linux-kernel - Re: [PATCH v9 1/4] drm/i2c: tda998x: Add DT support for audio

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Message-ID: <20150109123036.4bc4bbf6@armhf>
Date:	Fri, 9 Jan 2015 12:30:36 +0100
From:	Jean-Francois Moine <moinejf@...e.fr>
To:	Jyri Sarha <jsarha@...com>
Cc:	Mark Brown <broonie@...nel.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Dave Airlie <airlied@...il.com>,
	Andrew Jackson <Andrew.Jackson@....com>,
	<alsa-devel@...a-project.org>, <devicetree@...r.kernel.org>,
	<dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v9 1/4] drm/i2c: tda998x: Add DT support for audio

On Fri, 9 Jan 2015 12:13:04 +0200
Jyri Sarha <jsarha@...com> wrote:

> On 01/08/2015 06:42 PM, Jean-Francois Moine wrote:
> >  From Andrew's datasheet, the TDA998x's which are handled by the tda998x
> > driver have only 4 input audio pins, the first two ones being either
> > S/PDIF or I2s, the last ones being I2S only.
> 
> AFAIK, SPDIF is always a single pin connection so only one pin needs to 
> be selected. But i2s need for pins for full 8 channel output.

There are 2 possible S/PDIF pins in the tda998x, and there may be many
audio chips with S/PDIF outputs.

> > So, the DT description could be reduced to a simple list indexed by
> > the pin number (= DAI number) and defining the protocol type.
> >
> > Examples:
> >
> > - for the Cubox:
> >
> > 	audio-inputs = "i2s", "spdif";
> >
> > - for some other board with I2S on the pins 3 and 4 only:
> >
> > 	audio-inputs = "none", "none", "i2s", "i2s";
> >
> > - for a fully wired TDA9983B (no driver yet):
> >
> > 	audio-inputs = "i2s", "i2s", "i2s", "i2s", "spdif";
> >
> 
> If you want to go closer to the original paradigm, then how about 
> defining following audio-port-names: i2s0, i2s1, i2s2, i2s3, and spdif. 
> With this approach we could go with your original binding with only 
> minor changes. A binding in your stereo i2s or spdif case would look 
> like this:
> 
> 	audio-ports = <0x04>, <0x03>;
> 	audio-port-names = "spdif", "i2s0";
> 
> A full 8 channel i2s or spdif output would look like this:
> 
> 	audio-ports = <0x04>, <0x03>, <0x02>, <0x01>, <0x00>;
> 	audio-port-names = "spdif", "i2s0", "i2s1", "i2s2", "i2s3";
> 
> This would also indicate the channel mapping to the audio pins (i2s0 for 
> first two channels, i2s1 for 3-4, etc.)
> 
> The code could for now just look for "i2s0" and the port names for 
> channels 3-8 could be ignored until they are needed.

In my original version, the audio-ports are a bitmap of the pins, the
bit 0 being the WS used for I2S. A fully wired tda998x would have been
as:

	audio-ports = <0x03>, <0x04>, <0x09>, <0x11>;
	audio-port-names = "i2s", "spdif", "i2s", "i2s";

With the new version, it would simply become:

	audio-inputs = "i2s", "spdif", "i2s", "i2s";

-- 
Ken ar c'hentañ	|	      ** Breizh ha Linux atav! **
Jef		|		http://moinejf.free.fr/
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