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
14 :doc:`sleep states <sleep-states>`.  Hibernation requires more than one
16 referred to as *system-wide suspend* (or simply *system suspend*) states, need
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.
54     up after getting back to the working state.
60     it and to prevent user space from entering the kernel while the next step
87     phase and high-level ("action") interrupt handlers are prevented from being
91     interrupt controllers without performing any device-specific actions that
104     the tick do not occur until the CPU is woken up by another interrupt source.
108     forward until the first CPU that is woken up restarts the timekeeping.
112     From this point on, the CPUs can only be woken up by non-timer hardware
114     interrupt that woke up one of them comes from an IRQ that has been armed for
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
131     by another CPU that woke up earlier) and the scheduler tick on that CPU is
134     If the interrupt that has woken up the CPU was armed for system wakeup,
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
152     Tasks frozen in step 2 of the preceding `suspend <s2idle_suspend_>`_
153     transition are "thawed", which means that they are woken up from the
157  4. Invoking system-wide resume notifiers.
159     This is analogous to step 1 of the `suspend <s2idle_suspend_>`_ transition
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
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
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.
241     The platform is woken up by a signal from one of the designated system
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.
254     The CPUs disabled in step 4 of the preceding suspend transition are taken
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