dt-bindings: cpufreq: Document Qualcomm Shikra SoC EPSS

The Qualcomm Shikra cpufreq hardware is functionally identical to EPSS,
but supports only up to 12 frequency lookup table (LUT) entries. Introduce
Shikra specific bindings to represent this constrained EPSS variant.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
Signed-off-by: Imran Shaik <imran.shaik@oss.qualcomm.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

Documentation/devicetree/bindings/cpufreq/qcom,shikra-epss.yaml

@@ -0,0 +1,96 @@
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/cpufreq/qcom,shikra-epss.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Qualcomm Shikra SoC EPSS
+
+maintainers:
+  - Imran Shaik <imran.shaik@oss.qualcomm.com>
+  - Taniya Das <taniya.das@oss.qualcomm.com>
+
+description: |
+  EPSS is a hardware engine used by some Qualcomm SoCs to manage
+  frequency in hardware. It is capable of controlling frequency for
+  multiple clusters.
+
+  The Qualcomm Shikra SoC EPSS supports up to 12 frequency lookup table
+  (LUT) entries.
+
+properties:
+  compatible:
+    enum:
+      - qcom,shikra-epss
+
+  reg:
+    items:
+      - description: Frequency domain 0 register region
+      - description: Frequency domain 1 register region
+
+  reg-names:
+    items:
+      - const: freq-domain0
+      - const: freq-domain1
+
+  clocks:
+    items:
+      - description: XO Clock
+      - description: GPLL0 Clock
+
+  clock-names:
+    items:
+      - const: xo
+      - const: alternate
+
+  interrupts:
+    items:
+      - description: IRQ line for DCVSH 0
+      - description: IRQ line for DCVSH 1
+
+  interrupt-names:
+    items:
+      - const: dcvsh-irq-0
+      - const: dcvsh-irq-1
+
+  '#freq-domain-cells':
+    const: 1
+
+  '#clock-cells':
+    const: 1
+
+required:
+  - compatible
+  - reg
+  - clocks
+  - clock-names
+  - interrupts
+  - interrupt-names
+  - '#freq-domain-cells'
+  - '#clock-cells'
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/clock/qcom,rpmcc.h>
+    #include <dt-bindings/interrupt-controller/arm-gic.h>
+
+    soc {
+      #address-cells = <1>;
+      #size-cells = <1>;
+
+      cpufreq@fd91000 {
+        compatible = "qcom,shikra-epss";
+        reg = <0x0fd91000 0x1000>, <0x0fd92000 0x1000>;
+        reg-names = "freq-domain0", "freq-domain1";
+        clocks = <&rpmcc RPM_SMD_XO_CLK_SRC>, <&gpll0>;
+        clock-names = "xo", "alternate";
+        interrupts = <GIC_SPI 30 IRQ_TYPE_LEVEL_HIGH>,
+                     <GIC_SPI 31 IRQ_TYPE_LEVEL_HIGH>;
+        interrupt-names = "dcvsh-irq-0", "dcvsh-irq-1";
+        #freq-domain-cells = <1>;
+        #clock-cells = <1>;
+      };
+    };
+...