Re: [RFC][PATCH 1/2] PM: Add support for device power domains

On Monday, February 14, 2011, Alan Stern wrote:

On Sat, 12 Feb 2011, Rafael J. Wysocki wrote:

quoted

From: Rafael J. Wysocki <redacted>

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.

Overall this looks very good.

quoted

Index: linux-2.6/include/linux/pm.h
===================================================================

--- linux-2.6.orig/include/linux/pm.h
+++ linux-2.6/include/linux/pm.h

@@ -463,6 +463,14 @@ struct dev_pm_info {
 
 extern void update_pm_runtime_accounting(struct device *dev);
 
+/*
+ * Power domains provide callbacks that are executed during system suspend,
+ * hibernation, system resume and during runtime PM transitions along with
+ * subsystem-level and driver-level callbacks.
+ */
+struct dev_power_domain {
+	struct dev_pm_ops	ops;
+};

I don't have a clear picture of how people are going to want to use 
these dev_power_domain structures.  Should there be a

	void			*priv;

member as well?

Well, I'm not sure.  What would be the purpose of it?

Rafael