linux-kernel - Re: [RFC][PATCH] PM: Make power domain callbacks take precedence over subsystem ones

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Date:	Sat, 16 Apr 2011 10:17:51 -0700
From:	Kevin Hilman <khilman@...com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Linux PM mailing list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Len Brown <lenb@...nel.org>, linux-sh@...r.kernel.org,
	lethal@...ux-sh.org, Magnus Damm <magnus.damm@...il.com>,
	Alan Stern <stern@...land.harvard.edu>
Subject: Re: [RFC][PATCH] PM: Make power domain callbacks take precedence
 over subsystem ones

On Wed, 2011-04-13 at 02:05 +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rjw@...k.pl>
> 
> Change the PM core's behavior related to power domains in such a way
> that, if a power domain is defined for a given device, its callbacks
> will be executed instead of and not in addition to the device
> subsystem's PM callbacks.
> 
> The idea behind the initial implementation of power domains handling
> by the PM core was that power domain callbacks would be executed in
> addition to subsystem callbacks, so that it would be possible to
> extend the subsystem callbacks by using power domains.  It turns out,
> however, that this wouldn't be really convenient in some important
> situations.
> 
> For example, there are systems in which power can only be removed
> from entire power domains.  On those systems it is not desirable to
> execute device drivers' PM callbacks until it is known that power is
> going to be removed from the devices in question, which means that
> they should be executed by power domain callbacks rather then by
> subsystem (e.g. bus type) PM callbacks, because subsystems generally
> have no information about what devices belong to which power domain.
> Thus, for instance, if the bus type in question is the platform bus
> type, its PM callbacks generally should not be called in addition to
> power domain callbacks, because they run device drivers' callbacks
> unconditionally if defined.
> 
> While in principle the default subsystem PM callbacks, or a subset of
> them, may be replaced with different functions, it doesn't seem
> correct to do so, because that would change the subsystem's behavior
> with respect to all devices in the system, regardless of whether or
> not they belong to any power domains.  Thus, the only remaining
> option is to make power domain callbacks take precedence over
> subsystem callbacks.
> 
> Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>

Leaving the issue of to (re)name this field aside:

Acked-by: Kevin Hilman <khilman@...com>


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