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

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Date:	Wed, 19 Mar 2014 20:31:45 +0100
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Mark Brown <broonie@...nel.org>
CC:	Jyri Sarha <jsarha@...com>, Jean-Francois Moine <moinejf@...e.fr>,
	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 03/19/2014 08:21 PM, Mark Brown wrote:
> On Wed, Mar 19, 2014 at 09:15:14PM +0200, Jyri Sarha wrote:
>> On 03/19/2014 08:51 PM, Lars-Peter Clausen wrote:
>
>>> When does this make sense? Either the bitclock is inverted for all of
>>> them or for none.
>
>> Definition of clock signal and it's inversion varies between chip
>> manufacturers and sometimes it may not be possible to get all the dai
>> drivers to work identically in this respect. Because of this in some cases
>> there may be a need to set the inversion bit only at one end of the link.
>
> No, Linux has a definition of all the clock modes which applies to all
> devices regardless of what the manufacturer documents in their
> datasheet.
>

Yep. The clock properties are well defined for the different modes that can 
be specified in the format property. It's up to the driver to translate this 
to driver specific settings. If two drivers behave differently for the same 
mode one of them (or both) are broken.

We should probably add the definitions for the different formats to the DT 
bindings. E.g. what is default, what is inverted polarity, etc.

- Lars
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