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

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Message-Id: <201005042237.56844.rjw@sisk.pl>
Date:	Tue, 4 May 2010 22:37:56 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Cc:	Kevin Hilman <khilman@...prootsystems.com>,
	Brian Swetland <swetland@...gle.com>,
	Arve Hjønnevåg <arve@...roid.com>,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	Alan Stern <stern@...land.harvard.edu>,
	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 Tuesday 04 May 2010, Mark Brown wrote:
> On Tue, May 04, 2010 at 11:06:39AM -0700, Kevin Hilman wrote:
> 
> > With opportunistic suspend, all of this flexibility is gone, and the
> > device/subsystem is told to go into the lowest power, highest latency
> > state, period.
> 
> Well, half the problem I have is that unfortunately it's not a case of
> doing that period.  The prime example I'm familiar with is that for
> understandable reasons users become irate when you power down the audio
> CODEC while they're in the middle of a call so if opportunistic PM is in
> use then the audio subsystem needs some additional help interpreting a
> suspend request so that it can figure out how to handle it.  Similar
> issues apply to PMICs, though less pressingly for various reasons.
> 
> Just to be clear, I do understand and mostly agree with the idea that
> opportunistic suspend presents a reasonable workaround for our current
> inability to deliver good power savings with runtime PM methods on many
> important platforms but I do think that if we're going to make this
> standard Linux PM functionality then we need to be clearer about how
> everything is intended to hang together.

At the moment the rule of thumb is: if you don't need the opportunistic
suspend, don't use it.  It is not going to be enabled by default on anything
other than Android right now.

However, since Android is a legitimate user of the Linux kernel, I see no
reason to reject this feature right away.  There are many kernel features
that aren't used by all platforms.

Rafael
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