From 849369d6c66d3054688672f97d31fceb8e8230fb Mon Sep 17 00:00:00 2001 From: root Date: Fri, 25 Dec 2015 04:40:36 +0000 Subject: initial_commit --- Documentation/power/interface.txt | 75 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 75 insertions(+) create mode 100644 Documentation/power/interface.txt (limited to 'Documentation/power/interface.txt') diff --git a/Documentation/power/interface.txt b/Documentation/power/interface.txt new file mode 100644 index 00000000..c537834a --- /dev/null +++ b/Documentation/power/interface.txt @@ -0,0 +1,75 @@ +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 '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. -- cgit v1.2.3