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doc: pm: Update system device pm

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Add new information about new property to
enable/disable device power management per
power state.

Signed-off-by: Flavio Ceolin <flavio.ceolin@intel.com>
This commit is contained in:
Flavio Ceolin 2023-08-03 13:27:35 -07:00 • committed by Anas Nashif
commit dcf22a66de
1 changed files with 33 additions and 3 deletions
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36
doc/services/pm/device.rst
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@ -72,16 +72,46 @@ For more information, see :ref:`pm-device-runtime`.
System-Managed Device Power Management
======================================
The system managed device power management (PM) framework is a method where
devices are suspended along with the system entering a CPU (or SoC) power state.
It can be enabled by setting :kconfig:option:`CONFIG_PM_DEVICE_SYSTEM_MANAGED`.
When using this method, device power management is mostly done inside
:c:func:`pm_system_suspend()` along with entering a CPU or SOC power state.
:c:func:`pm_system_suspend()`.
If a decision to enter a CPU lower power state is made, the power management
subsystem will suspend devices before changing state. The subsystem takes care
of suspending devices following their initialization order, ensuring that
subsystem will check if the selected low power state triggers device power
management and then suspend devices before changing state. The subsystem takes
care of suspending devices following their initialization order, ensuring that
possible dependencies between them are satisfied. As soon as the CPU wakes up
from a sleep state, devices are resumed in the opposite order that they were
suspended.
The decision about suspending devices when entering a low power state is done based on the
state and if it has set the property ``zephyr,pm-device-disabled``. Here is
an example of a target with two low power states with only one triggering device power
management:
.. code-block:: devicetree
/* Node in a DTS file */
cpus {
power-states {
state0: state0 {
compatible = "zephyr,power-state";
power-state-name = "standby";
min-residency-us = <5000>;
exit-latency-us = <240>;
zephyr,pm-device-disabled;
};
state1: state1 {
compatible = "zephyr,power-state";
power-state-name = "suspend-to-ram";
min-residency-us = <8000>;
exit-latency-us = <360>;
};
};
};
.. note::
When using :ref:`pm-system`, device transitions can be run from the idle thread.