dt-bindings: clock: Add Apple NCO

The NCO block found on Apple SoCs is a programmable clock generator
performing fractional division of a high frequency input clock.
Reviewed-by: Mark Kettenis <kettenis@openbsd.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Martin Povišer <povik+lin@cutebit.org>
Link: https://lore.kernel.org/r/20220208183411.61090-2-povik+lin@cutebit.orgSigned-off-by: Stephen Boyd <sboyd@kernel.org>

Documentation/devicetree/bindings/clock/apple,nco.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/clock/apple,nco.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Apple SoCs' NCO block
+
+maintainers:
+  - Martin Povišer <povik+lin@cutebit.org>
+
+description: |
+  The NCO (Numerically Controlled Oscillator) block found on Apple SoCs
+  such as the t8103 (M1) is a programmable clock generator performing
+  fractional division of a high frequency input clock.
+
+  It carries a number of independent channels and is typically used for
+  generation of audio bitclocks.
+
+properties:
+  compatible:
+    items:
+      - enum:
+          - apple,t6000-nco
+          - apple,t8103-nco
+      - const: apple,nco
+
+  clocks:
+    description:
+      Specifies the reference clock from which the output clocks
+      are derived through fractional division.
+    maxItems: 1
+
+  '#clock-cells':
+    const: 1
+
+  reg:
+    maxItems: 1
+
+required:
+  - compatible
+  - clocks
+  - '#clock-cells'
+  - reg
+
+additionalProperties: false
+
+examples:
+  - |
+    nco_clkref: clock-ref {
+      compatible = "fixed-clock";
+      #clock-cells = <0>;
+      clock-frequency = <900000000>;
+      clock-output-names = "nco-ref";
+    };
+
+    nco: clock-controller@23b044000 {
+      compatible = "apple,t8103-nco", "apple,nco";
+      reg = <0x3b044000 0x14000>;
+      #clock-cells = <1>;
+      clocks = <&nco_clkref>;
+    };