PM: Make system-wide PM and runtime PM treat subsystems consistently

The code handling system-wide power transitions (eg. suspend-to-RAM)
can in theory execute callbacks provided by the device's bus type,
device type and class in each phase of the power transition.  In
turn, the runtime PM core code only calls one of those callbacks at
a time, preferring bus type callbacks to device type or class
callbacks and device type callbacks to class callbacks.

It seems reasonable to make them both behave in the same way in that
respect.  Moreover, even though a device may belong to two subsystems
(eg. bus type and device class) simultaneously, in practice power
management callbacks for system-wide power transitions are always
provided by only one of them (ie. if the bus type callbacks are
defined, the device class ones are not and vice versa).  Thus it is
possible to modify the code handling system-wide power transitions
so that it follows the core runtime PM code (ie. treats the
subsystem callbacks as mutually exclusive).

On the other hand, the core runtime PM code will choose to execute,
for example, a runtime suspend callback provided by the device type
even if the bus type's struct dev_pm_ops object exists, but the
runtime_suspend pointer in it happens to be NULL.  This is confusing,
because it may lead to the execution of callbacks from different
subsystems during different operations (eg. the bus type suspend
callback may be executed during runtime suspend of the device, while
the device type callback will be executed during system suspend).

Make all of the power management code treat subsystem callbacks in
a consistent way, such that:
(1) If the device's type is defined (eg. dev->type is not NULL)
    and its pm pointer is not NULL, the callbacks from dev->type->pm
    will be used.
(2) If dev->type is NULL or dev->type->pm is NULL, but the device's
    class is defined (eg. dev->class is not NULL) and its pm pointer
    is not NULL, the callbacks from dev->class->pm will be used.
(3) If dev->type is NULL or dev->type->pm is NULL and dev->class is
    NULL or dev->class->pm is NULL, the callbacks from dev->bus->pm
    will be used provided that both dev->bus and dev->bus->pm are
    not NULL.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Kevin Hilman <khilman@ti.com>
Reasoning-sounds-sane-to: Grant Likely <grant.likely@secretlab.ca>
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 7 insertions, 6 deletions

diff --git a/Documentation/power/runtime_pm.txt b/Documentation/power/runtime_pm.txt
index ffe55ffa540..654097b130b 100644
--- a/Documentation/power/runtime_pm.txt
+++ b/Documentation/power/runtime_pm.txt
@@ -1,6 +1,6 @@
 Run-time Power Management Framework for I/O Devices
 
-(C) 2009 Rafael J. Wysocki <rjw@sisk.pl>, Novell Inc.
+(C) 2009-2011 Rafael J. Wysocki <rjw@sisk.pl>, Novell Inc.
 (C) 2010 Alan Stern <stern@rowland.harvard.edu>
 
 1. Introduction
@@ -44,11 +44,12 @@ struct dev_pm_ops {
 };
 
 The ->runtime_suspend(), ->runtime_resume() and ->runtime_idle() callbacks are
-executed by the PM core for either the bus type, or device type (if the bus
-type's callback is not defined), or device class (if the bus type's and device
-type's callbacks are not defined) of given device.  The bus type, device type
-and device class callbacks are referred to as subsystem-level callbacks in what
-follows.
+executed by the PM core for either the device type, or the class (if the device
+type's struct dev_pm_ops object does not exist), or the bus type (if the
+device type's and class' struct dev_pm_ops objects do not exist) of the given
+device (this allows device types to override callbacks provided by bus types or
+classes if necessary).  The bus type, device type and class callbacks are
+referred to as subsystem-level callbacks in what follows.
 
 By default, the callbacks are always invoked in process context with interrupts
 enabled.  However, subsystems can use the pm_runtime_irq_safe() helper function