dt-bindings: display: sii902x: Add HDMI audio bindings

The sii902x chip family supports also HDMI audio. Add binding for
describing the necessary i2s and mclk wiring for it.

Signed-off-by: Jyri Sarha <jsarha@ti.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/f790277fabc45f987f90075dd842368705226a84.1558964241.git.jsarha@ti.com

Documentation/devicetree/bindings/display/bridge/sii902x.txt

@@ -9,6 +9,40 @@ Optional properties:
 	  about hotplug events.
 	- reset-gpios: OF device-tree gpio specification for RST_N pin.
 
+	HDMI audio properties:
+	- #sound-dai-cells: <0> or <1>. <0> if only i2s or spdif pin
+	   is wired, <1> if the both are wired. HDMI audio is
+	   configured only if this property is found.
+	- sil,i2s-data-lanes: Array of up to 4 integers with values of 0-3
+	   Each integer indicates which i2s pin is connected to which
+	   audio fifo. The first integer selects i2s audio pin for the
+	   first audio fifo#0 (HDMI channels 1&2), second for fifo#1
+	   (HDMI channels 3&4), and so on. There is 4 fifos and 4 i2s
+	   pins (SD0 - SD3). Any i2s pin can be connected to any fifo,
+	   but there can be no gaps. E.g. an i2s pin must be mapped to
+	   fifo#0 and fifo#1 before mapping a channel to fifo#2. Default
+	   value is <0>, describing SD0 pin beiging routed to hdmi audio
+	   fifo #0.
+	- clocks: phandle and clock specifier for each clock listed in
+           the clock-names property
+	- clock-names: "mclk"
+	   Describes SII902x MCLK input. MCLK is used to produce
+	   HDMI audio CTS values. This property is required if
+	   "#sound-dai-cells"-property is present. This property follows
+	   Documentation/devicetree/bindings/clock/clock-bindings.txt
+	   consumer binding.
+
+	If HDMI audio is configured the sii902x device becomes an I2S
+	and/or spdif audio codec component (e.g a digital audio sink),
+	that can be used in configuring a full audio devices with
+	simple-card or audio-graph-card binding. See their binding
+	documents on how to describe the way the sii902x device is
+	connected to the rest of the audio system:
+	Documentation/devicetree/bindings/sound/simple-card.txt
+	Documentation/devicetree/bindings/sound/audio-graph-card.txt
+	Note: In case of the audio-graph-card binding the used port
+	index should be 3.
+
 Optional subnodes:
 	- video input: this subnode can contain a video input port node
 	  to connect the bridge to a display controller output (See this
@@ -21,6 +55,12 @@ Example:
 		compatible = "sil,sii9022";
 		reg = <0x39>;
 		reset-gpios = <&pioA 1 0>;
+
+		#sound-dai-cells = <0>;
+		sil,i2s-data-lanes = < 0 1 2 >;
+		clocks = <&mclk>;
+		clock-names = "mclk";
+
 		ports {
 			#address-cells = <1>;
 			#size-cells = <0>;