linux-kernel - Re: [PATCH 2/3] ASoC: twl4030: allow voice port to be connected externally.

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Message-ID: <20141110102551.2678d342@notabene.brown>
Date:	Mon, 10 Nov 2014 10:25:51 +1100
From:	NeilBrown <neilb@...e.de>
To:	Mark Brown <broonie@...nel.org>
Cc:	Mark Rutland <mark.rutland@....com>,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Liam Girdwood <lgirdwood@...il.com>,
	Rob Herring <robh+dt@...nel.org>,
	Peter Ujfalusi <peter.ujfalusi@...com>,
	GTA04 owners <gta04-owner@...delico.com>,
	devicetree@...r.kernel.org, alsa-devel@...a-project.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] ASoC: twl4030: allow voice port to be connected
 externally.

On Sat, 8 Nov 2014 09:26:22 +0000 Mark Brown <broonie@...nel.org> wrote:

> On Sat, Nov 08, 2014 at 11:38:03AM +1100, NeilBrown wrote:
> 
> > If voice port on twl4030 is not connected to a McBSP (or similar)
> > then we cannot configure the format the way we normally do for a DAI.
> 
> Yes we can, you need to represent the DAI link to whatever else the
> device is connected to in the driver like we do anything else - and in
> any case this isn't a device specific issue so we shouldn't be doing
> something driver specific to solve it.  Look at something like speyside.

Hi Mark,
 thanks for the reply ... I might need a little bit more help though.

I had a look at sound/soc/samsung/speyside.c, but I'm not entirely sure what
I'm looking for.
Presumably this is an audio processor not unlike the audio module in the
twl4030.

I see that there are 3 dai-links:
  CPU-DSP
  DSP-CODEC
  Baseband

Presumably "Baseband" is similar, in purpose at least, to the "voice"
interface on the twl4030.

Each dai-link has a "cpu_dai_name" and a "codec_dai_name", even though it
appears that only "CPU-DSP" is connected to the CPU.  Maybe that naming is
the source of some of my confusion.

"Baseband" declares
                .cpu_dai_name = "wm8996-aif2",
so wm8996 is something with 2 audio interfaces, (aif), and this is the second
one?  Maybe the  wm8996 is the audio module, so what is the "speyside"?

http://opensource.wolfsonmicro.com/content/speyside-audio

says it is a "reference platform".  Does that mean it is a board with a bunch
of chips soldered onto it?  If it were a board it should be described by a
dts file, not by a pile of C code (I thought), so I must be wrong about that.

In my case, I have a board with a GSM module and the twl4030 module.  Each
has an audio interface and these are connected.  I assume that I need to
express this connection in the dts file.
The GSM module doesn't currently appear in the dts file as it is usb-attached.
However I've been thinking that we will need to add it so we can express
power-on controls (twiddling some GPIOs).  So let's suppose we have the GSM
module in the dts file (child of a USB interface) and the twl4030 as well
(beneath an i2c interface).

The twl4030 needs to know the master/polarity of the clk/frm lines.  The GSM
module declares that these are.  So presumably we need some sort of linkage.
Ahhhh... I found Documentation/devicetree/bindings/sound/simple-card.txt

So I need to make the "voice" port on the twl4030 look like a "cpu" end of a
dai-link, and create a "codec" end in the GSM module, and use "sound-dai" to
point from the twl4030 to the GSM module.
Then I use frame-master, bitclock-master, bitclock-inversion, frame-inversion
for the settings I need.

I suspect I can make that work.

Am I on the right track?

Thanks,
NeilBrown

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