2006-08-31 05:38:06 +08:00
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What: /sys/power/
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Date: August 2006
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Contact: Rafael J. Wysocki <rjw@sisk.pl>
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Description:
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The /sys/power directory will contain files that will
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provide a unified interface to the power management
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subsystem.
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What: /sys/power/state
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Date: August 2006
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Contact: Rafael J. Wysocki <rjw@sisk.pl>
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Description:
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The /sys/power/state file controls the system power state.
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Reading from this file returns what states are supported,
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which is hard-coded to 'standby' (Power-On Suspend), 'mem'
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(Suspend-to-RAM), and 'disk' (Suspend-to-Disk).
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Writing to this file one of these strings causes the system to
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transition into that state. Please see the file
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Documentation/power/states.txt for a description of each of
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these states.
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What: /sys/power/disk
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2006-11-03 14:07:19 +08:00
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Date: September 2006
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2006-08-31 05:38:06 +08:00
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Contact: Rafael J. Wysocki <rjw@sisk.pl>
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Description:
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The /sys/power/disk file controls the operating mode of the
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suspend-to-disk mechanism. Reading from this file returns
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the name of the method by which the system will be put to
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sleep on the next suspend. There are four methods supported:
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'firmware' - means that the memory image will be saved to disk
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by some firmware, in which case we also assume that the
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firmware will handle the system suspend.
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'platform' - the memory image will be saved by the kernel and
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the system will be put to sleep by the platform driver (e.g.
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ACPI or other PM registers).
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'shutdown' - the memory image will be saved by the kernel and
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the system will be powered off.
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'reboot' - the memory image will be saved by the kernel and
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the system will be rebooted.
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2006-11-03 14:07:19 +08:00
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Additionally, /sys/power/disk can be used to turn on one of the
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two testing modes of the suspend-to-disk mechanism: 'testproc'
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or 'test'. If the suspend-to-disk mechanism is in the
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'testproc' mode, writing 'disk' to /sys/power/state will cause
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the kernel to disable nonboot CPUs and freeze tasks, wait for 5
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seconds, unfreeze tasks and enable nonboot CPUs. If it is in
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the 'test' mode, writing 'disk' to /sys/power/state will cause
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the kernel to disable nonboot CPUs and freeze tasks, shrink
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memory, suspend devices, wait for 5 seconds, resume devices,
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unfreeze tasks and enable nonboot CPUs. Then, we are able to
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look in the log messages and work out, for example, which code
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is being slow and which device drivers are misbehaving.
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2006-08-31 05:38:06 +08:00
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The suspend-to-disk method may be chosen by writing to this
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file one of the accepted strings:
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'firmware'
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'platform'
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'shutdown'
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'reboot'
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2006-11-03 14:07:19 +08:00
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'testproc'
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'test'
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2006-08-31 05:38:06 +08:00
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It will only change to 'firmware' or 'platform' if the system
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supports that.
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What: /sys/power/image_size
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Date: August 2006
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Contact: Rafael J. Wysocki <rjw@sisk.pl>
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Description:
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The /sys/power/image_size file controls the size of the image
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created by the suspend-to-disk mechanism. It can be written a
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string representing a non-negative integer that will be used
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as an upper limit of the image size, in bytes. The kernel's
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suspend-to-disk code will do its best to ensure the image size
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will not exceed this number. However, if it turns out to be
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impossible, the kernel will try to suspend anyway using the
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smallest image possible. In particular, if "0" is written to
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this file, the suspend image will be as small as possible.
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Reading from this file will display the current image size
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limit, which is set to 500 MB by default.
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What: /sys/power/pm_trace
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Date: August 2006
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Contact: Rafael J. Wysocki <rjw@sisk.pl>
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Description:
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The /sys/power/pm_trace file controls the code which saves the
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last PM event point in the RTC across reboots, so that you can
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debug a machine that just hangs during suspend (or more
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commonly, during resume). Namely, the RTC is only used to save
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the last PM event point if this file contains '1'. Initially
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it contains '0' which may be changed to '1' by writing a
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string representing a nonzero integer into it.
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To use this debugging feature you should attempt to suspend
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the machine, then reboot it and run
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dmesg -s 1000000 | grep 'hash matches'
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2010-10-12 06:00:25 +08:00
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If you do not get any matches (or they appear to be false
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positives), it is possible that the last PM event point
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referred to a device created by a loadable kernel module. In
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this case cat /sys/power/pm_trace_dev_match (see below) after
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your system is started up and the kernel modules are loaded.
