linux-kernel - Re: [PATCH 0/8] Suspend block api (version 6)

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Date:	Wed, 5 May 2010 15:20:40 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
cc:	Matthew Garrett <mjg@...hat.com>,
	Brian Swetland <swetland@...gle.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Kevin Hilman <khilman@...prootsystems.com>,
	Arve Hjønnevåg <arve@...roid.com>,
	<linux-pm@...ts.linux-foundation.org>,
	<linux-kernel@...r.kernel.org>, Tejun Heo <tj@...nel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Paul Walmsley <paul@...an.com>, <magnus.damm@...il.com>,
	mark gross <mgross@...ux.intel.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Geoff Smith <geoffx.smith@...el.com>
Subject: Re: [PATCH 0/8] Suspend block api (version 6)

On Wed, 5 May 2010, Mark Brown wrote:

> > In short, I'm trying to get at how much information drivers _really_ 
> > need to have about the reason for a system suspend.
> 
> It's not exactly the *reason* that makes the difference, it's more that
> this aggressive use of suspend makes much more apparent a problem which
> might exist anyway for this sort of hardware.

Then the underlying problem should be solved -- hopefully in a nice, 
system-independent way.  But I'm still trying to understand exactly 
what that underlying problem _is_.

That means understanding when the codec needs to be shut down and when
it doesn't, and knowing how much of this information is available to
the driver.

> When we get runtime PM delviering similar power levels we'll sidestep
> the problem since we won't need to do a system wide suspend.

One the face of it, a runtime-PM solution would dictate that the
codec's driver ought to turn off the codec whenever the driver thinks
it isn't being used.  Ergo, if the driver didn't know when a call was
in progress, it would use runtime PM to turn off the codec during a
call.

For this reason I don't see how using runtime PM instead of suspend
blockers would solve anything.

Alan Stern

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