linux-kernel - Re: [PATCH] ASoC: make snd_soc_dai

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Date:	Wed, 1 Jan 2014 12:59:47 +0000
From:	Mark Brown <broonie@...nel.org>
To:	Jean-Francois Moine <moinejf@...e.fr>
Cc:	Liam Girdwood <lgirdwood@...il.com>,
	Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.de>,
	alsa-devel@...a-project.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ASoC: make snd_soc_dai_link more symmetrical

On Tue, Dec 31, 2013 at 06:44:30PM +0100, Jean-Francois Moine wrote:
> Mark Brown <broonie@...nel.org> wrote:

> > It's possible there is a benefit I'm just not seeing but you'll need to
> > tell me.

> The first benefit I got was in the front-end definition: the codec side
> is the dummy codec, and this one has no phandle.

That's a sign that you're putting Linux implementation details into your
DT - remember, DT is supposed to be implementation neutral.

> Then, finding the CODEC DAI from phandle asks for more code
> (of_xlate_dai_name in the CODEC drivers) and finding it from the CODEC

They should be able to use a default there; I'd expect that just to be
making the IDs the same as the index into the array or the ID field.

> name asks for a double loop in soc_bind_dai_link. On the other way, a
> simple loop without any more change may be used when the DAI is simply
> specified by its name. I would say that the DAI name is more meaningful

Then as soon as anything else starts using the same name for some reason
the binding stops being useful.

> than a DAI index and that it is less subject to internal changes of the
> CODEC driver.

Obviously the numbers that get assigned become a part of the ABI and
can't be changed.  Now that we have preprocessor support for DT the
plain text can be done with that, though for a lot of devices that won't
be needed as the devices are just numbered anyway.

> Eventually, I don't think that, using only the name of the CODEC side
> DAI to identify it, is not more fragile than identifying the CPU side
> of the DAI link by its name.

This doesn't mean it's a good idea to do it - as you will remember I
said I expected things to want to go more towards using phandle plus ID 
for everything.  

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