admin-guide/pm/sleep-states.rst

1 .. SPDX-License-Identifier: GPL-2.0
5 System Sleep States
13 Sleep states are global low-power states of the entire system in which user
18 Sleep States That Can Be Supported
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
43 or :ref:`suspend-to-RAM <s2ram>`, or it can be used in addition to any of the
50 -------
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
65 reduced relative to :ref:`suspend-to-idle <s2idle>` and it may be necessary to
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
93 On ACPI-based systems S2RAM requires some minimal boot-strapping code in the
98 relative to :ref:`suspend-to-idle <s2idle>` and :ref:`standby <standby>` and it
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
129 special low-power state (like ACPI S4), or it may simply power down itself.
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.
157 interface for system sleep regardless of the underlying system architecture or
163 	This file contains a list of strings representing sleep states supported
165 	to start a transition of the system into the sleep state represented by
169 	:ref:`hibernation <hibernation>`, :ref:`suspend-to-idle <s2idle>` and
170 	:ref:`standby <standby>` sleep states, respectively.  The "mem" string
174 	If the kernel does not support any system sleep states, this file is
183 	and "deep".  The "s2idle" string always represents :ref:`suspend-to-idle
184 	<s2idle>` and, by convention, "shallow" and "deep" represent
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
210 		mechanism to put the system to sleep after creating a
221 		Hybrid system suspend.  Put the system into the suspend sleep
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"
282 system go into the :ref:`suspend-to-RAM <s2ram>` state (write "deep" into
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