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PM / sleep: Update some system sleep documentation
Update some documentation related to system sleep to document new features and remove outdated information from it. Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Acked-by: Pavel Machek <pavel@ucw.cz> Reviewed-by: Chen Yu <yu.c.chen@intel.com>
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Rafael J. Wysocki
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@ -164,7 +164,32 @@ load n/2 modules more and try again.
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Again, if you find the offending module(s), it(they) must be unloaded every time
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before hibernation, and please report the problem with it(them).
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c) Advanced debugging
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c) Using the "test_resume" hibernation option
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/sys/power/disk generally tells the kernel what to do after creating a
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hibernation image. One of the available options is "test_resume" which
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causes the just created image to be used for immediate restoration. Namely,
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after doing:
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# echo test_resume > /sys/power/disk
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# echo disk > /sys/power/state
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a hibernation image will be created and a resume from it will be triggered
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immediately without involving the platform firmware in any way.
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That test can be used to check if failures to resume from hibernation are
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related to bad interactions with the platform firmware. That is, if the above
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works every time, but resume from actual hibernation does not work or is
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unreliable, the platform firmware may be responsible for the failures.
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On architectures and platforms that support using different kernels to restore
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hibernation images (that is, the kernel used to read the image from storage and
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load it into memory is different from the one included in the image) or support
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kernel address space randomization, it also can be used to check if failures
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to resume may be related to the differences between the restore and image
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kernels.
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d) Advanced debugging
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In case that hibernation does not work on your system even in the minimal
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configuration and compiling more drivers as modules is not practical or some
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@ -1,75 +1,76 @@
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Power Management Interface
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Power Management Interface for System Sleep
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Copyright (c) 2016 Intel Corp., Rafael J. Wysocki <rafael.j.wysocki@intel.com>
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The power management subsystem provides a unified sysfs interface to
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userspace, regardless of what architecture or platform one is
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running. The interface exists in /sys/power/ directory (assuming sysfs
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is mounted at /sys).
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The power management subsystem provides userspace with a unified sysfs interface
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for system sleep regardless of the underlying system architecture or platform.
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The interface is located in the /sys/power/ directory (assuming that sysfs is
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mounted at /sys).
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/sys/power/state controls system power state. Reading from this file
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returns what states are supported, which is hard-coded to 'freeze',
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'standby' (Power-On Suspend), 'mem' (Suspend-to-RAM), and 'disk'
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(Suspend-to-Disk).
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/sys/power/state is the system sleep state control file.
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Writing to this file one of those 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 those
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states.
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Reading from it returns a list of supported sleep states, encoded as:
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'freeze' (Suspend-to-Idle)
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'standby' (Power-On Suspend)
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'mem' (Suspend-to-RAM)
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'disk' (Suspend-to-Disk)
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/sys/power/disk controls the operating mode of the suspend-to-disk
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mechanism. Suspend-to-disk can be handled in several ways. We have a
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few options for putting the system to sleep - using the platform driver
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(e.g. ACPI or other suspend_ops), powering off the system or rebooting the
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system (for testing).
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Suspend-to-Idle is always supported. Suspend-to-Disk is always supported
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too as long the kernel has been configured to support hibernation at all
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(ie. CONFIG_HIBERNATION is set in the kernel configuration file). Support
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for Suspend-to-RAM and Power-On Suspend depends on the capabilities of the
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platform.
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Additionally, /sys/power/disk can be used to turn on one of the two testing
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modes of the suspend-to-disk mechanism: 'testproc' or 'test'. If the
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suspend-to-disk mechanism is in the 'testproc' mode, writing 'disk' to
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/sys/power/state will cause the kernel to disable nonboot CPUs and freeze
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tasks, wait for 5 seconds, unfreeze tasks and enable nonboot CPUs. If it is
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in the 'test' mode, writing 'disk' to /sys/power/state will cause the kernel
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to disable nonboot CPUs and freeze tasks, shrink memory, suspend devices, wait
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for 5 seconds, resume devices, unfreeze tasks and enable nonboot CPUs. Then,
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we are able to 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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If one of the strings listed in /sys/power/state is written to it, the system
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will attempt to transition into the corresponding sleep state. Refer to
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Documentation/power/states.txt for a description of each of those states.
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Reading from this file will display all supported modes and the currently
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selected one in brackets, for example
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/sys/power/disk controls the operating mode of hibernation (Suspend-to-Disk).
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Specifically, it tells the kernel what to do after creating a hibernation image.
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[shutdown] reboot test testproc
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Reading from it returns a list of supported options encoded as:
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Writing to this file will accept one of
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'platform' (put the system into sleep using a platform-provided method)
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'shutdown' (shut the system down)
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'reboot' (reboot the system)
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'suspend' (trigger a Suspend-to-RAM transition)
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'test_resume' (resume-after-hibernation test mode)
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'platform' (only if the platform supports it)
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'shutdown'
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'reboot'
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'testproc'
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'test'
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The currently selected option is printed in square brackets.
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/sys/power/image_size controls the size of the image created by
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the suspend-to-disk mechanism. It can be written a string
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representing a non-negative integer that will be used as an upper
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limit of the image size, in bytes. The suspend-to-disk mechanism will
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do its best to ensure the image size will not exceed that number. However,
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if this turns out to be impossible, it will try to suspend anyway using the
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smallest image possible. In particular, if "0" is written to this file, the
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suspend image will be as small as possible.
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The 'platform' option is only available if the platform provides a special
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mechanism to put the system to sleep after creating a hibernation image (ACPI
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does that, for example). The 'suspend' option is available if Suspend-to-RAM
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is supported. Refer to Documentation/power/basic_pm_debugging.txt for the
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description of the 'test_resume' option.
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Reading from this file will display the current image size limit, which
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is set to 2/5 of available RAM by default.
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To select an option, write the string representing it to /sys/power/disk.
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/sys/power/pm_trace controls the code which saves the last PM event point in
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the RTC across reboots, so that you can debug a machine that just hangs
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during suspend (or more commonly, during resume). Namely, the RTC is only
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used to save the last PM event point if this file contains '1'. Initially it
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contains '0' which may be changed to '1' by writing a string representing a
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nonzero integer into it.
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/sys/power/image_size controls the size of hibernation images.
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To use this debugging feature you should attempt to suspend the machine, then
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reboot it and run
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It can be written a string representing a non-negative integer that will be
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used as a best-effort upper limit of the image size, in bytes. The hibernation
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core will do its best to ensure that the image size will not exceed that number.
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However, if that turns out to be impossible to achieve, a hibernation image will
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still be created and its size will be as small as possible. In particular,
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writing '0' to this file will enforce hibernation images to be as small as
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possible.
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dmesg -s 1000000 | grep 'hash matches'
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Reading from this file returns the current image size limit, which is set to
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around 2/5 of available RAM by default.
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CAUTION: Using it will cause your machine's real-time (CMOS) clock to be
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set to a random invalid time after a resume.
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/sys/power/pm_trace controls the PM trace mechanism saving the last suspend
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or resume event point in the RTC across reboots.
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It helps to debug hard lockups or reboots due to device driver failures that
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occur during system suspend or resume (which is more common) more effectively.
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If /sys/power/pm_trace contains '1', the fingerprint of each suspend/resume
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event point in turn will be stored in the RTC memory (overwriting the actual
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RTC information), so it will survive a system crash if one occurs right after
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storing it and it can be used later to identify the driver that caused the crash
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to happen (see Documentation/power/s2ram.txt for more information).
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Initially it contains '0' which may be changed to '1' by writing a string
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representing a nonzero integer into it.
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