linux-kernel - Re: driver power operations (was Re: suspend2 merge)

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Date:	Fri, 27 Apr 2007 14:40:29 +0200
From:	Pavel Machek <pavel@....cz>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Johannes Berg <johannes@...solutions.net>,
	Nick Piggin <npiggin@...e.de>, Mike Galbraith <efault@....de>,
	linux-kernel@...r.kernel.org, Adrian Bunk <bunk@...sta.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Con Kolivas <kernel@...ivas.org>,
	suspend2-devel@...ts.suspend2.net, Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	linux-pm <linux-pm@...ts.linux-foundation.org>
Subject: Re: driver power operations (was Re: suspend2 merge)

Hi!

> > And, incidentally, it could possibly make both suspend and hibernate
> > work much faster too. The comments there talk about "minimally power
> > management aware" drivers which always do the wrong thing for suspend,
> > in that they always reset everything... Of course, some drivers will
> > actually need to do that, but if freeze/suspend and thaw/restart/resume
> > have the same prototypes (probably just int <function>(void)) then
> > drivers can trivially assign the same there.
> > And hibernate would benefit since a lot of drivers could do a lot less
> > work for freeze/thaw.
> 
> I violently agree with all of the above.
> 
> Moreover, for the hibernation we have two special cases that are of no interest
> for the suspend:
> 1) drivers compiled as modules and not loaded before we restore the image
> 2) drivers that need to allocate much memory in .freeze()
> 
> > Or, if we don't want to have five calls and use 40 bytes (on 64-bit)
> > just for these callback pointers for each device we could just as well
> > have a single callback ->pm(what) and make "what" indicate which one of
> > these five things... But then drivers can't make that code depend on the
> > swsusp configuration which would be doable with five callbacks.
> 
> Five callbacks are fine by me, especially if we can define reasonable defaults
> for the hibernation (and can we?).

Well, we still can default to suspend(PMSG_FREEZE) for freeze(), and
resume() for thaw(). Anything else is just not sane way forward.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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