[alsa-devel] Different codecs for playback and capture?

[Ricard Wanderlof]

On Thu, 4 Jun 2015, Lars-Peter Clausen wrote:

> > Ideally it would have been some sort of 'if (!codec_stream->defined)' but
> > there isn't such a member in struct snd_soc_dai . I've gone with 'if
> > (!codec_stream->rates && !codec_stream->formats)', thinking that if a
> > codec doesn't support any rates or formats, it probably doesn't support
> > that mode at all (else it's rather meaningless). In fact, one of these
> > (rates or formats) would probably suffice, with a comment explaining what
> > we're really trying to do.
> >
> > The next problem is that when trying to set hw params, something in the
> > framework or the individual codec driver hw_params() bails out saying it
> > can't set the intended parameters. Looking at that right now to see if it
> > can be solved in a similar way.
> 
> The best way to solve this is probably to introduce a helper function bool 
> snd_soc_dai_stream_valid(struct snd_soc_dai *dai, int stream) that 
> implements the logic for detecting whether a DAI supports a playback or 
> capture stream. And then whenever iterating over the codec_dais field for 
> stream operations skip those which don't support the stream.

Yes. The question is, exactly what should the helper function use to 
determine stream support. Is it sufficient to check for 
dai->driver->playback/capture->rates != 0 ?

I'm a bit worried at the 'whenever iterating over the codec_dais field'. 
There are 50+ places which iterate over codec_dais, mostly in soc-pcm.c 
and soc-core.c . Of course code could be added to all locations, but it 
starts to feel like the wrong approach, i.e. like the iteration itself 
should be done in a separate function (which doesn't really seem viable in 
itself; this isn't glib).

For the hardware I have here, there are two places where it is necessary; 
admittedly, this particular hardware is pretty simple (on the other hand, 
I would suppose that most situations with this type of split 
playback/capture would be for cases where there are simple codecs or I2S 
microphones that only support one of the modes).

What I'm getting at is that, disregarding the helper function which is 
needed anyway, perhaps I should just fix the two locations needed for now, 
and leave the rest to be fixed when the need arises? I'm not sure they all 
need to be modified in this way.

/Ricard
-- 
Ricard Wolf Wanderlöf                           ricardw(at)axis.com
Axis Communications AB, Lund, Sweden            www.axis.com
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