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

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Date:	Sun, 17 Apr 2011 01:12:08 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Kevin Hilman <khilman@...com>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Magnus Damm <magnus.damm@...il.com>,
	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
Subject: Re: [RFC][PATCH] PM: Make power domain callbacks take precedence over subsystem ones

On Saturday, April 16, 2011, Kevin Hilman wrote:
> On Sat, 2011-04-16 at 01:18 +0200, Rafael J. Wysocki wrote:
> > On Friday, April 15, 2011, Alan Stern wrote:
> > > On Fri, 15 Apr 2011, Rafael J. Wysocki wrote:
> > > 
> > > > On Thursday, April 14, 2011, Magnus Damm wrote:
> > > 
> > > > > My only thought on this is if we really want to limit ourselves to
> > > > > only control power domains using these callbacks. I can imagine that
> > > > > some SoCs want to do other non-power domain specific operations with
> > > > > these callbacks, and if so, perhaps using the term power domain as
> > > > > name of the pointer in struct device would be somewhat odd. OTOH, I
> > > > > really dislike naming discussions in general and I can't really think
> > > > > of any good names. So it all looks more like a set of system specific
> > > > > PM override hooks.
> > > > > 
> > > > > Or is there something that is really power domain specific with these hooks?
> > > > 
> > > > Not in principle, but I think there is.  Namely, if there are two groups
> > > > of devices belonging to the same bus type (e.g. platform) that each require
> > > > different PM handling, it is legitimate to call them "power domains" (where
> > > > "domain" means "a set of devices related to each other because of the way
> > > > they need to be handled"), even if they don't share power resources.
> > > > 
> > > > Of course, if they do share power resources, the term is just right. :-)
> > > 
> > > They could be called "PM domains" instead of "power domains".  That's 
> > > legitimate because they do get used by the PM core, even if they don't 
> > > literally involve groups of devices sharing the same power supply.
> > 
> > Well, "power domain" can be regarded as a short form of "power management
> > domain", which makes the point kind of moot. ;-)
> 
> Except that on most embedded SoCs, the term power domain has specific
> meaning in hardware, so using something other than that is preferred
> IMO.
> 
> What this really is is just per-device dev_pm_ops, which platform code
> can use to group devices however it likes.
> 
> So rather than call it a power domain, or a PM domain, we could also
> just add a struct dev_pm_ops to struct device. 

Well, right.  But in the future this thing will be necessary to provide
additional information to _real_ power domain PM callbacks.  So it will
be more than just struct dev_pm_ops.

Thanks,
Rafael
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