ASoC: meson: add axg sound card DT bindings documentation

Add the DT bindings documentation for axg sound card
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/amlogic,axg-sound-card.txt

+Amlogic AXG sound card:
+
+Required properties:
+
+- compatible: "amlogic,axg-sound-card"
+- amlogic,name : User specified audio sound card name, one string
+
+Optional properties:
+
+- amlogic,aux-devs : List of phandles pointing to auxiliary devices
+- amlogic,widgets : Please refer to widgets.txt.
+- amlogic,routing : A list of the connections between audio components.
+
+Subnodes:
+
+- amlogic,dai-link: Container for dai-link level properties and the
+		    CODEC sub-nodes. There should be at least one (and
+		    probably) subnode of this type.
+
+Required dai-link properties:
+
+- sound-dai: phandle and port of the CPU DAI.
+
+Required TDM Backend dai-link properties:
+- dai-format : CPU/CODEC common audio format
+
+Optional TDM Backend dai-link properties:
+- dai-tdm-slot-rx-mask-{0,1,2,3}: Receive direction slot masks
+- dai-tdm-slot-tx-mask-{0,1,2,3}: Transmit direction slot masks
+				  When omitted, mask is assumed to have to no
+				  slots. A valid must have at one slot, so at
+				  least one these mask should be provided with
+				  an enabled slot.
+- dai-tdm-slot-num : Please refer to tdm-slot.txt.
+		     If omitted, slot number is set to accommodate the largest
+		     mask provided.
+- dai-tdm-slot-width : Please refer to tdm-slot.txt. default to 32 if omitted.
+- mclk-fs : Multiplication factor between stream rate and mclk
+
+Backend dai-link subnodes:
+
+- codec: dai-link representing backend links should have at least one subnode.
+	 One subnode for each codec of the dai-link.
+	 dai-link representing frontend links have no codec, therefore have no
+	 subnodes
+
+Required codec subnodes properties:
+
+- sound-dai: phandle and port of the CODEC DAI.
+
+Optional codec subnodes properties:
+
+- dai-tdm-slot-tx-mask : Please refer to tdm-slot.txt.
+- dai-tdm-slot-rx-mask : Please refer to tdm-slot.txt.
+
+Example:
+
+sound {
+	compatible = "amlogic,axg-sound-card";
+	amlogic,name = "AXG-S420";
+	amlogic,aux-devs = <&tdmin_a>, <&tdmout_c>;
+	amlogic,widgets = "Line", "Lineout",
+			  "Line", "Linein",
+			  "Speaker", "Speaker1 Left",
+			  "Speaker", "Speaker1 Right";
+			  "Speaker", "Speaker2 Left",
+			  "Speaker", "Speaker2 Right";
+	amlogic,routing = "TDMOUT_C IN 0", "FRDDR_A OUT 2",
+			  "SPDIFOUT IN 0", "FRDDR_A OUT 3",
+			  "TDM_C Playback", "TDMOUT_C OUT",
+			  "TDMIN_A IN 2", "TDM_C Capture",
+			  "TDMIN_A IN 5", "TDM_C Loopback",
+			  "TODDR_A IN 0", "TDMIN_A OUT",
+			  "Lineout", "Lineout AOUTL",
+			  "Lineout", "Lineout AOUTR",
+			  "Speaker1 Left", "SPK1 OUT_A",
+			  "Speaker2 Left", "SPK2 OUT_A",
+			  "Speaker1 Right", "SPK1 OUT_B",
+			  "Speaker2 Right", "SPK2 OUT_B",
+			  "Linein AINL", "Linein",
+			  "Linein AINR", "Linein";
+
+	amlogic,dai-link@0 {
+		sound-dai = <&frddr_a>;
+	};
+
+	amlogic,dai-link@1 {
+		sound-dai = <&toddr_a>;
+	};
+
+	amlogic,dai-link@2 {
+		sound-dai = <&tdmif_c>;
+		dai-format = "i2s";
+		dai-tdm-slot-tx-mask-2 = <1 1>;
+		dai-tdm-slot-tx-mask-3 = <1 1>;
+		dai-tdm-slot-rx-mask-1 = <1 1>;
+		mclk-fs = <256>;
+
+		codec@0 {
+			sound-dai = <&lineout>;
+		};
+
+		codec@1 {
+			sound-dai = <&speaker_amp1>;
+		};
+
+		codec@2 {
+			sound-dai = <&speaker_amp2>;
+		};
+
+		codec@3 {
+			sound-dai = <&linein>;
+		};
+
+	};
+
+	amlogic,dai-link@4 {
+		sound-dai = <&spdifout>;
+
+		codec {
+			sound-dai = <&spdif_dit>;
+		};
+	};
+};