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

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Date:	Mon, 31 Jan 2011 15:43:41 -0800
From:	Kevin Hilman <khilman@...com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	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>,
	Alan Stern <stern@...land.harvard.edu>,
	Len Brown <lenb@...nel.org>
Subject: Re: [RFC][PATCH] Power domains for platform bus type

"Rafael J. Wysocki" <rjw@...k.pl> writes:

>> Also, what is the use case for having 2 sets of power_domain ops?  My
>> gut tells me that you'd only want to do post ops on the
>> {freeze,suspend,poweroff} path and pre ops on the {resume,thaw,restore}
>> path.  It seems overly engineered to me, but I may be missing
>> something fundamental.
>
> Well, that's a part of the RFC, actually. :-)
>
> For the subsystems I've worked with (PCI, ACPI, PNP to some extent) one set
> would be sufficient, but I don't know of every possible use case.

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.

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().

Kevin

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