mfd: AXP20x: Add bindings documentation

AXP202/AXP209 device tree bindings

The axp20x family current members :

axp202 (X-Powers)

axp209 (X-Powers)

Required properties:

- compatible: "x-powers,axp202" or "x-powers,axp209"

- reg: The I2C slave address for the AXP chip

- interrupt-parent: The parent interrupt controller

- interrupts: SoC NMI / GPIO interrupt connected to the PMIC's IRQ pin

- interrupt-controller: axp20x has its own internal IRQs

- #interrupt-cells: Should be set to 1

Optional properties:

- x-powers,dcdc-freq: defines the work frequency of DC-DC in KHz

		      (range: 750-1875). Default: 1.5MHz

- <input>-supply: a phandle to the regulator supply node. May be omitted if

		  inputs are unregulated, such as using the IPSOUT output

		  from the PMIC.

- regulators: A node that houses a sub-node for each regulator. Regulators

	      not used but preferred to be managed by the OS should be

	      listed as well.

	      See Documentation/devicetree/bindings/regulator/regulator.txt

	      for more information on standard regulator bindings.

Optional properties for DCDC regulators:

- x-powers,dcdc-workmode: 1 for PWM mode, 0 for AUTO (PWM/PFM) mode

			  Default: Current hardware setting

			  The DCDC regulators work in a mixed PWM/PFM mode,

			  using PFM under light loads and switching to PWM

			  for heavier loads. Forcing PWM mode trades efficiency

			  under light loads for lower output noise. This

			  probably makes sense for HiFi audio related

			  applications that aren't battery constrained.

AXP202/AXP209 regulators, type, and corresponding input supply names:

Regulator	  Type		  Supply Name		  Notes

---------	  ----		  -----------		  -----

DCDC2		: DC-DC buck	: vin2-supply

DCDC3		: DC-DC	buck	: vin3-supply

LDO1		: LDO		: acin-supply		: always on

LDO2		: LDO		: ldo24in-supply	: shared supply

LDO3		: LDO		: ldo3in-supply

LDO4		: LDO		: ldo24in-supply	: shared supply

LDO5		: LDO		: ldo5in-supply

Example:

axp209: pmic@34 {

	compatible = "x-powers,axp209";

	reg = <0x34>;

	interrupt-parent = <&nmi_intc>;

	interrupts = <0 IRQ_TYPE_LEVEL_LOW>;

	interrupt-controller;

	#interrupt-cells = <1>;

	regulators {

		x-powers,dcdc-freq = <1500>;

		vdd_cpu: dcdc2 {

			regulator-always-on;

			regulator-min-microvolt = <1000000>;

			regulator-max-microvolt = <1450000>;

			regulator-name = "vdd-cpu";

		};

		vdd_int_dll: dcdc3 {

			regulator-always-on;

			regulator-min-microvolt = <1000000>;

			regulator-max-microvolt = <1400000>;

			regulator-name = "vdd-int-dll";

		};

		vdd_rtc: ldo1 {

			regulator-always-on;

			regulator-min-microvolt = <1200000>;

			regulator-max-microvolt = <1400000>;

			regulator-name = "vdd-rtc";

		};

		avcc: ldo2 {

			regulator-always-on;

			regulator-min-microvolt = <2700000>;

			regulator-max-microvolt = <3300000>;

			regulator-name = "avcc";

		};

		ldo3 {

			/* unused but preferred to be managed by OS */

		};

	};

};