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

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Date:	Tue, 04 May 2010 16:14:40 -0700
From:	Kevin Hilman <khilman@...prootsystems.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Mark Brown <broonie@...nsource.wolfsonmicro.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)

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

> 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.

Sure, but there are driver authors and subsystem maintainers who care
about optimal PM in "normal" Linux *and* in Android.

As a PM maintainer for an embedded platform (OMAP) used in both, I
certainly care about both, so "disable it if you don't like it" is not
really an option.

IMO, driver/subsystem authors should not have to care if the userspace
is Android or not.  We should be working towards a world where Android
is not a special case.

Kevin
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