dt-bindings: soundwire: add slave bindings

This patch adds bindings for Soundwire Slave devices that includes how
SoundWire enumeration address and Link ID are used to represented in
SoundWire slave device tree nodes.
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20190829163514.11221-2-srinivas.kandagatla@linaro.orgSigned-off-by: Vinod Koul <vkoul@kernel.org>

Documentation/devicetree/bindings/soundwire/soundwire-controller.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/soundwire/soundwire-controller.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: SoundWire Controller Generic Binding
+
+maintainers:
+  - Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
+  - Vinod Koul <vkoul@kernel.org>
+
+description: |
+  SoundWire busses can be described with a node for the SoundWire controller
+  device and a set of child nodes for each SoundWire slave on the bus.
+
+properties:
+  $nodename:
+    pattern: "^soundwire(@.*)?$"
+
+  "#address-cells":
+    const: 2
+
+  "#size-cells":
+    const: 0
+
+patternProperties:
+  "^.*@[0-9a-f],[0-9a-f]$":
+    type: object
+
+    properties:
+      compatible:
+        pattern: "^sdw[0-9a-f]{1}[0-9a-f]{4}[0-9a-f]{4}[0-9a-f]{2}$"
+        description: Is the textual representation of SoundWire Enumeration
+          address. compatible string should contain SoundWire Version ID,
+          Manufacturer ID, Part ID and Class ID in order and shall be in
+          lower-case hexadecimal with leading zeroes.
+          Valid sizes of these fields are
+          Version ID is 1 nibble, number '0x1' represents SoundWire 1.0
+          and '0x2' represents SoundWire 1.1 and so on.
+          MFD is 4 nibbles
+          PID is 4 nibbles
+          CID is 2 nibbles
+          More Information on detail of encoding of these fields can be
+          found in MIPI Alliance DisCo & SoundWire 1.0 Specifications.
+
+      reg:
+        maxItems: 1
+        description:
+          Link ID followed by Instance ID of SoundWire Device Address.
+
+    required:
+      - compatible
+      - reg
+
+required:
+  - "#address-cells"
+  - "#size-cells"
+
+examples:
+  - |
+    soundwire@c2d0000 {
+        #address-cells = <2>;
+        #size-cells = <0>;
+        reg = <0x0c2d0000 0x2000>;
+
+        speaker@0,1 {
+            compatible = "sdw10217201000";
+            reg = <0 1>;
+            powerdown-gpios = <&wcdpinctrl 2 0>;
+            #thermal-sensor-cells = <0>;
+        };
+
+        speaker@0,2 {
+            compatible = "sdw10217201000";
+            reg = <0 2>;
+            powerdown-gpios = <&wcdpinctrl 2 0>;
+            #thermal-sensor-cells = <0>;
+        };
+    };
+
+...