linux-kernel - Re: [RFC][PATCH 2/2] PM: Make system-wide PM and runtime PM handle subsystems consistently

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Date:	Tue, 15 Feb 2011 12:48:24 -0700
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Kevin Hilman <khilman@...com>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux-pm mailing list <linux-pm@...ts.linux-foundation.org>,
	Greg KH <greg@...ah.com>, LKML <linux-kernel@...r.kernel.org>,
	Magnus Damm <magnus.damm@...il.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Len Brown <lenb@...nel.org>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Subject: Re: [RFC][PATCH 2/2] PM: Make system-wide PM and runtime PM handle
 subsystems consistently

On Tue, Feb 15, 2011 at 10:10:06AM -0800, Kevin Hilman wrote:
> "Rafael J. Wysocki" <rjw@...k.pl> writes:
> 
> > From: Rafael J. Wysocki <rjw@...k.pl>
> >
> > 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, while the device
> > type callback will be executed during runtime resume).
> >
> > Make all of the power management code treat subsystem callbacks in
> > a consistent way, such that:
> > (1) If the device's bus type is defined (eg. dev->bus is not NULL)
> >     and its pm pointer is not NULL, the callbacks from dev->bus->pm
> >     will be used.
> > (2) If dev->bus is NULL or dev->bus->pm is NULL, but the device's
> >     device 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.
> > (3) If dev->bus is NULL or dev->bus->pm is NULL and dev->type is
> >     NULL or dev->type->pm is NULL, the callbacks from dev->class->pm
> >     will be used provided that both dev->class and dev->class->pm
> >     are not NULL.
> >
> > Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
> 
> This looks good,  consistency between system and runtime PM is a great
> help to readability.
> 
> Acked-by: Kevin Hilman <khilman@...com>

Reasoning-sounds-sane-to: Grant Likely <grant.likely@...retlab.ca>

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