Qualcomm's QPNP PMIC current ADC driver

QPNP PMIC current ADC (IADC) provides interface to clients to read
current. A 16 bit ADC is used for current measurements. There are multiple
peripherals to the IADC and the scope of the driver is to provide interface
for the USR peripheral of the IADC.

IADC node

Required properties:
- compatible : should be "qcom,qpnp-iadc" for Current ADC driver.
- reg : offset and length of the PMIC Arbiter register map.
- reg-names : resource names used for the physical base address of the PMIC IADC
	      peripheral, the SMBB_BAT_IF_TRIM_CNST_RDS register.
	      Should be "iadc-base" for the PMIC IADC peripheral base register.
	      Should be "batt-id-trim-cnst-rds" for reading the
	      SMBB_BAT_IF_TRIM_CNST_RDS register.
- address-cells : Must be one.
- size-cells : Must be zero.
- interrupts : The USR bank peripheral IADC interrupt.
- interrupt-names : Should contain "eoc-int-en-set".
- qcom,adc-bit-resolution : Bit resolution of the ADC.
- qcom,adc-vdd-reference : Voltage reference used by the ADC.

Optional properties:
- qcom,rsense : Use this property when external rsense should be used
		for current calculation and specify the units in nano-ohms.
- qcom,iadc-poll-eoc: Use polling instead of interrupts for End of Conversion completion.
- qcom,pmic-revid : Phandle pointing to the revision peripheral node. Use it to query the
		    PMIC type and revision for applying the appropriate temperature
		    compensation parameters.
- qcom,use-default-rds-trim : Add this property to check if certain conditions are to be checked
			      reading the SMBB_BAT_IF_CNST_RDS, IADC_RDS trim register and
			      manufacturer type. Check the driver for conditions that each of the type.
			      0 : Select the TypeA to read the IADC and SMBB trim register and
				  apply the default RSENSE if conditions are met.
			      1 : Select the TypeB to read the IADC, SMBB trim register and
				  manufacturer type and apply the default RSENSE if conditions are met.
			      2 : Select the TypeC to read the IADC, SMBB trim register and
				  apply the default RSENSE if conditions are met.

Channel node
NOTE: Atleast one Channel node is required.

Client required property:
- qcom,<consumer name>-iadc : The phandle to the corresponding iadc device.
			The consumer name passed to the driver when calling
			qpnp_get_iadc() is used to associate the client
			with the corresponding device.

Required properties:
- label : Channel name used for sysfs entry.
- reg : AMUX channel number.
- qcom,channel-num : Channel number associated to the AMUX input.
- qcom,decimation : Sampling rate to use for the individual channel measurement.
		    Select from the following unsigned int.
		    0 : 512
		    1 : 1K
		    2 : 2K
		    3 : 4K
- qcom,fast-avg-setup : Average number of samples to be used for measurement. Fast averaging
			provides the option to obtain a single measurement from the ADC that
			is an average of multiple samples. The value selected is 2^(value)
			Select from the following unsigned int.
			0 : 1
			1 : 2
			2 : 4
			3 : 8
			4 : 16
			5 : 32
			6 : 64
			7 : 128
			8 : 256
- qcom,iadc-vadc : Corresponding phandle of the VADC device to read the die_temperature and set
		simultaneous voltage and current conversion requests.

Example:
	/* Main Node */
	qcom,iadc@3200 {
                        compatible = "qcom,qpnp-iadc";
                        reg = <0x3200 0x100>;
			#address-cells = <1>;
			#size-cells = <0>;
                        interrupts = <0 0x36 0>;
			interrupt-names = "eoc-int-en-set";
                        qcom,adc-bit-resolution = <16>;
                        qcom,adc-vdd-reference = <1800>;
			qcom,rsense = <1500>;
			qcom,iadc-vadc = <&pm8941_vadc>;

			/* Channel Node */
                        chan@0 = {
                                label = "rsense";
                                reg = <0>;
                                qcom,decimation = <0>;
                                qcom,fast-avg-setup = <0>;
                        };
	};

Client device example:
/* Add to the clients node that needs the IADC */
client_node {
	qcom,client-iadc = <&pm8941_iadc>;
};