[alsa-devel] Question about FE & BE DPCM

[Daniel Baluta]

Hi Morimoto-san,

I'm really confused on what exactly is Front End and Back End.

Is FE a DAI or a DAI link or part of a DAI link?

In simple-card.c there is simple_dai_link_of_dpcm function:

struct snd_soc_dai_link_component *codecs = dai_link->codecs;

»       /* BE is dummy */
»       »       codecs->of_node»»       = NULL;
»       »       codecs->dai_name»       = "snd-soc-dummy-dai";
»       »       codecs->name»   »       = "snd-soc-dummy";

»       »       /* FE settings */
»       »       dai_link->dynamic»      »       = 1;
»       »       dai_link->dpcm_merged_format»   = 1;

So, from here it looks like BE/FE are components being part of the same link.

Another thing is:

asoc_simple_canonicalize_platform function where it does say:

»        * DPCM BE can be no platform.
»        * Alloced memory will be waste, but not leak.
»        */
»       if (!dai_link->platforms->of_node)
»       »       dai_link->num_platforms = 0;

But I do want to create a BE with a platform. So, should I try to
revert the following
patch:

commit 794fcee8da3c0c8a01b08ecad1c181cb0a622868
Author: Kuninori Morimoto <kuninori.morimoto.gx at renesas.com>
Date:   Wed Jul 10 17:01:12 2019 +0900

    ASoC: simple-card-utils: care no Platform for DPCM

    commit 34614739988ad ("ASoC: soc-core: support dai_link with
    platforms_num != 1") supports multi Platform, and
    commit 9f3eb91753451 ("ASoC: simple-card-utils: consider CPU-Platform
    possibility") removed no Platform from simple-card.

    Multi Platform is now checking both Platform name/of_node are NULL case.
    But in normal case, DPCM be doesn't have Platform.



Basically, what I want to do is: after the DAI link is created to call:
snd_soc_fixup_dai_links_platform_name function to set a proper name
for BE platform.

The problem is that above mentioned patch sets dai_link->num_platforms = 0;
so even the name is set the platform component is not probed.

thanks,
Daniel.