[alsa-devel] [RFT v3 3/3] ASoC: core: Add support for DAI multicodec

Lars-Peter Clausen lars at metafoo.de
Fri May 16 12:44:44 CEST 2014

On 05/15/2014 05:01 PM, Benoit Cousson wrote:
> Hi Lars,
> I'm struggling a little bit to understand one of your comment :-)
> On 26/04/2014 14:51, Lars-Peter Clausen wrote:
>> On 04/24/2014 02:01 PM, Benoit Cousson wrote:
>>> @@ -870,6 +876,10 @@ struct snd_soc_dai_link {
>>>        const struct device_node *codec_of_node;
>>>        /* You MUST specify the DAI name within the codec */
>>>        const char *codec_dai_name;
>>> +
>>> +    struct snd_soc_dai_link_component *codecs;
>> Should probably be const
> In fact, I don't think this is not possible, since this struct will be initialized at runtime in the legacy case when the regular codec struct is the one used by the driver.

That shouldn't be a problem. The const applies to the data the pointer 
points to, not the pointer itself.

> [...]
>>> @@ -1586,16 +1626,21 @@ static int soc_probe_link_dais(struct
>>> snd_soc_card *card, int num, int order)
>>>                            codec2codec_close_delayed_work);
>>>                /* link the DAI widgets */
>>> -            ret = soc_link_dai_widgets(card, dai_link,
>>> -                    cpu_dai, codec_dai);
>>> -            if (ret)
>>> -                return ret;
>>> +            for (i = 0; i < rtd->num_codecs; i++) {
>>> +                ret = soc_link_dai_widgets(card, dai_link,
>>> +                        cpu_dai, rtd->codec_dais[i]);
>> This will create a DAI link widget for each CODEC DAI. The DAI link
>> widget will configure the CPU and the CODEC DAI that are connected to
>> it. If there is one DAI link widget per CODEC DAI this means that the
>> CPU DAI will be connected to multiple DAI link widgets, which means it
>> will be configured once for each CODEC DAI (with possible conflicting
>> configurations).
> I've got that point, but now I'm wondering what struct should be per codec_dai. Should we consider one source and several sinks to represent the multiple codecs?

The soc_link_dai_widgets function should take the rtd as a parameter instead 
of the CODEC and CPU DAIs. Same goes for snd_soc_dapm_new_pcm() then you 
create one dai_link widget per stream (i.e. one for capture of there is 
capture support, one for playback if there is playback support). And then 
create the paths between the dai_link widgets and the DAI widgets accordingly.

>> So there should only be one DAI link widget per DAI link, with the CPU
>> DAI on one side and the CODEC DAIs on the other side. Note that you'll
>> also need to re-work snd_soc_dai_link_event() to handle multiple
>> inputs/outputs. I'd factor that part out into a separate patch.
> Here, I'm lost :-)
> What struct should be made multiple in that case?
> Should we consider that the following list can handle multiple sink/source?
> 	/* We only support a single source and sink, pick the first */
> 	source_p = list_first_entry(&w->sources, struct snd_soc_dapm_path,
> 				    list_sink);
> 	sink_p = list_first_entry(&w->sinks, struct snd_soc_dapm_path,
> 				  list_source);
> [...]

See the attached patch.

If you don't want to worry about these things for now it should be fine to 
add a check in soc_probe_link_dais() and make sure that num_codecs == 1 for 
the CODEC to CODEC case. This means we'll not support multi-codec links for 
CODEC to CODEC links, which should in my opinion be fine for now.

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