dt-bindings: cpufreq: Add mediatek,mt8196-cpufreq-hw binding

The MediaTek MT8196 SoC has new cpufreq hardware, with added memory
register ranges to control Dynamic-Voltage-Frequency-Scaling.

The DVFS hardware is controlled through a set of registers referred to
as "FDVFS". They set the target frequency the DVFS hardware should aim
for for each performance domain.

Instead of working around the old binding and its already established
meanings for the reg items, add a new binding. The FDVFS register memory
region is at the beginning, which allows us to easily expand this
binding for future SoCs which may have more than 3 performance domains.

Signed-off-by: Nicolas Frattaroli <[e-mail]>
Reviewed-by: AngeloGioacchino Del Regno <[e-mail]>
Reviewed-by: Rob Herring (Arm) <[e-mail]>
Signed-off-by: Viresh Kumar <[e-mail]>

Documentation/devicetree/bindings/cpufreq/mediatek,mt8196-cpufreq-hw.yaml

···
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/cpufreq/mediatek,mt8196-cpufreq-hw.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: MediaTek Hybrid CPUFreq for MT8196/MT6991 series SoCs
+
+maintainers:
+  - Nicolas Frattaroli <[e-mail]>
+
+description:
+  MT8196 uses CPUFreq management hardware that supports dynamic voltage
+  frequency scaling (dvfs), and can support several performance domains.
+
+properties:
+  compatible:
+    const: mediatek,mt8196-cpufreq-hw
+
+  reg:
+    items:
+      - description: FDVFS control register region
+      - description: OPP tables and control for performance domain 0
+      - description: OPP tables and control for performance domain 1
+      - description: OPP tables and control for performance domain 2
+
+  "#performance-domain-cells":
+    const: 1
+
+required:
+  - compatible
+  - reg
+  - "#performance-domain-cells"
+
+additionalProperties: false
+
+examples:
+  - |
+    cpus {
+            #address-cells = <1>;
+            #size-cells = <0>;
+
+            cpu0: cpu@0 {
+                device_type = "cpu";
+                compatible = "arm,cortex-a720";
+                enable-method = "psci";
+                performance-domains = <&performance 0>;
+                reg = <0x000>;
+            };
+
+            /* ... */
+
+            cpu6: cpu@600 {
+                device_type = "cpu";
+                compatible = "arm,cortex-x4";
+                enable-method = "psci";
+                performance-domains = <&performance 1>;
+                reg = <0x600>;
+            };
+
+            cpu7: cpu@700 {
+                device_type = "cpu";
+                compatible = "arm,cortex-x925";
+                enable-method = "psci";
+                performance-domains = <&performance 2>;
+                reg = <0x700>;
+            };
+    };
+
+    /* ... */
+
+    soc {
+        #address-cells = <2>;
+        #size-cells = <2>;
+
+        performance: performance-controller@c2c2034 {
+            compatible = "mediatek,mt8196-cpufreq-hw";
+            reg = <0 0xc220400 0 0x20>, <0 0xc2c0f20 0 0x120>,
+                  <0 0xc2c1040 0 0x120>, <0 0xc2c1160 0 0x120>;
+            #performance-domain-cells = <1>;
+        };
+    };