Texas Instruments OMAP compatible OPP supply description

OMAP5, DRA7, and AM57 family of SoCs have Class0 AVS eFuse registers which
contain data that can be used to adjust voltages programmed for some of their
supplies for more efficient operation. This binding provides the information
needed to read these values and use them to program the main regulator during
an OPP transitions.

Also, some supplies may have an associated vbb-supply which is an Adaptive Body
Bias regulator which much be transitioned in a specific sequence with regards
to the vdd-supply and clk when making an OPP transition. By supplying two
regulators to the device that will undergo OPP transitions we can make use
of the multi regulator binding that is part of the OPP core described here [1]
to describe both regulators needed by the platform.

[1] Documentation/devicetree/bindings/opp/opp-v2.yaml

Required Properties for Device Node:
- vdd-supply: phandle to regulator controlling VDD supply
- vbb-supply: phandle to regulator controlling Body Bias supply
	      (Usually Adaptive Body Bias regulator)

Required Properties for opp-supply node:
- compatible: Should be one of:
	"ti,omap-opp-supply" - basic OPP supply controlling VDD and VBB
	"ti,omap5-opp-supply" - OMAP5+ optimized voltages in efuse(class0)VDD
			    along with VBB
	"ti,omap5-core-opp-supply" - OMAP5+ optimized voltages in efuse(class0) VDD
			    but no VBB.
- reg: Address and length of the efuse register set for the device (mandatory
	only for "ti,omap5-opp-supply")
- ti,efuse-settings: An array of u32 tuple items providing information about
	optimized efuse configuration. Each item consists of the following:
	volt: voltage in uV - reference voltage (OPP voltage)
	efuse_offseet: efuse offset from reg where the optimized voltage is stored.
- ti,absolute-max-voltage-uv: absolute maximum voltage for the OPP supply.

Example:

/* Device Node (CPU)  */
cpus {
	cpu0: cpu@0 {
		device_type = "cpu";

		...

		vdd-supply = <&vcc>;
		vbb-supply = <&abb_mpu>;
	};
};

/* OMAP OPP Supply with Class0 registers */
opp_supply_mpu: opp_supply@4a003b20 {
	compatible = "ti,omap5-opp-supply";
	reg = <0x4a003b20 0x8>;
	ti,efuse-settings = <
	/* uV   offset */
	1060000 0x0
	1160000 0x4
	1210000 0x8
	>;
	ti,absolute-max-voltage-uv = <1500000>;
};