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

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Date:	Wed, 5 May 2010 15:13:52 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Matthew Garrett <mjg@...hat.com>
cc:	Mark Brown <broonie@...nsource.wolfsonmicro.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>, <rebecca@...roid.com>
Subject: Re: [PATCH 0/8] Suspend block api (version 6)

On Wed, 5 May 2010, Matthew Garrett wrote:

> > Clearly if there's a call in progress you don't want to shut the codec
> > down.  Are there any other circumstances?  Would they vary according to
> > whether the suspend was forced or opportunistic?
> 
> Yeah, ok. We probably do need to figure this out.
> 
> (Cc:ing Rebecca to see how this got handled on Droid)
> 
> The current state of affairs is that a system suspend request is 
> expected to put the device in as low a power state as possible given the 
> required wakeup events. Runtime power management is expected to put the 
> device in as low a power state as possible given its usage constraints. 
> If opportunistic suspend does the former then it'll tear down devices 
> that may be in use, but we don't have any real way to indicate usage 
> constraints other than the phone app taking a wakelock - and that means 
> leaving userspace running during calls, which seems excessive.
> 
> Mark's right in that the only case I can think of that's really relevant 
> right now is the audio hardware, so the inelegant solution is that this 
> is something that could be provided at the audio level. Is this 
> something we want a generic solution for? If so, what should it look 
> like?

Should the audio driver be smart enough to know that the codec needs to
remain powered up during every opportunistic suspend?

Or only during opportunistic suspends while a call is in progress?  

Does it know when a call is in progress?

Does Android use forced suspends?

If it does, are they supposed to shut down the codec?

Alan Stern

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