive a system crash if one occurs right after +storing it and it can be used later to identify the driver that caused the crash +to happen (see Documentation/power/s2ram.txt for more information). + +Initially it contains '0' which may be changed to '1' by writing a string +representing a nonzero integer into it. |