[alsa-devel] Connecting two Codecs to the same CPU DAI

Mark Brown broonie at kernel.org
Tue Jul 16 19:47:03 CEST 2013

On Tue, Jul 16, 2013 at 07:07:33PM +0200, Daniel Mack wrote:
> On 16.07.2013 18:57, Mark Brown wrote:

> >>> No, no feature here.  Off the top of my head I'd suggest soc-pcm plus a
> >>> virtual DAI for the second link.

> >> That would still require userspace to open and configure both
> >> subdevices, right?

> > Shouldn't.

> How so? As each link exposes its own PCM subdevice, how would codec of
> link #1 get a hw_params call if an application just opens PCM subdevice
> #0 for playback? This is the case I want to address.

Half the point of soc-pcm is to decouple the streams seen by the
application layer from the DAIs that the driver sees so I'd expect us to
be able to map a single application layer/memory stream onto multiple
CODEC DAIs.  One front end connected to two back ends.

> > In principal yet but we want better DAPM integration I think - having an
> > unused device on the link probably ought not have any impact on other
> > devices for example.

> Well, if a link references two codecs, then both would be used in
> parallel, and none of it is unused. But maybe I don't get your point :)

If one of them has no active outputs or inputs then it shouldn't do

> By naive approach atm would be to just add .codec_names,
> .codec_dai_names and .codec_of_node to snd_soc_dai_link, and make their
> use mutually exclusive to the existing ones. That way, we don't need to
> touch any existing user.

May as well bite the bullet and do the refactoring, it should be
automatable.  There's also the fun of handling what happens when you
want to stream from one CODEC to another but I think that's second
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