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What: /sys/power/
Date: August 2006
Contact: Rafael J. Wysocki <rjw@sisk.pl>
Description:
The /sys/power directory will contain files that will
provide a unified interface to the power management
subsystem.
What: /sys/power/state
Date: August 2006
Contact: Rafael J. Wysocki <rjw@sisk.pl>
Description:
The /sys/power/state file controls the 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 these strings causes the system to
transition into that state. Please see the file
Documentation/power/states.txt for a description of each of
these states.
What: /sys/power/disk
Date: September 2006
Contact: Rafael J. Wysocki <rjw@sisk.pl>
Description:
The /sys/power/disk file controls the operating mode of the
suspend-to-disk mechanism. Reading from this file returns
the name of the method by which the system will be put to
sleep on the next suspend. There are four methods supported:
'firmware' - means that the memory image will be saved to disk
by some firmware, in which case we also assume that the
firmware will handle the system suspend.
'platform' - the memory image will be saved by the kernel and
the system will be put to sleep by the platform driver (e.g.
ACPI or other PM registers).
'shutdown' - the memory image will be saved by the kernel and
the system will be powered off.
'reboot' - the memory image will be saved by the kernel and
the system will be rebooted.
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.
The suspend-to-disk method may be chosen by writing to this
file one of the accepted strings:
'firmware'
'platform'
'shutdown'
'reboot'
'testproc'
'test'
It will only change to 'firmware' or 'platform' if the system
supports that.
What: /sys/power/image_size
Date: August 2006
Contact: Rafael J. Wysocki <rjw@sisk.pl>
Description:
The /sys/power/image_size file 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 kernel's
suspend-to-disk code will do its best to ensure the image size
will not exceed this number. However, if it turns out to be
impossible, the kernel 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 500 MB by default.
What: /sys/power/pm_trace
Date: August 2006
Contact: Rafael J. Wysocki <rjw@sisk.pl>
Description:
The /sys/power/pm_trace file 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'
If you do not get any matches (or they appear to be false
positives), it is possible that the last PM event point
referred to a device created by a loadable kernel module. In
this case cat /sys/power/pm_trace_dev_match (see below) after
your system is started up and the kernel modules are loaded.
CAUTION: Using it will cause your machine's real-time (CMOS)
clock to be set to a random invalid time after a resume.
What; /sys/power/pm_trace_dev_match
Date: October 2010
Contact: James Hogan <james@albanarts.com>
Description:
The /sys/power/pm_trace_dev_match file contains the name of the
device associated with the last PM event point saved in the RTC
across reboots when pm_trace has been used. More precisely it
contains the list of current devices (including those
registered by loadable kernel modules since boot) which match
the device hash in the RTC at boot, with a newline after each
one.
The advantage of this file over the hash matches printed to the
kernel log (see /sys/power/pm_trace), is that it includes
devices created after boot by loadable kernel modules.
Due to the small hash size necessary to fit in the RTC, it is
possible that more than one device matches the hash, in which
case further investigation is required to determine which
device is causing the problem. Note that genuine RTC clock
values (such as when pm_trace has not been used), can still
match a device and output it's name here.
What: /sys/power/pm_async
Date: January 2009
Contact: Rafael J. Wysocki <rjw@sisk.pl>
Description:
The /sys/power/pm_async file controls the switch allowing the
user space to enable or disable asynchronous suspend and resume
of devices. If enabled, this feature will cause some device
drivers' suspend and resume callbacks to be executed in parallel
with each other and with the main suspend thread. It is enabled
if this file contains "1", which is the default. It may be
disabled by writing "0" to this file, in which case all devices
will be suspended and resumed synchronously.
What: /sys/power/wakeup_count
Date: July 2010
Contact: Rafael J. Wysocki <rjw@sisk.pl>
Description:
The /sys/power/wakeup_count file allows user space to put the
system into a sleep state while taking into account the
concurrent arrival of wakeup events. Reading from it returns
the current number of registered wakeup events and it blocks if
some wakeup events are being processed at the time the file is
read from. Writing to it will only succeed if the current
number of wakeup events is equal to the written value and, if
successful, will make the kernel abort a subsequent transition
to a sleep state if any wakeup events are reported after the
write has returned.
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