[alsa-devel] [PATCH v9 1/4] drm/i2c: tda998x: Add DT support for audio

[Jean-Francois Moine]

On Tue, 13 Jan 2015 19:54:15 +0000
Russell King - ARM Linux <linux at arm.linux.org.uk> wrote:

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

#address-cells and #size-cells may be defined in any of the upper
parent, so, as it is defined in the device, it is not needed in the
port (see of_n_addr_cells in drivers/of/base.c).

Well, I am a bit lost between (only one source / many channels - I2S
busses) and (many sources / one I2s bus!).

Anyway, I don't understand your example.
I'd expect that a port would be a DAI.

If yes, when playing is active, both endpoints receive an audio stream
from the remote audio devices, and the AP register is always set to
0x07 (= 0x01 | 0x02 | 0x04).
Then, it would have been simpler to have:

 	#address-cells = <1>;
 	#size-cells = <0>;
 	...
         port at 7 {                        /* AP1,2 = I2S */
                 port-type = "i2s";
                 reg = <0x07>;		/* WS + AP1 + AP2 */
                 tda998x_i2s1: endpoint at 1 {
                         remote-endpoint = <&audio1_i2s>;
                 };
                 tda998x_i2s2: endpoint at 2 {
                         remote-endpoint = <&audio2_i2s>;
                 };
         };

If no, the two DAIs must be created from the endpoints, permitting
streaming on i2s1 alone, i2s2 alone or both i2s1+i2s2 at the same time.
Then, it would have been simpler to define the DAIs from the ports:

	#address-cells = <1>;
 	#size-cells = <0>;
 	...
         port at 3 {                        /* AP1 = I2S */
                 port-type = "i2s";
                 reg = <0x03>;		/* WS + AP1 */
                 tda998x_i2s1: endpoint {
                         remote-endpoint = <&audio1_i2s>;
                 };
         };
         port at 5 {                        /* AP2 = I2S */
                 port-type = "i2s";
                 reg = <0x05>;		/* WS + AP2 */
                 tda998x_i2s1: endpoint {
                         remote-endpoint = <&audio1_i2s>;
                 };
	};

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