Commit 0399d4db authored by Rafael J. Wysocki's avatar Rafael J. Wysocki
Browse files

PM / sleep: Introduce command line argument for sleep state enumeration 



On some systems the platform doesn't support neither
PM_SUSPEND_MEM nor PM_SUSPEND_STANDBY, so PM_SUSPEND_FREEZE is the
only available system sleep state.  However, some user space frameworks
only use the "mem" and (sometimes) "standby" sleep state labels, so
the users of those systems need to modify user space in order to be
able to use system suspend at all and that is not always possible.

For this reason, add a new kernel command line argument,
relative_sleep_states, allowing the users of those systems to change
the way in which the kernel assigns labels to system sleep states.
Namely, for relative_sleep_states=1, the "mem", "standby" and "freeze"
labels will enumerate the available system sleem states from the
deepest to the shallowest, respectively, so that "mem" is always
present in /sys/power/state and the other state strings may or may
not be presend depending on what is supported by the platform.

Update system sleep states documentation to reflect this change.

Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent 43e8317b

Documentation/ABI/testing/sysfs-power

+20 −9
Original line number Diff line number Diff line
@@ -7,19 +7,30 @@ Description: 
		subsystem.



What:		/sys/power/state

Date:		August 2006

Date:		May 2014

Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>

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 'freeze' (Low-Power Idle), 'standby'

		(Power-On Suspend), 'mem' (Suspend-to-RAM), and 'disk'

		(Suspend-to-Disk).

		The /sys/power/state file controls system sleep states.

		Reading from this file returns the available sleep state

		labels, which may be "mem", "standby", "freeze" and "disk"

		(hibernation).  The meanings of the first three labels depend on

		the relative_sleep_states command line argument as follows:

		 1) relative_sleep_states = 1

		    "mem", "standby", "freeze" represent non-hibernation sleep

		    states from the deepest ("mem", always present) to the

		    shallowest ("freeze").  "standby" and "freeze" may or may

		    not be present depending on the capabilities of the

		    platform.  "freeze" can only be present if "standby" is

		    present.

		 2) relative_sleep_states = 0 (default)

		    "mem" - "suspend-to-RAM", present if supported.

		    "standby" - "power-on suspend", present if supported.

		    "freeze" - "suspend-to-idle", always present.



		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.

		transition into the corresponding state, if available.  See

		Documentation/power/states.txt for a description of what

		"suspend-to-RAM", "power-on suspend" and "suspend-to-idle" mean.



What:		/sys/power/disk

Date:		September 2006

Documentation/kernel-parameters.txt

+7 −0
Original line number Diff line number Diff line
@@ -2889,6 +2889,13 @@ bytes respectively. Such letter suffixes can also be entirely omitted. 
			[KNL, SMP] Set scheduler's default relax_domain_level.

			See Documentation/cgroups/cpusets.txt.



	relative_sleep_states=

			[SUSPEND] Use sleep state labeling where the deepest

			state available other than hibernation is always "mem".

			Format: { "0" | "1" }

			0 -- Traditional sleep state labels.

			1 -- Relative sleep state labels.



	reserve=	[KNL,BUGS] Force the kernel to ignore some iomem area



	reservetop=	[X86-32]

Documentation/power/states.txt

+56 −31
Original line number Diff line number Diff line 
System Power Management Sleep States



System Power Management States

(C) 2014 Intel Corp., Rafael J. Wysocki <rafael.j.wysocki@intel.com>



The kernel supports up to four system sleep states generically, although three

of them depend on the platform support code to implement the low-level details

for each state.



The kernel supports four power management states generically, though

one is generic and the other three are dependent on platform support

code to implement the low-level details for each state.

This file describes each state, what they are

commonly called, what ACPI state they map to, and what string to write

to /sys/power/state to enter that state

The states are represented by strings that can be read or written to the

/sys/power/state file.  Those strings may be "mem", "standby", "freeze" and

"disk", where the last one always represents hibernation (Suspend-To-Disk) and

the meaning of the remaining ones depends on the relative_sleep_states command

line argument.



state:		Freeze / Low-Power Idle

For relative_sleep_states=1, the strings "mem", "standby" and "freeze" label the

available non-hibernation sleep states from the deepest to the shallowest,

respectively.  In that case, "mem" is always present in /sys/power/state,

because there is at least one non-hibernation sleep state in every system.  If

the given system supports two non-hibernation sleep states, "standby" is present

in /sys/power/state in addition to "mem".  If the system supports three

non-hibernation sleep states, "freeze" will be present in /sys/power/state in

addition to "mem" and "standby".



For relative_sleep_states=0, which is the default, the following descriptions

apply.



state:		Suspend-To-Idle

ACPI state:	S0

String:		"freeze"

Label:		"freeze"



This state is a generic, pure software, light-weight, low-power state.

It allows more energy to be saved relative to idle by freezing user

This state is a generic, pure software, light-weight, system sleep state.

It allows more energy to be saved relative to runtime idle by freezing user

space and putting all I/O devices into low-power states (possibly

lower-power than available at run time), such that the processors can

spend more time in their idle states.

This state can be used for platforms without Standby/Suspend-to-RAM



This state can be used for platforms without Power-On Suspend/Suspend-to-RAM

support, or it can be used in addition to Suspend-to-RAM (memory sleep)

to provide reduced resume latency.

to provide reduced resume latency.  It is always supported.





