PM / devfreq: event: Add documentation for exynos-ppmu devfreq-event driver

This patch adds the documentation for Exynos PPMU (Platform Performance
Monitoring Unit) devfreq-event driver.

Cc: MyungJoo Ham <[e-mail]>
Cc: Kyungmin Park <[e-mail]>
Signed-off-by: Chanwoo Choi <[e-mail]>
Signed-off-by: MyungJoo Ham <[e-mail]>

Documentation/devicetree/bindings/devfreq/event/exynos-ppmu.txt

···
+
+* Samsung Exynos PPMU (Platform Performance Monitoring Unit) device
+
+The Samsung Exynos SoC has PPMU (Platform Performance Monitoring Unit) for
+each IP. PPMU provides the primitive values to get performance data. These
+PPMU events provide information of the SoC's behaviors so that you may
+use to analyze system performance, to make behaviors visible and to count
+usages of each IP (DMC, CPU, RIGHTBUS, LEFTBUS, CAM interface, LCD, G3D, MFC).
+The Exynos PPMU driver uses the devfreq-event class to provide event data
+to various devfreq devices. The devfreq devices would use the event data when
+derterming the current state of each IP.
+
+Required properties:
+- compatible: Should be "samsung,exynos-ppmu".
+- reg: physical base address of each PPMU and length of memory mapped region.
+
+Optional properties:
+- clock-names : the name of clock used by the PPMU, "ppmu"
+- clocks : phandles for clock specified in "clock-names" property
+- #clock-cells: should be 1.
+
+Example1 : PPMU nodes in exynos3250.dtsi are listed below.
+
+		ppmu_dmc0: ppmu_dmc0@106a0000 {
+			compatible = "samsung,exynos-ppmu";
+			reg = <0x106a0000 0x2000>;
+			status = "disabled";
+		};
+
+		ppmu_dmc1: ppmu_dmc1@106b0000 {
+			compatible = "samsung,exynos-ppmu";
+			reg = <0x106b0000 0x2000>;
+			status = "disabled";
+		};
+
+		ppmu_cpu: ppmu_cpu@106c0000 {
+			compatible = "samsung,exynos-ppmu";
+			reg = <0x106c0000 0x2000>;
+			status = "disabled";
+		};
+
+		ppmu_rightbus: ppmu_rightbus@112a0000 {
+			compatible = "samsung,exynos-ppmu";
+			reg = <0x112a0000 0x2000>;
+			clocks = <&cmu CLK_PPMURIGHT>;
+			clock-names = "ppmu";
+			status = "disabled";
+		};
+
+		ppmu_leftbus: ppmu_leftbus0@116a0000 {
+			compatible = "samsung,exynos-ppmu";
+			reg = <0x116a0000 0x2000>;
+			clocks = <&cmu CLK_PPMULEFT>;
+			clock-names = "ppmu";
+			status = "disabled";
+		};
+
+Example2 : Events of each PPMU node in exynos3250-rinato.dts are listed below.
+
+	&ppmu_dmc0 {
+		status = "okay";
+
+		events {
+			ppmu_dmc0_3: ppmu-event3-dmc0 {
+				event-name = "ppmu-event3-dmc0";
+			};
+
+			ppmu_dmc0_2: ppmu-event2-dmc0 {
+				event-name = "ppmu-event2-dmc0";
+			};
+
+			ppmu_dmc0_1: ppmu-event1-dmc0 {
+				event-name = "ppmu-event1-dmc0";
+			};
+
+			ppmu_dmc0_0: ppmu-event0-dmc0 {
+				event-name = "ppmu-event0-dmc0";
+			};
+		};
+	};
+
+	&ppmu_dmc1 {
+		status = "okay";
+
+		events {
+			ppmu_dmc1_3: ppmu-event3-dmc1 {
+				event-name = "ppmu-event3-dmc1";
+			};
+		};
+	};
+
+	&ppmu_leftbus {
+		status = "okay";
+
+		events {
+			ppmu_leftbus_3: ppmu-event3-leftbus {
+				event-name = "ppmu-event3-leftbus";
+			};
+		};
+	};
+
+	&ppmu_rightbus {
+		status = "okay";
+
+		events {
+			ppmu_rightbus_3: ppmu-event3-rightbus {
+				event-name = "ppmu-event3-rightbus";
+			};
+		};
+	};