linux-kernel - Re: [PATCH] PM: Make system-wide PM and runtime PM treat subsystems consistently

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Message-Id: <201102182114.25098.rjw@sisk.pl>
Date:	Fri, 18 Feb 2011 21:14:24 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Greg KH <greg@...ah.com>
Cc:	"R. J. Wysocki" <Rafal.Wysocki@....edu.pl>,
	Alan Stern <stern@...land.harvard.edu>,
	"Linux-pm mailing list" <linux-pm@...ts.linux-foundation.org>,
	Kevin Hilman <khilman@...com>,
	Grant Likely <grant.likely@...retlab.ca>,
	LKML <linux-kernel@...r.kernel.org>,
	Magnus Damm <magnus.damm@...il.com>,
	Len Brown <lenb@...nel.org>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Subject: Re: [PATCH] PM: Make system-wide PM and runtime PM treat subsystems consistently

On Friday, February 18, 2011, Greg KH wrote:
> On Fri, Feb 18, 2011 at 12:54:25AM +0100, R. J. Wysocki wrote:
> > 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 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@...k.pl>
> > Acked-by: Kevin Hilman <khilman@...com>
> > Reasoning-sounds-sane-to: Grant Likely <grant.likely@...retlab.ca>
> 
> Acked-by: Greg Kroah-Hartman <gregkh@...e.de>
> 
> You are going to take this through your tree, right?

Yes, I am.  Thanks!

Rafael
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