Documentation: mfd: Add binding document for S2MPA01

Added initial binding documentation for S2MPA01 MFD.
Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Acked-by: Mark Brown <broonie@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

Documentation/devicetree/bindings/mfd/s2mpa01.txt

+
+* Samsung S2MPA01 Voltage and Current Regulator
+
+The Samsung S2MPA01 is a multi-function device which includes high
+efficiency buck converters including Dual-Phase buck converter, various LDOs,
+and an RTC. It is interfaced to the host controller using an I2C interface.
+Each sub-block is addressed by the host system using different I2C slave
+addresses.
+
+Required properties:
+- compatible: Should be "samsung,s2mpa01-pmic".
+- reg: Specifies the I2C slave address of the PMIC block. It should be 0x66.
+
+Optional properties:
+- interrupt-parent: Specifies the phandle of the interrupt controller to which
+  the interrupts from s2mpa01 are delivered to.
+- interrupts: An interrupt specifier for the sole interrupt generated by the
+  device.
+
+Optional nodes:
+- regulators: The regulators of s2mpa01 that have to be instantiated should be
+  included in a sub-node named 'regulators'. Regulator nodes and constraints
+  included in this sub-node use the standard regulator bindings which are
+  documented elsewhere.
+
+Properties for BUCK regulator nodes:
+- regulator-ramp-delay: ramp delay in uV/us. May be 6250, 12500
+  (default), 25000, or 50000. May be 0 for disabling the ramp delay on
+  BUCK{1,2,3,4}.
+
+ In the absence of the regulator-ramp-delay property, the default ramp
+ delay will be used.
+
+  NOTE: Some BUCKs share the ramp rate setting i.e. same ramp value will be set
+  for a particular group of BUCKs. So provide same regulator-ramp-delay=<value>.
+
+  The following BUCKs share ramp settings:
+  * 1 and 6
+  * 2 and 4
+  * 8, 9, and 10
+
+The following are the names of the regulators that the s2mpa01 PMIC block
+supports. Note: The 'n' in LDOn and BUCKn represents the LDO or BUCK number
+as per the datasheet of s2mpa01.
+
+	- LDOn
+		  - valid values for n are 1 to 26
+		  - Example: LDO1, LD02, LDO26
+	- BUCKn
+		  - valid values for n are 1 to 10.
+		  - Example: BUCK1, BUCK2, BUCK9
+
+Example:
+
+	s2mpa01_pmic@66 {
+		compatible = "samsung,s2mpa01-pmic";
+		reg = <0x66>;
+
+		regulators {
+			ldo1_reg: LDO1 {
+				regulator-name = "VDD_ALIVE";
+				regulator-min-microvolt = <1000000>;
+				regulator-max-microvolt = <1000000>;
+			};
+
+			ldo2_reg: LDO2 {
+				regulator-name = "VDDQ_MMC2";
+				regulator-min-microvolt = <2800000>;
+				regulator-max-microvolt = <2800000>;
+				regulator-always-on;
+			};
+
+			buck1_reg: BUCK1 {
+				regulator-name = "vdd_mif";
+				regulator-min-microvolt = <950000>;
+				regulator-max-microvolt = <1350000>;
+				regulator-always-on;
+				regulator-boot-on;
+			};
+
+			buck2_reg: BUCK2 {
+				regulator-name = "vdd_arm";
+				regulator-min-microvolt = <950000>;
+				regulator-max-microvolt = <1350000>;
+				regulator-always-on;
+				regulator-boot-on;
+				regulator-ramp-delay = <50000>;
+			};
+		};
+	};