Date:	Fri, 7 May 2010 05:37:21 -0700
From:	Brian Swetland <swetland@...gle.com>
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Cc:	Theodore Tso <tytso@....edu>,
	Arve Hjønnevåg <arve@...roid.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Matthew Garrett <mjg@...hat.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Kevin Hilman <khilman@...prootsystems.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 Fri, May 7, 2010 at 5:25 AM, Mark Brown
<broonie@...nsource.wolfsonmicro.com> wrote:
> On Fri, May 07, 2010 at 07:29:47AM -0400, Theodore Tso wrote:
>
>> This sounds like it may be something unique to your board/product.  Or
>> am I missing something?
>
> I suspect you're missing something here - I'm approaching this as one of
> the maintainers of the embedded audio subsystem for the kernel.  I need
> to worry about any system running Linux which has an embedded style
> audio subsystem.  The problem might be unique to audio, but I can't say
> that for certain.
>
>> One of the challenges with PM in the embedded world is that everybody
>> seems to have slightly different assumptions, and hardware that doesn't
>> behave the same way.
>
> This isn't really a problem for audio - we've already got a subsystem
> which copes well with pretty much all systems and does runtime PM that's
> equivalent to suspending already, which is half the problem here.  If we
> had less generalisation this would probably not have come up.
>
>> More than once this discussion has wandered off into the weeds wrt to
>> whether this patch series is ready to be merged, since there are so many
>> drivers blocked on it....
>
> Once more, my main objective here has been to make sure that when this
> is merged we've got a joined up story about how people think this hangs
> together, which I think we have now.  As I say now that we have that
> understanding I don't see any reason to block merge.
>
> It's unfortunate that I only noticed that this was actually wakelocks
> very late in the day but I think I can get an implementation which
> handles paths that ignore suspends done quickly.

Do you mean an implementation of embedded linux audio or an
implementation of suspend blockers "which handles paths that ignore
suspends"?  I assume you mean the former, but maybe I misunderstand.

We've done a lot of work around multicore SoCs where the baseband
generally owns a lot of the audio routing and so on, but we do as
general policy not disable audio, codecs, and amps while playback or
record is underway.  I suppose for environments more like a pc laptop
where the expectation is the world stops when you close the lid a
different policy would be preferable.

We typically fire up codecs and amps when playback starts (if they
were off), and usually set a timer for a couple seconds after playback
stops to spin them down (since you tend to have to delay while they're
powering up to avoid pops, etc, and if the system just played a short
sound there's a reasonable chance it'll follow that with another).

Apologies about the name confusion -- last year when we first started
pushing these patches out there was much dislike for the name wakelock
and after a lot of back and forth suspend_block ended up as the least
hated of the suggested alternatives (I kinda like "wakelock" as a
name, but maybe that's just brain rot after dealing with 'em for four
years now).

Brian
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