Re: [PATCH v4 6/8] ASoC: compress: Add support for DAI multicodec

From: Vinod Koul <vinod.koul@intel.com>
To: Mark Brown <broonie@kernel.org>
Cc: alsa-devel@alsa-project.org, misael.lopez@ti.com,
	Lars-Peter Clausen <lars@metafoo.de>,
	lgirdwood@gmail.com, Benoit Cousson <bcousson@baylibre.com>
Subject: Re: [PATCH v4 6/8] ASoC: compress: Add support for DAI multicodec
Date: Thu, 3 Jul 2014 21:45:17 +0530	[thread overview]
Message-ID: <20140703161517.GQ2296@intel.com> (raw)
In-Reply-To: <20140703121846.GB410@sirena.org.uk>

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On Thu, Jul 03, 2014 at 01:18:46PM +0100, Mark Brown wrote:
> > BUT Now thinking over this again, does this make sense do do with multiple
> > codecs??
> 
> > For folks haveing decoders in DSP inside SoC, the compressed device will be
> > actually a FE. The BE will be PCM to which codec would be linked. The folks
> > supporting decoders inside codec like WM wont ever need this.
> 
> > Mark, do you agree to this?
> 
> > So re-thinking again on why we need this??
> 
> The use case tends to be for applications that have one device per
> physical output.  This isn't normally mobile, it's normally high
> performance audio applications where people are doing things to try to
> electrically isolate the analogue outputs or dealing with high power so
> need to keep speaker outputs physically separate.  I can imagine set top
> box type applications (which do use offloaded media decode) doing this.

Not sure if I follow you, I have no idea of how these systems work.

But if sound card has compressed device it would need to represent using DPCM as
we don't know the decoder PCM output. The multiple codecs would then connect to
the PCM BE. 
So on Compressed FE, we wont have multiple codecs.

For codecs, the compressed audio will go to one codec, multiple ones wont make
sense.

So how can we have a situation where we have compressed device linked to
multiple codecs?

-- 
~Vinod

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