OPP: Introduce "required-opp" property

Devices have inter-dependencies some times. For example a device that
needs to run at 800 MHz, needs another device (e.g. Its power domain) to
be configured at a particular operating performance point.

This patch introduces a new property "required-opp" which can be present
directly in a device's node (if it doesn't need to change its OPPs), or
in device's OPP nodes. More details on the property can be seen in the
binding itself.

Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

Documentation/devicetree/bindings/opp/opp.txt

@@ -159,6 +159,14 @@ Optional properties:
 
 - status: Marks the node enabled/disabled.
 
+- required-opp: This contains phandle to an OPP node in another device's OPP
+  table. It may contain an array of phandles, where each phandle points to an
+  OPP of a different device. It should not contain multiple phandles to the OPP
+  nodes in the same OPP table. This specifies the minimum required OPP of the
+  device(s), whose OPP's phandle is present in this property, for the
+  functioning of the current device at the current OPP (where this property is
+  present).
+
 Example 1: Single cluster Dual-core ARM cortex A9, switch DVFS states together.
 
 / {

Documentation/devicetree/bindings/power/power_domain.txt

@@ -126,4 +126,63 @@ The node above defines a typical PM domain consumer device, which is located
 inside a PM domain with index 0 of a power controller represented by a node
 with the label "power".
 
+Optional properties:
+- required-opp: This contains phandle to an OPP node in another device's OPP
+  table. It may contain an array of phandles, where each phandle points to an
+  OPP of a different device. It should not contain multiple phandles to the OPP
+  nodes in the same OPP table. This specifies the minimum required OPP of the
+  device(s), whose OPP's phandle is present in this property, for the
+  functioning of the current device at the current OPP (where this property is
+  present).
+
+Example:
+- OPP table for domain provider that provides two domains.
+
+	domain0_opp_table: opp-table0 {
+		compatible = "operating-points-v2";
+
+		domain0_opp_0: opp-1000000000 {
+			opp-hz = /bits/ 64 <1000000000>;
+			opp-microvolt = <975000 970000 985000>;
+		};
+		domain0_opp_1: opp-1100000000 {
+			opp-hz = /bits/ 64 <1100000000>;
+			opp-microvolt = <1000000 980000 1010000>;
+		};
+	};
+
+	domain1_opp_table: opp-table1 {
+		compatible = "operating-points-v2";
+
+		domain1_opp_0: opp-1200000000 {
+			opp-hz = /bits/ 64 <1200000000>;
+			opp-microvolt = <975000 970000 985000>;
+		};
+		domain1_opp_1: opp-1300000000 {
+			opp-hz = /bits/ 64 <1300000000>;
+			opp-microvolt = <1000000 980000 1010000>;
+		};
+	};
+
+	power: power-controller@12340000 {
+		compatible = "foo,power-controller";
+		reg = <0x12340000 0x1000>;
+		#power-domain-cells = <1>;
+		operating-points-v2 = <&domain0_opp_table>, <&domain1_opp_table>;
+	};
+
+	leaky-device0@12350000 {
+		compatible = "foo,i-leak-current";
+		reg = <0x12350000 0x1000>;
+		power-domains = <&power 0>;
+		required-opp = <&domain0_opp_0>;
+	};
+
+	leaky-device1@12350000 {
+		compatible = "foo,i-leak-current";
+		reg = <0x12350000 0x1000>;
+		power-domains = <&power 1>;
+		required-opp = <&domain1_opp_1>;
+	};
+
 [1]. Documentation/devicetree/bindings/power/domain-idle-state.txt