admin-guide/pm/suspend-flows.rst

1 .. SPDX-License-Identifier: GPL-2.0
12 At least one global system-wide transition needs to be carried out for the
13 system to get from the working state into one of the supported
14 :doc:`sleep states <sleep-states>`.  Hibernation requires more than one
16 referred to as *system-wide suspend* (or simply *system suspend*) states, need
19 For those sleep states, the transition from the working state of the system into
20 the target sleep state is referred to as *system suspend* too (in the majority
21 of cases, whether this means a transition or a sleep state of the system should
22 be clear from the context) and the transition back from the sleep state into the
23 working state is referred to as *system resume*.
27 significant differences between the :ref:`suspend-to-idle <s2idle>` code flows
28 and the code flows related to the :ref:`suspend-to-RAM <s2ram>` and
31 The :ref:`suspend-to-RAM <s2ram>` and :ref:`standby <standby>` sleep states
33 boils down to the platform-specific actions carried out by the suspend and
37 *platform-dependent suspend* states in what follows.
42 Suspend-to-idle Suspend Code Flow
46 state to the :ref:`suspend-to-idle <s2idle>` sleep state:
48  1. Invoking system-wide suspend notifiers.
53     That allows them to prepare for the change of the system state and to clean
54     up after getting back to the working state.
87     phase and high-level ("action") interrupt handlers are prevented from being
91     interrupt controllers without performing any device-specific actions that
92     would be triggered in the working state of the system (those actions are
101     When all devices have been suspended, CPUs enter the idle loop and are put
102     into the deepest available idle state.  While doing that, each of them
106     The last CPU to enter the idle state also stops the timekeeping which
109     That allows the CPUs to stay in the deep idle state relatively long in one
112     From this point on, the CPUs can only be woken up by non-timer hardware
113     interrupts.  If that happens, they go back to the idle state unless the
120 Suspend-to-idle Resume Code Flow
124 :ref:`suspend-to-idle <s2idle>` sleep state into the working state:
128     When one of the CPUs is woken up (by a non-timer hardware interrupt), it
129     leaves the idle state entered in the last step of the preceding suspend
137  2. Resuming devices and restoring the working-state configuration of IRQs.
146     The working-state configuration of IRQs is restored after the *noirq* resume
147     phase and the runtime PM API is re-enabled for every device whose driver
157  4. Invoking system-wide resume notifiers.
164 Platform-dependent Suspend Code Flow
168 state to platform-dependent suspend state:
170  1. Invoking system-wide suspend notifiers.
172     This step is the same as step 1 of the suspend-to-idle suspend transition
177     This step is the same as step 2 of the suspend-to-idle suspend transition
182     This step is analogous to step 3 of the suspend-to-idle suspend transition
186     There are platforms that can go into a very deep low-power state internally
187     when all CPUs in them are in sufficiently deep idle states and all I/O
188     devices have been put into low-power states.  On those platforms,
189     suspend-to-idle can reduce system power very effectively.
191     On the other platforms, however, low-level components (like interrupt
192     controllers) need to be turned off in a platform-specific way (implemented
196     That usually prevents in-band hardware interrupts from waking up the system,
197     which must be done in a special platform-dependent way.  Then, the
202  4. Disabling non-boot CPUs.
204     On some platforms the suspend hooks mentioned above must run in a one-CPU
212     offline (typically, the CPUs that have been taken offline go into deep idle
223  6. Platform-specific power removal.
233 Platform-dependent Resume Code Flow
237 platform-dependent suspend state into the working state:
239  1. Platform-specific system wakeup.
242     wakeup devices (which need not be an in-band hardware interrupt)  and
249     The suspend-time configuration of the core system components is restored and
252  3. Re-enabling non-boot CPUs.
255     back online and their suspend-time configuration is restored.
257  4. Resuming devices and restoring the working-state configuration of IRQs.
259     This step is the same as step 2 of the suspend-to-idle suspend transition
264     This step is the same as step 3 of the suspend-to-idle suspend transition
267  6. Invoking system-wide resume notifiers.
269     This step is the same as step 4 of the suspend-to-idle suspend transition