admin-guide/pm/sleep-states.rst

1 .. SPDX-License-Identifier: GPL-2.0
13 Sleep states are global low-power states of the entire system in which user
22 the Linux kernel can support up to four system sleep states, including
23 hibernation and up to three variants of system suspend.  The sleep states that
28 Suspend-to-Idle
29 ---------------
31 This is a generic, pure software, light-weight variant of system suspend (also
34 I/O devices into low-power states (possibly lower-power than available in the
38 The system is woken up from this state by in-band interrupts, so theoretically
40 also be set up as wakeup devices for S2Idle.
43 or :ref:`suspend-to-RAM <s2ram>`, or it can be used in addition to any of the
50 -------
54 operating state is lost (the system core logic retains power), so the system can
58 I/O devices into low-power states, which is done for :ref:`suspend-to-idle
59 <s2idle>` too, nonboot CPUs are taken offline and all low-level system functions
61 allow more energy to be saved relative to :ref:`suspend-to-idle <s2idle>`, but
64 The set of devices that can wake up the system from this state usually is
65 reduced relative to :ref:`suspend-to-idle <s2idle>` and it may be necessary to
66 rely on the platform for setting up the wakeup functionality as appropriate.
70 core system suspend subsystem.  On ACPI-based systems this state is mapped to
75 Suspend-to-RAM
76 --------------
79 energy savings as everything in the system is put into a low-power state, except
80 for memory, which should be placed into the self-refresh mode to retain its
83 take place depending on the platform capabilities.  In particular, on ACPI-based
86 more low-level components that are not directly controlled by the kernel.
89 suspended and put into low-power states.  In many cases, all peripheral buses
90 lose power when entering S2RAM, so devices must be able to handle the transition
93 On ACPI-based systems S2RAM requires some minimal boot-strapping code in the
97 The set of devices that can wake up the system from S2RAM usually is reduced
98 relative to :ref:`suspend-to-idle <s2idle>` and :ref:`standby <standby>` and it
99 may be necessary to rely on the platform for setting up the wakeup functionality
104 suspend subsystem.  On ACPI-based systems it is mapped to the S3 system state
110 -----------
112 This state (also referred to as Suspend-to-Disk or STD) offers the greatest
113 energy savings and can be used even in the absence of low-level platform support
114 for system suspend.  However, it requires some low-level code for resuming the
124 is written out and finally the system goes into the target low-power state in
125 which power is cut from almost all of its hardware components, including memory,
129 special low-power state (like ACPI S4), or it may simply power down itself.
130 Powering down means minimum power draw and it allows this mechanism to work on
131 any system.  However, entering a special low-power state may allow additional
144 the special architecture-specific low-level code is needed.  Finally, the
145 image kernel restores the system to the pre-hibernation state and allows user
150 for the given CPU architecture includes the low-level code for system resume.
156 The power management subsystem provides userspace with a unified ``sysfs``
158 platform.  That interface is located in the :file:`/sys/power/` directory
169 	:ref:`hibernation <hibernation>`, :ref:`suspend-to-idle <s2idle>` and
183 	and "deep".  The "s2idle" string always represents :ref:`suspend-to-idle
185 	:ref:`standby <standby>` and :ref:`suspend-to-RAM <s2ram>`,
197 	This file controls the operating mode of hibernation (Suspend-to-Disk).
204 		Put the system into a special low-power state (e.g. ACPI S4) to
215 		Power off the system.
223 		If the system is successfully woken up from that state, discard
231 		just woken up from hibernation and the currently running kernel
232 		instance was a restore kernel and follow up with full system
241 	to :file:`/sys/power/state`.
248 	It can be written a string representing a non-negative integer that will
249 	be used as a best-effort upper limit of the image size, in bytes.  The
275 :ref:`suspend-to-idle <s2idle>` state.  The first one is to write "freeze"
276 directly to :file:`/sys/power/state`.  The second one is to write "s2idle" to
277 :file:`/sys/power/mem_sleep` and then to write "mem" to
278 :file:`/sys/power/state`.  Likewise, there are two ways to make the system go
282 system go into the :ref:`suspend-to-RAM <s2ram>` state (write "deep" into
283 :file:`/sys/power/mem_sleep` and "mem" into :file:`/sys/power/state`).
286 into :file:`/sys/power/mem_sleep`) is either "deep" (on the majority of systems
287 supporting :ref:`suspend-to-RAM <s2ram>`) or "s2idle", but it can be overridden
290 default may be "s2idle" even if :ref:`suspend-to-RAM <s2ram>` is supported in