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docs: pm: Fix device busy information

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Remove invalid information about device busy API.

Signed-off-by: Flavio Ceolin <flavio.ceolin@intel.com>
This commit is contained in:
Flavio Ceolin 2021-05-10 23:25:50 -07:00 • committed by Anas Nashif
commit 7f667680f4
1 changed files with 5 additions and 16 deletions
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21
doc/reference/power_management/index.rst
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@ -327,22 +327,9 @@ off, then such transactions would be left in an inconsistent state. This
infrastructure guards such transactions by indicating to the SOC interface that
the device is in the middle of a hardware transaction.
When the :code:`pm_system_suspend()` is called, the SOC interface checks if any device
is busy. The SOC interface can then decide to execute a power management scheme other than deep sleep or
to defer power management operations until the next call of
:code:`pm_system_suspend()`.
An alternative to using the busy status mechanism is to use the
`distributed method`_ of device power management. In such a method where the
device power management is handled in a distributed manner rather than centrally in
:code:`pm_system_suspend()`, the decision to enter deep sleep can be made based
on whether all devices are already turned off.
This feature can be also used to emulate a hardware feature found in some SOCs
that causes the system to automatically enter deep sleep when all devices are idle.
In such an usage, the busy status can be set by default and cleared as each
device becomes idle. When :code:`pm_system_suspend()` is called, deep sleep can
be entered if no device is found to be busy.
When the :c:func:`pm_system_suspend()` is called, depending on the power state
returned by the policy manager, the system may suspend or put devices in low
power if they are not marked as busy.
Here are the APIs used to set, clear, and check the busy status of devices.
@ -377,6 +364,8 @@ Check Busy Status of Single Device API
Checks whether a device is busy. The API returns 0 if the device
is not busy.
This API is used by the system power management.
Check Busy Status of All Devices API
------------------------------------