linux-kernel - Re: [alsa-devel] [PATCH] ASoC: generic: add generic compound card with DT support

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Date:	Thu, 2 Jan 2014 18:35:53 +0000
From:	Mark Brown <broonie@...nel.org>
To:	Jean-Francois Moine <moinejf@...e.fr>
Cc:	Lars-Peter Clausen <lars@...afoo.de>,
	Liam Girdwood <lgirdwood@...il.com>,
	alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org
Subject: Re: [alsa-devel] [PATCH] ASoC: generic: add generic compound card
 with DT support

On Thu, Jan 02, 2014 at 06:50:55PM +0100, Jean-Francois Moine wrote:

> No, the 'endpoint' <=> 'remote-endpoint' is a point to point relation.
> Even if the sources and sinks are not explicitly defined, the way
> the stream flows is easy to find: the main source is always in the
> 'audio-controller' node

But the links in question aren't point to point links and may be
bidirectional...

> Usually, the devices don't have to know to which other device they are
> connected, and, yes, the reverse pointer sink to source is not useful.

This may be the case for the systems you've looked at but other designs
are quite common.

> But the way (link) the audio stream comes from may be important to
> know. This is the case for the HDMI CODEC which must tell the HDMI
> transmitter from which hardware port(s) ('reg') it may get the audio
> stream. That's why, the HDMI encoder has two endpoints in its audio
> port, each endpoint being a different CODEC DAI.

Obviously if there are multiple DAIs on a device then it needs to be
possible to represent them separately but that seems orthogonal to the
rest of the discussion (and resolved already)?

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