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

From: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
To: Mark Brown <broonie@kernel.org>, Vinod Koul <vinod.koul@intel.com>
Cc: alsa-devel@alsa-project.org, Lars-Peter Clausen <lars@metafoo.de>,
	misael.lopez@ti.com, Benoit Cousson <bcousson@baylibre.com>,
	lgirdwood@gmail.com
Subject: Re: [PATCH v4 6/8] ASoC: compress: Add support for DAI multicodec
Date: Thu, 03 Jul 2014 14:09:11 -0500	[thread overview]
Message-ID: <53B5AA57.5060804@linux.intel.com> (raw)
In-Reply-To: <20140703183804.GO410@sirena.org.uk>

>>> 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.
>
> They're having the SoC play stereo (or whatever) data and then having
> multiple CODECs on the bus, each parsing some subset of the channels
> (typically one channel per CODEC).

This sort of stream aggregation/split is a very valid use case that's 
coming to mobiles in the very near future with new interfaces being 
standardized.

>
>> So how can we have a situation where we have compressed device linked to
>> multiple codecs?
>
> If it's intended to be DPCM only (which it iss now I think about it) it
> sounds like you can't have it linked to *any* real CODECS, at least not
> directly!

there are very few references to codec_dais in soc-compress and some are 
in sections copy/pasted from soc-pcm, which makes me wonder as well if 
they needed to be there in the first place.
-Pierre