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authorRafael J. Wysocki <rjw@sisk.pl>2011-02-16 21:53:17 +0100
committerRafael J. Wysocki <rjw@sisk.pl>2011-03-15 00:43:16 +0100
commit7538e3db6e015e890825fbd9f8659952896ddd5b (patch)
tree01a6d8c97599474d9c5fc1ed0eb6f0addaec5652 /Documentation/power
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PM: Add support for device power domains
The platform bus type is often used to handle Systems-on-a-Chip (SoC) where all devices are represented by objects of type struct platform_device. In those cases the same "platform" device driver may be used with multiple different system configurations, but the actions needed to put the devices it handles into a low-power state and back into the full-power state may depend on the design of the given SoC. The driver, however, cannot possibly include all the information necessary for the power management of its device on all the systems it is used with. Moreover, the device hierarchy in its current form also is not suitable for representing this kind of information. The patch below attempts to address this problem by introducing objects of type struct dev_power_domain that can be used for representing power domains within a SoC. Every struct dev_power_domain object provides a sets of device power management callbacks that can be used to perform what's needed for device power management in addition to the operations carried out by the device's driver and subsystem. Namely, if a struct dev_power_domain object is pointed to by the pwr_domain field in a struct device, the callbacks provided by its ops member will be executed in addition to the corresponding callbacks provided by the device's subsystem and driver during all power transitions. Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl> Tested-and-acked-by: Kevin Hilman <khilman@ti.com>
Diffstat (limited to 'Documentation/power')
-rw-r--r--Documentation/power/devices.txt45
1 files changed, 44 insertions, 1 deletions
diff --git a/Documentation/power/devices.txt b/Documentation/power/devices.txt
index dd9b49251db..df1a5cb10c4 100644
--- a/Documentation/power/devices.txt
+++ b/Documentation/power/devices.txt
@@ -1,6 +1,6 @@
Device Power Management
-Copyright (c) 2010 Rafael J. Wysocki <rjw@sisk.pl>, Novell Inc.
+Copyright (c) 2010-2011 Rafael J. Wysocki <rjw@sisk.pl>, Novell Inc.
Copyright (c) 2010 Alan Stern <stern@rowland.harvard.edu>
@@ -507,6 +507,49 @@ routines. Nevertheless, different callback pointers are used in case there is a
situation where it actually matters.
+Device Power Domains
+--------------------
+Sometimes devices share reference clocks or other power resources. In those
+cases it generally is not possible to put devices into low-power states
+individually. Instead, a set of devices sharing a power resource can be put
+into a low-power state together at the same time by turning off the shared
+power resource. Of course, they also need to be put into the full-power state
+together, by turning the shared power resource on. A set of devices with this
+property is often referred to as a power domain.
+
+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.
+
+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.
+
+
System Devices
--------------
System devices (sysdevs) follow a slightly different API, which can be found in