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

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Date:	Tue, 13 Jan 2015 19:54:15 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Jyri Sarha <jsarha@...com>
Cc:	Jean-Francois Moine <moinejf@...e.fr>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	Andrew Jackson <Andrew.Jackson@....com>,
	Mark Brown <broonie@...nel.org>,
	Dave Airlie <airlied@...il.com>,
	"alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v9 1/4] drm/i2c: tda998x: Add DT support for audio

On Tue, Jan 13, 2015 at 09:41:01PM +0200, Jyri Sarha wrote:
> On 01/13/2015 09:26 PM, Russell King - ARM Linux wrote:
> >SCLK: _~_~_~_~_~_~_~_~_~_~_~_~_~_~_~_~_~_~_~_~_~_~_~_~_~_~_~_~_~_~_~_~_~_
> >   WS: __~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~________________________________~
> >I2S1: llmm............................llmm............................llm
> >I2S2: llmm............................llmm............................llm
> >I2S3: llmm............................llmm............................llm
> >I2S4: llmm............................llmm............................llm
> >
> >So, what I'm saying is that it is_impossible_  to drive the TDA998x using
> >multiple I2S streams which are not produced by the same I2S block.
> 
> This is besides the point, but it is possible that one of the multiple I2S
> blocks is the bit-clock and frame-clock master to the i2s bus and the others
> are slaves to it (banging their bits according to SCLK and WS of the I2S
> master). However, in this situation there really is only one i2s bus with
> multiple data pins.
> 
> Just my 0.02€ to this discussion.

Right, that's about the only way it could work.

To represent that in DT, I would imagine we'd need something like this:

	#address-cells = <1>;
	#size-cells = <0>;
	...
        port@1 {                        /* AP1,2 = I2S */
		#address-cells = <1>;
		#size-cells = <0>;
                port-type = "i2s";
                reg = <0x01>;		/* WS */
                tda998x_i2s1: endpoint@2 {
			reg = <0x02>;	/* AP1 */
                        remote-endpoint = <&audio1_i2s>;
                };
                tda998x_i2s2: endpoint@4 {
			reg = <0x04>;	/* AP2 */
                        remote-endpoint = <&audio2_i2s>;
                };
        };

where audio1_i2s is operating in master mode, and audio2_i2s is
operating in slave mode for both WS and SCLK.

If we can agree on that, then I'm happy with the proposed binding.
(Remember that #address-cells and #size-cells are required in the
parent where we have reg= in the child.)

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