linux-kernel - Re: [RFC][PATCH] Power domains for platform bus type

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Date:	Mon, 31 Jan 2011 22:40:44 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Kevin Hilman <khilman@...com>
cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Grant Likely <grant.likely@...retlab.ca>,
	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>,
	Len Brown <lenb@...nel.org>
Subject: Re: [RFC][PATCH] Power domains for platform bus type

On Mon, 31 Jan 2011, Kevin Hilman wrote:

> For the on-chip SoC devices we're managing with OMAP, we're currently
> only using one set: post ops on [runtime_]suspend and pre ops on
> [runtime_]resume.
> 
> However, I could imagine (at least conceptually) using the pre ops on
> suspend to do some constraints checking and/or possibly some
> management/notification of dependent devices.  Another possiblity
> (although possibly racy) would be using the pre ops on suspend to
> initiate some high-latency operations.

Dependency management is very relevant here, since we're talking about
relations that explicitly aren't of the parent-child type.  If any of
the devices in question get marked for async suspend/resume, for
example, they certainly will need dependency handling.

> I guess the main problem with two sets is wasted space.  e.g, if I move
> OMAP to this (already hacking on it) there will be only 2 functions used
> in post ops: [runtime_]suspend() and 2 used in pre ops [runtime_]_resume().

The wasted space is minimal; we're only talking about one extra pm_ops
structure for each power domain.  Presumably any reasonable SoC isn't
going to have a tremendous number of separate power domains.  Or am I
wrong about this?

Alan Stern

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