dt-bindings: clock: Document Exynos7885 CMU bindings

Provide dt-schema documentation for Exynos7885 SoC clock controller.
Description is modified from Exynos850 clock controller documentation as
I couldn't describe it any better, that was written by Sam Protsenko.
Signed-off-by: David Virag <virag.david003@gmail.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Reviewed-by: Sam Protsenko <semen.protsenko@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20211206153124.427102-3-virag.david003@gmail.com

Documentation/devicetree/bindings/clock/samsung,exynos7885-clock.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/clock/samsung,exynos7885-clock.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Samsung Exynos7885 SoC clock controller
+
+maintainers:
+  - Dávid Virág <virag.david003@gmail.com>
+  - Chanwoo Choi <cw00.choi@samsung.com>
+  - Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
+  - Sylwester Nawrocki <s.nawrocki@samsung.com>
+  - Tomasz Figa <tomasz.figa@gmail.com>
+
+description: |
+  Exynos7885 clock controller is comprised of several CMU units, generating
+  clocks for different domains. Those CMU units are modeled as separate device
+  tree nodes, and might depend on each other. The root clock in that root tree
+  is an external clock: OSCCLK (26 MHz). This external clock must be defined
+  as a fixed-rate clock in dts.
+
+  CMU_TOP is a top-level CMU, where all base clocks are prepared using PLLs and
+  dividers; all other leaf clocks (other CMUs) are usually derived from CMU_TOP.
+
+  Each clock is assigned an identifier and client nodes can use this identifier
+  to specify the clock which they consume. All clocks available for usage
+  in clock consumer nodes are defined as preprocessor macros in
+  'dt-bindings/clock/exynos7885.h' header.
+
+properties:
+  compatible:
+    enum:
+      - samsung,exynos7885-cmu-top
+      - samsung,exynos7885-cmu-core
+      - samsung,exynos7885-cmu-peri
+
+  clocks:
+    minItems: 1
+    maxItems: 10
+
+  clock-names:
+    minItems: 1
+    maxItems: 10
+
+  "#clock-cells":
+    const: 1
+
+  reg:
+    maxItems: 1
+
+allOf:
+  - if:
+      properties:
+        compatible:
+          contains:
+            const: samsung,exynos7885-cmu-top
+
+    then:
+      properties:
+        clocks:
+          items:
+            - description: External reference clock (26 MHz)
+
+        clock-names:
+          items:
+            - const: oscclk
+
+  - if:
+      properties:
+        compatible:
+          contains:
+            const: samsung,exynos7885-cmu-core
+
+    then:
+      properties:
+        clocks:
+          items:
+            - description: External reference clock (26 MHz)
+            - description: CMU_CORE bus clock (from CMU_TOP)
+            - description: CCI clock (from CMU_TOP)
+            - description: G3D clock (from CMU_TOP)
+
+        clock-names:
+          items:
+            - const: oscclk
+            - const: dout_core_bus
+            - const: dout_core_cci
+            - const: dout_core_g3d
+
+  - if:
+      properties:
+        compatible:
+          contains:
+            const: samsung,exynos7885-cmu-peri
+
+    then:
+      properties:
+        clocks:
+          items:
+            - description: External reference clock (26 MHz)
+            - description: CMU_PERI bus clock (from CMU_TOP)
+            - description: SPI0 clock (from CMU_TOP)
+            - description: SPI1 clock (from CMU_TOP)
+            - description: UART0 clock (from CMU_TOP)
+            - description: UART1 clock (from CMU_TOP)
+            - description: UART2 clock (from CMU_TOP)
+            - description: USI0 clock (from CMU_TOP)
+            - description: USI1 clock (from CMU_TOP)
+            - description: USI2 clock (from CMU_TOP)
+
+        clock-names:
+          items:
+            - const: oscclk
+            - const: dout_peri_bus
+            - const: dout_peri_spi0
+            - const: dout_peri_spi1
+            - const: dout_peri_uart0
+            - const: dout_peri_uart1
+            - const: dout_peri_uart2
+            - const: dout_peri_usi0
+            - const: dout_peri_usi1
+            - const: dout_peri_usi2
+
+required:
+  - compatible
+  - "#clock-cells"
+  - clocks
+  - clock-names
+  - reg
+
+additionalProperties: false
+
+examples:
+  # Clock controller node for CMU_PERI
+  - |
+    #include <dt-bindings/clock/exynos7885.h>
+
+    cmu_peri: clock-controller@10010000 {
+        compatible = "samsung,exynos7885-cmu-peri";
+        reg = <0x10010000 0x8000>;
+        #clock-cells = <1>;
+
+        clocks = <&oscclk>,
+                 <&cmu_top CLK_DOUT_PERI_BUS>,
+                 <&cmu_top CLK_DOUT_PERI_SPI0>,
+                 <&cmu_top CLK_DOUT_PERI_SPI1>,
+                 <&cmu_top CLK_DOUT_PERI_UART0>,
+                 <&cmu_top CLK_DOUT_PERI_UART1>,
+                 <&cmu_top CLK_DOUT_PERI_UART2>,
+                 <&cmu_top CLK_DOUT_PERI_USI0>,
+                 <&cmu_top CLK_DOUT_PERI_USI1>,
+                 <&cmu_top CLK_DOUT_PERI_USI2>;
+        clock-names = "oscclk",
+                      "dout_peri_bus",
+                      "dout_peri_spi0",
+                      "dout_peri_spi1",
+                      "dout_peri_uart0",
+                      "dout_peri_uart1",
+                      "dout_peri_uart2",
+                      "dout_peri_usi0",
+                      "dout_peri_usi1",
+                      "dout_peri_usi2";
+    };
+
+...