dt-bindings: usb: uac2: Add Feature Unit bindings

Add initial Feature Unit bindings allowing user to place the Feature
Unit inside UAC2 instance description. Currently the bindings facilitate
only specifying which controls are available on the Primary channel 0
and on each Logical channel. The number of Logical channels has to be
derived from data-source property.

Signed-off-by: Tomasz Moń <[email protected]>

Author: tmon-nordic

dts/bindings/usb/uac2/zephyr,uac2-feature-unit.yaml

@@ -0,0 +1,134 @@
+# Copyright (c) 2024 Nordic Semiconductor ASA
+# SPDX-License-Identifier: Apache-2.0
+
+description: USB Audio Class 2 Feature Unit entity
+
+compatible: "zephyr,uac2-feature-unit"
+
+# string-array properties start with Primary channel 0 and follow with Logical
+# channel(s). The "not-present" value is allowed to facilitate having controls
+# that are not present on the Primary channel, but only present at the Logical
+# channel(s).
+
+properties:
+  data-source:
+    type: phandle
+    description: Unit or Terminal to which this Feature Unit is connected
+
+  mute-control:
+    type: string-array
+    description: Mute Control capabilities
+    enum:
+      - "read-only"
+      - "host-programmable"
+      - "not-present"
+
+  volume-control:
+    type: string-array
+    description: Volume Control capabilities
+    enum:
+      - "read-only"
+      - "host-programmable"
+      - "not-present"
+
+  bass-control:
+    type: string-array
+    description: Bass Control capabilities
+    enum:
+      - "read-only"
+      - "host-programmable"
+      - "not-present"
+
+  mid-control:
+    type: string-array
+    description: Mid Control capabilities
+    enum:
+      - "read-only"
+      - "host-programmable"
+      - "not-present"
+
+  treble-control:
+    type: string-array
+    description: Treble Control capabilities
+    enum:
+      - "read-only"
+      - "host-programmable"
+      - "not-present"
+
+  graphic-equalizer-control:
+    type: string-array
+    description: Graphic Equalizer capabilities
+    enum:
+      - "read-only"
+      - "host-programmable"
+      - "not-present"
+
+  automatic-gain-control:
+    type: string-array
+    description: Automatic Gain Control capabilities
+    enum:
+      - "read-only"
+      - "host-programmable"
+      - "not-present"
+
+  delay-control:
+    type: string-array
+    description: Delay Control capabilities
+    enum:
+      - "read-only"
+      - "host-programmable"
+      - "not-present"
+
+  bass-boost-control:
+    type: string-array
+    description: Bass Boost Control capabilities
+    enum:
+      - "read-only"
+      - "host-programmable"
+      - "not-present"
+
+  loundness-control:
+    type: string-array
+    description: Loundness Control capabilities
+    enum:
+      - "read-only"
+      - "host-programmable"
+      - "not-present"
+
+  input-gain-control:
+    type: string-array
+    description: Input Gain Control capabilities
+    enum:
+      - "read-only"
+      - "host-programmable"
+      - "not-present"
+
+  input-gain-pad-control:
+    type: string-array
+    description: Input Gain Pad Control capabilities
+    enum:
+      - "read-only"
+      - "host-programmable"
+      - "not-present"
+
+  phase-inverter-control:
+    type: string-array
+    description: Phase Inverter Control capabilities
+    enum:
+      - "read-only"
+      - "host-programmable"
+      - "not-present"
+
+  underflow-control:
+    type: string-array
+    description: Underflow Control capabilities
+    enum:
+      - "read-only"
+      - "not-present"
+
+  overflow-control:
+    type: string-array
+    description: Overflow Control capabilities
+    enum:
+      - "read-only"
+      - "not-present"