linux-kernel - Re: [alsa-devel] [PATCH v3 4/4] ASoC: simple-card: Add DT documentation for multi-DAI links

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Date:	Mon, 17 Mar 2014 12:19:46 +0200
From:	Jyri Sarha <jsarha@...com>
To:	Jean-Francois Moine <moinejf@...e.fr>
Cc:	Mark Brown <broonie@...nel.org>, devicetree@...r.kernel.org,
	alsa-devel@...a-project.org, Xiubo Li <Li.Xiubo@...escale.com>,
	linux-kernel@...r.kernel.org,
	Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>
Subject: Re: [alsa-devel] [PATCH v3 4/4] ASoC: simple-card: Add DT
 documentation for multi-DAI links

On 2014-03-15 13:30, Jean-Francois Moine wrote:
> There may be many couples of CPU/CODEC DAI links.
> The example 2 is extracted from the Cubox DT.
> 
> Signed-off-by: Jean-Francois Moine <moinejf@...e.fr>
> ---
[...]

This binding forces all the dai links to share the same card level 
properties. I find it problematic in these cases:

>> - simple-audio-card,format		: CPU/CODEC common audio format.
>> 					  "i2s", "right_j", "left_j" , "dsp_a"
>> 					  "dsp_b", "ac97", "pdm", "msb", "lsb"

The code allows having the format parameter in sub nodes too, but the 
document does no mention it. Adding a mention would solve this problem 
at least partly.

Neither does the document mention that 
"simple-audio-card,bitclock-inversion" and 
"simple-audio-card,frame-inversion" are also allowed in card level. 
Currently the code uses simple bit-wise-or from card-level and dai-level 
daifmt parameters, which may lead to broken daifmt setting. However, 
this on directly related to this patch.

>> - dai-tdm-slot-num			: Please refer to tdm-slot.txt.
>> - dai-tdm-slot-width			: Please refer to tdm-slot.txt.

These properties are actually only taken from sub-nodes so the document 
is broken but the code is ok.

In general this binding would look better if another sub-node level 
would added for dai-link related properties, including the cpu and codec 
sub-nodes, but that would break the backwards compatibility.

Best regards,
Jyri
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