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2006-08-31 05:38:06 +08:00
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CAUTION: Using it will cause your machine's real-time (CMOS)
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clock to be set to a random invalid time after a resume.
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2010-01-24 05:25:15 +08:00
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2010-10-12 06:00:25 +08:00
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What; /sys/power/pm_trace_dev_match
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Date: October 2010
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Contact: James Hogan <james@albanarts.com>
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Description:
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The /sys/power/pm_trace_dev_match file contains the name of the
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device associated with the last PM event point saved in the RTC
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across reboots when pm_trace has been used. More precisely it
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contains the list of current devices (including those
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registered by loadable kernel modules since boot) which match
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the device hash in the RTC at boot, with a newline after each
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one.
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The advantage of this file over the hash matches printed to the
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kernel log (see /sys/power/pm_trace), is that it includes
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devices created after boot by loadable kernel modules.
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Due to the small hash size necessary to fit in the RTC, it is
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possible that more than one device matches the hash, in which
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case further investigation is required to determine which
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device is causing the problem. Note that genuine RTC clock
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values (such as when pm_trace has not been used), can still
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match a device and output it's name here.
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2010-01-24 05:25:15 +08:00
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What: /sys/power/pm_async
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Date: January 2009
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Contact: Rafael J. Wysocki <rjw@sisk.pl>
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Description:
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The /sys/power/pm_async file controls the switch allowing the
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user space to enable or disable asynchronous suspend and resume
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of devices. If enabled, this feature will cause some device
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drivers' suspend and resume callbacks to be executed in parallel
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with each other and with the main suspend thread. It is enabled
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if this file contains "1", which is the default. It may be
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disabled by writing "0" to this file, in which case all devices
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will be suspended and resumed synchronously.
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PM: Make it possible to avoid races between wakeup and system sleep
One of the arguments during the suspend blockers discussion was that
the mainline kernel didn't contain any mechanisms making it possible
to avoid races between wakeup and system suspend.
Generally, there are two problems in that area. First, if a wakeup
event occurs exactly when /sys/power/state is being written to, it
may be delivered to user space right before the freezer kicks in, so
the user space consumer of the event may not be able to process it
before the system is suspended. Second, if a wakeup event occurs
after user space has been frozen, it is not generally guaranteed that
the ongoing transition of the system into a sleep state will be
aborted.
To address these issues introduce a new global sysfs attribute,
/sys/power/wakeup_count, associated with a running counter of wakeup
events and three helper functions, pm_stay_awake(), pm_relax(), and
pm_wakeup_event(), that may be used by kernel subsystems to control
the behavior of this attribute and to request the PM core to abort
system transitions into a sleep state already in progress.
The /sys/power/wakeup_count file may be read from or written to by
user space. Reads will always succeed (unless interrupted by a
signal) and return the current value of the wakeup events counter.
Writes, however, will only succeed if the written number is equal to
the current value of the wakeup events counter. If a write is
successful, it will cause the kernel to save the current value of the
wakeup events counter and to abort the subsequent system transition
into a sleep state if any wakeup events are reported after the write
has returned.
[The assumption is that before writing to /sys/power/state user space
will first read from /sys/power/wakeup_count. Next, user space
consumers of wakeup events will have a chance to acknowledge or
veto the upcoming system transition to a sleep state. Finally, if
the transition is allowed to proceed, /sys/power/wakeup_count will
be written to and if that succeeds, /sys/power/state will be written
to as well. Still, if any wakeup events are reported to the PM core
by kernel subsystems after that point, the transition will be
aborted.]
Additionally, put a wakeup events counter into struct dev_pm_info and
make these per-device wakeup event counters available via sysfs,
so that it's possible to check the activity of various wakeup event
sources within the kernel.
To illustrate how subsystems can use pm_wakeup_event(), make the
low-level PCI runtime PM wakeup-handling code use it.
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
Acked-by: markgross <markgross@thegnar.org>
Reviewed-by: Alan Stern <stern@rowland.harvard.edu>
2010-07-06 04:43:53 +08:00
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What: /sys/power/wakeup_count
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Date: July 2010
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Contact: Rafael J. Wysocki <rjw@sisk.pl>
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Description:
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The /sys/power/wakeup_count file allows user space to put the
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system into a sleep state while taking into account the
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concurrent arrival of wakeup events. Reading from it returns
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the current number of registered wakeup events and it blocks if
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some wakeup events are being processed at the time the file is
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read from. Writing to it will only succeed if the current
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number of wakeup events is equal to the written value and, if
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successful, will make the kernel abort a subsequent transition
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to a sleep state if any wakeup events are reported after the
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write has returned.
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