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PM / Runtime: Document power.runtime_auto and related functions

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The power.runtime_auto device flag and the helper functions
pm_runtime_allow() and pm_runtime_forbid() used to modify it are a
part of the run-time power management framework and therefore they
should be described in Documentation/power/runtime_pm.txt.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
This commit is contained in:
Rafael J. Wysocki 2010-03-06 21:28:17 +01:00
parent 64096c1741
commit 87d1b3e60b
1 changed files with 28 additions and 0 deletions
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Documentation/power/runtime_pm.txt
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@ -224,6 +224,12 @@ defined in include/linux/pm.h:
RPM_SUSPENDED, which means that each device is initially regarded by the
PM core as 'suspended', regardless of its real hardware status
unsigned int runtime_auto;
- if set, indicates that the user space has allowed the device driver to
power manage the device at run time via the /sys/devices/.../power/control
interface; it may only be modified with the help of the pm_runtime_allow()
and pm_runtime_forbid() helper functions
All of the above fields are members of the 'power' member of 'struct device'.
4. Run-time PM Device Helper Functions
@ -329,6 +335,16 @@ drivers/base/power/runtime.c and include/linux/pm_runtime.h:
'power.runtime_error' is set or 'power.disable_depth' is greater than
zero)
void pm_runtime_allow(struct device *dev);
- set the power.runtime_auto flag for the device and decrease its usage
counter (used by the /sys/devices/.../power/control interface to
effectively allow the device to be power managed at run time)
void pm_runtime_forbid(struct device *dev);
- unset the power.runtime_auto flag for the device and increase its usage
counter (used by the /sys/devices/.../power/control interface to
effectively prevent the device from being power managed at run time)
It is safe to execute the following helper functions from interrupt context:
pm_request_idle()
@ -382,6 +398,18 @@ may be desirable to suspend the device as soon as ->probe() or ->remove() has
finished, so the PM core uses pm_runtime_idle_sync() to invoke the
subsystem-level idle callback for the device at that time.
The user space can effectively disallow the driver of the device to power manage
it at run time by changing the value of its /sys/devices/.../power/control
attribute to "on", which causes pm_runtime_forbid() to be called. In principle,
this mechanism may also be used by the driver to effectively turn off the
run-time power management of the device until the user space turns it on.
Namely, during the initialization the driver can make sure that the run-time PM
status of the device is 'active' and call pm_runtime_forbid(). It should be
noted, however, that if the user space has already intentionally changed the
value of /sys/devices/.../power/control to "auto" to allow the driver to power
manage the device at run time, the driver may confuse it by using
pm_runtime_forbid() this way.
6. Run-time PM and System Sleep
Run-time PM and system sleep (i.e., system suspend and hibernation, also known