[alsa-devel] simle-card DT style for DPCM

[Kuninori Morimoto]

Hi Mark

> I think here what I'd expect to see is only one CPU DAI specified for
> the back end link in the CPU that is actually linked to the CODEC and
> the front ends being worked out by the drivers, unless there are systems
> where the set of front ends can be configured at system build time (as
> opposed to from software at runtime) somehow.

This means BE don't know who is FE.
The implementation can be more easy if it has
connect-to / connect-from property
(I'm not sure this is good naming...)

So, how about this ?
In pattern 3 case, it can be FE/BE if connect-to / connect-from was added,
otherwise, it will be normal DAI link.
connect-to / connect-from can be used if FE/BE were implemented
in different driver (pattern 3 indicates simle-card is BE)
We use pattern2 if FE/BE was not separated.

---------------------------------------
pattern 1: use DPCM in simple-card
---------------------------------------

It is supported, but it should use pattern 2 case.
This is sample of connect-to / connect-from.
see pattern 3

sound {
	compatible = "simple-audio-card";
	...

	/* Front End */
	dai_link0: simple-audio-card,dai-link at 0 {
		...
		connect-to = <&dai-link1>;

		cpu { ... };
		codec { ... };
	}

	/* Back End */
	dai_link1: simple-audio-card,dai-link at 1 {
		...
		connect-from = <&dai-link0>;

		cpu { ... };
		codec { ... };
	}
}

---------------------------------------
pattern 2: use DPCM in 1 simple-card
---------------------------------------
sound {
	compatible = "simple-audio-card";
	...

	simple-audio-card,dai-link {
		...
		cpu at 0 { ... };   /* FE-cpu *//* FE-codec is dummy */
		cpu at 1 { ... };   /* BE-cpu */
		codec at 1 { ... }; /* BE-codec */
	}
}

---------------------------------------
pattern 3: use DPCM in simple-card and other driver
---------------------------------------
sound {
	compatible = "simple-audio-card";
	...

	dai_link: simple-audio-card,dai-link {
		...
		cpu { ... };
		codec { ... };
	}
}

--
foo-bar-link: foo-bar-sound {
	compatible = "foo-bar-sound";

        ...
	remote = <&dai-link>; /* foo-bar style FE
	                       * same as "connect-to" in simple-card
	                       */
};

&dai_link {
	/* Back End */
	connect-from = <&foo-bar-link>;
};



Best regards
---
Kuninori Morimoto