ASoC: meson: g12a: add toacodec dt-binding documentation

Add the DT bindings and documentation of the internal audio DAC glue found
on Amlogic g12a and sm1 SoC families
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Link: https://lore.kernel.org/r/20200221153607.1585499-2-jbrunet@baylibre.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/amlogic,g12a-toacodec.yaml

+# SPDX-License-Identifier: GPL-2.0
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/sound/amlogic,g12a-toacodec.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Amlogic G12a Internal DAC Control Glue
+
+maintainers:
+  - Jerome Brunet <jbrunet@baylibre.com>
+
+properties:
+  $nodename:
+    pattern: "^audio-controller@.*"
+
+  "#sound-dai-cells":
+    const: 1
+
+  compatible:
+    oneOf:
+      - items:
+        - const:
+            amlogic,g12a-toacodec
+      - items:
+        - enum:
+          - amlogic,sm1-toacodec
+        - const:
+            amlogic,g12a-toacodec
+
+  reg:
+    maxItems: 1
+
+  resets:
+    maxItems: 1
+
+required:
+  - "#sound-dai-cells"
+  - compatible
+  - reg
+  - resets
+
+examples:
+  - |
+    #include <dt-bindings/reset/amlogic,meson-g12a-audio-reset.h>
+
+    toacodec: audio-controller@740 {
+        compatible = "amlogic,g12a-toacodec";
+        reg = <0x0 0x740 0x0 0x4>;
+        #sound-dai-cells = <1>;
+        resets = <&clkc_audio AUD_RESET_TOACODEC>;
+    };

include/dt-bindings/sound/meson-g12a-toacodec.h

+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __DT_MESON_G12A_TOACODEC_H
+#define __DT_MESON_G12A_TOACODEC_H
+
+#define TOACODEC_IN_A	0
+#define TOACODEC_IN_B	1
+#define TOACODEC_IN_C	2
+#define TOACODEC_OUT	3
+
+#endif /* __DT_MESON_G12A_TOACODEC_H */