State:		Standby / Power-On Suspend

ACPI State:	S1

String:		"standby"

Label:		"standby"



This state offers minimal, though real, power savings, while providing

a very low-latency transition back to a working system. No operating

state is lost (the CPU retains power), so the system easily starts up

This state, if supported, offers moderate, though real, power savings, while

providing a relatively low-latency transition back to a working system.  No

operating state is lost (the CPU retains power), so the system easily starts up

again where it left off. 



We try to put devices in a low-power state equivalent to D1, which

also offers low power savings, but low resume latency. Not all devices

support D1, and those that don't are left on. 

In addition to freezing user space and putting all I/O devices into low-power

states, which is done for Suspend-To-Idle too, nonboot CPUs are taken offline

and all low-level system functions are suspended during transitions into this

state.  For this reason, it should allow more energy to be saved relative to

Suspend-To-Idle, but the resume latency will generally be greater than for that

state.





State:		Suspend-to-RAM

ACPI State:	S3

String:		"mem"

Label:		"mem"



This state offers significant power savings as everything in the

system is put into a low-power state, except for memory, which is

placed in self-refresh mode to retain its contents. 

This state, if supported, offers significant power savings as everything in the

system is put into a low-power state, except for memory, which should be placed

into the self-refresh mode to retain its contents.  All of the steps carried out

when entering Power-On Suspend are also carried out during transitions to STR.

Additional operations may take place depending on the platform capabilities.  In

particular, on ACPI systems the kernel passes control to the BIOS (platform

firmware) as the last step during STR transitions and that usually results in

powering down some more low-level components that aren't directly controlled by

the kernel.



System and device state is saved and kept in memory. All devices are

suspended and put into D3. In many cases, all peripheral buses lose

power when entering STR, so devices must be able to handle the

transition back to the On state. 

System and device state is saved and kept in memory.  All devices are suspended

and put into low-power states.  In many cases, all peripheral buses lose power

when entering STR, so devices must be able to handle the transition back to the

"on" state.



For at least ACPI, STR requires some minimal boot-strapping code to

resume the system from STR. This may be true on other platforms. 

For at least ACPI, STR requires some minimal boot-strapping code to resume the

system from it.  This may be the case on other platforms too.





State:		Suspend-to-disk

ACPI State:	S4

String:		"disk"

Label:		"disk"



This state offers the greatest power savings, and can be used even in

the absence of low-level platform support for power management. This

kernel/power/main.c

+6 −6
Original line number Diff line number Diff line
@@ -279,14 +279,14 @@ static inline void pm_print_times_init(void) {} 
struct kobject *power_kobj;



/**

 *	state - control system power state.

 * state - control system sleep states.

 *

 *	show() returns what states are supported, which is hard-coded to

 *	'freeze' (Low-Power Idle), 'standby' (Power-On Suspend),

 *	'mem' (Suspend-to-RAM), and 'disk' (Suspend-to-Disk).

 * show() returns available sleep state labels, which may be "mem", "standby",

 * "freeze" and "disk" (hibernation).  See Documentation/power/states.txt for a

 * description of what they mean.

 *

 *	store() accepts one of those strings, translates it into the

 *	proper enumerated value, and initiates a suspend transition.

 * store() accepts one of those strings, translates it into the proper

 * enumerated value, and initiates a suspend transition.

 */

static ssize_t state_show(struct kobject *kobj, struct kobj_attribute *attr,

			  char *buf)

kernel/power/suspend.c

+30 −2
Original line number Diff line number Diff line
@@ -78,6 +78,26 @@ static bool valid_state(suspend_state_t state) 
	return suspend_ops && suspend_ops->valid && suspend_ops->valid(state);

}



/*

 * If this is set, the "mem" label always corresponds to the deepest sleep state

 * available, the "standby" label corresponds to the second deepest sleep state

 * available (if any), and the "freeze" label corresponds to the remaining

 * available sleep state (if there is one).

 */

static bool relative_states;



static int __init sleep_states_setup(char *str)

{

	relative_states = !strncmp(str, "1", 1);

	if (relative_states) {

		pm_states[PM_SUSPEND_MEM].state = PM_SUSPEND_FREEZE;

		pm_states[PM_SUSPEND_FREEZE].state = 0;

	}

	return 1;

}



__setup("relative_sleep_states=", sleep_states_setup);



/**

 * suspend_set_ops - Set the global suspend method table.

 * @ops: Suspend operations to use.
@@ -85,12 +105,20 @@ static bool valid_state(suspend_state_t state) 
void suspend_set_ops(const struct platform_suspend_ops *ops)

{

	suspend_state_t i;

	int j = PM_SUSPEND_MAX - 1;



	lock_system_sleep();



	suspend_ops = ops;

	for (i = PM_SUSPEND_STANDBY; i <= PM_SUSPEND_MEM; i++)

		pm_states[i].state = valid_state(i) ? i : 0;

	for (i = PM_SUSPEND_MEM; i >= PM_SUSPEND_STANDBY; i--)

		if (valid_state(i))

			pm_states[j--].state = i;

		else if (!relative_states)

			pm_states[j--].state = 0;



	pm_states[j--].state = PM_SUSPEND_FREEZE;

	while (j >= PM_SUSPEND_MIN)

		pm_states[j--].state = 0;



	unlock_system_sleep();

}

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