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PM / Domains: Update documentation 

Commit 4d27e9dcff (PM: Make power
domain callbacks take precedence over subsystem ones) forgot to
update the device power management documentation to take changes
made by it into account.  Correct that mistake.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
This commit is contained in:
Rafael J. Wysocki 2011-06-21 23:25:32 +02:00
parent 4d1518f566
commit ca9c6890b5
1 changed files with 13 additions and 26 deletions
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39
Documentation/power/devices.txt
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@ -520,33 +520,20 @@ Support for power domains is provided through the pwr_domain field of struct
device. This field is a pointer to an object of type struct dev_power_domain,
defined in include/linux/pm.h, providing a set of power management callbacks
analogous to the subsystem-level and device driver callbacks that are executed
for the given device during all power transitions, in addition to the respective
subsystem-level callbacks. Specifically, the power domain "suspend" callbacks
(i.e. ->runtime_suspend(), ->suspend(), ->freeze(), ->poweroff(), etc.) are
executed after the analogous subsystem-level callbacks, while the power domain
"resume" callbacks (i.e. ->runtime_resume(), ->resume(), ->thaw(), ->restore,
etc.) are executed before the analogous subsystem-level callbacks. Error codes
returned by the "suspend" and "resume" power domain callbacks are ignored.
for the given device during all power transitions, instead of the respective
subsystem-level callbacks. Specifically, if a device's pm_domain pointer is
not NULL, the ->suspend() callback from the object pointed to by it will be
executed instead of its subsystem's (e.g. bus type's) ->suspend() callback and
anlogously for all of the remaining callbacks. In other words, power management
domain callbacks, if defined for the given device, always take precedence over
the callbacks provided by the device's subsystem (e.g. bus type).
Power domain ->runtime_idle() callback is executed before the subsystem-level
->runtime_idle() callback and the result returned by it is not ignored. Namely,
if it returns error code, the subsystem-level ->runtime_idle() callback will not
be called and the helper function rpm_idle() executing it will return error
code. This mechanism is intended to help platforms where saving device state
is a time consuming operation and should only be carried out if all devices
in the power domain are idle, before turning off the shared power resource(s).
Namely, the power domain ->runtime_idle() callback may return error code until
the pm_runtime_idle() helper (or its asychronous version) has been called for
all devices in the power domain (it is recommended that the returned error code
be -EBUSY in those cases), preventing the subsystem-level ->runtime_idle()
callback from being run prematurely.
The support for device power domains is only relevant to platforms needing to
use the same subsystem-level (e.g. platform bus type) and device driver power
management callbacks in many different power domain configurations and wanting
to avoid incorporating the support for power domains into the subsystem-level
callbacks. The other platforms need not implement it or take it into account
in any way.
The support for device power management domains is only relevant to platforms
needing to use the same device driver power management callbacks in many
different power domain configurations and wanting to avoid incorporating the
support for power domains into subsystem-level callbacks, for example by
modifying the platform bus type. Other platforms need not implement it or take
it into account in any way.
Device Low Power (suspend) States