Qualcomm's QPNP PMIC thermal monitor ADC driver (VADC_TM)

QPNP PMIC thermal monitoring (TM) provides interface to thermal clients
to set temperature thresholds and receive notification when the thresholds
are crossed. A 15 bit ADC is used for measurements. The driver is part
of the sysfs thermal framework that provides support to read the trip
points, set threshold for the trip points and enable the trip points.
Seperate kernel api's are provided to usb_id and batt_therm
to set thresholds and receive threshold notifications.

VADC_TM node

Required properties:
- compatible : should be "qcom,qpnp-adc-tm" for thermal ADC driver.
- reg : offset and length of the PMIC Aribter register map.
- address-cells : Must be one.
- size-cells : Must be zero.
- interrupts : The thermal ADC bank peripheral interrupts for eoc, high and low interrupts.
- interrupt-names : Should be "eoc-int-en-set", "high-thr-en-set" and "low-thr-en-set".
- qcom,adc-bit-resolution : Bit resolution of the ADC.
- qcom,adc-vdd-reference : Voltage reference used by the ADC.

Optional properties:
- qcom,thermal-node : If present a thermal node is created and the channel is registered as
		part of the thermal sysfs which allows clients to use the thermal framework
		to set temperature thresholds and receive notification when the temperature
		crosses a set threshold, read temperature and enable/set trip types supported
		by the thermal framework.

Channel nodes
NOTE: Atleast one Channel node is required.

Required properties:
- label : Channel name used for sysfs entry.
- reg : AMUX channel number.
- 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,pre-div-channel-scaling : Pre-div used for the channel before the signal is being measured.
				 Select from the following unsigned int for the corresponding
				 numerator/denominator pre-div ratio.
				 0 : pre-div ratio of {1, 1}
				 1 : pre-div ratio of {1, 3}
				 2 : pre-div ratio of {1, 4}
				 3 : pre-div ratio of {1, 6}
				 4 : pre-div ratio of {1, 20}
- qcom,calibration-type : Reference voltage to use for channel calibration.
			  Channel calibration is dependendent on the channel.
			  Certain channels like XO_THERM, BATT_THERM use ratiometric
			  calibration. Most other channels fall under absolute calibration.
			  Select from the following strings.
			  "absolute" : Uses the 625mv and 1.25V reference channels.
			  "ratiometric" : Uses the reference Voltage/GND for calibration.
- qcom,scale-function : Scaling fuction used to convert raw ADC code to units specific to
			a given channel.
			Select from the following unsigned int.
			0 : Default scaling to convert raw adc code to voltage.
			1 : Conversion to temperature based on btm parameters.
			2 : Returns result in milli degree's Centigrade.
			3 : Returns current across 0.1 ohm resistor.
			4 : Returns XO thermistor voltage in degree's Centigrade.
- qcom,hw-settle-time : Settling period for the channel before ADC read.
			Select from the following unsigned int.
			0 : 0us
			1 : 100us
			2 : 200us
			3 : 300us
			4 : 400us
			5 : 500us
			6 : 600us
			7 : 700us
			8 : 800us
			9 : 900us
			0xa : 1ms
			0xb : 2ms
			0xc : 4ms
			0xd : 6ms
			0xe : 8ms
			0xf : 10ms
- 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
			0 : 1
			1 : 2
			2 : 4
			3 : 8
			4 : 16
			5 : 32
			6 : 64
			7 : 128
			8 : 256
- qcom,btm-channel-number : There are 5 BTM channels. The BTM channel numbers are statically
			    allocated to the corresponding channel node.

Example:
	/* Main Node */
	qcom,vadc@3400 {
                        compatible = "qcom,qpnp-adc-tm";
                        reg = <0x3400 0x100>;
			#address-cells = <1>;
			#size-cells = <0>;
                        interrupts = <0x0 0x34 0x0>,
					<0x0 0x34 0x3>,
					<0x0 0x34 0x4>;
			interrupt-names = "eoc-int-en-set",
					  "high-thr-en-set",
					  "low-thr-en-set";
                        qcom,adc-bit-resolution = <15>;
                        qcom,adc-vdd-reference = <1800>;

			/* Channel Node to be registered as part of thermal sysfs */
                        chan@b5 {
                                label = "pa_therm1";
				reg = <0xb5>;
                                qcom,decimation = <0>;
                                qcom,pre-div-channel-scaling = <0>;
                                qcom,calibration-type = "absolute";
                                qcom,scale-function = <2>;
                                qcom,hw-settle-time = <0>;
                                qcom,fast-avg-setup = <0>;
				qcom,btm-channel-number = <0x70>;
				qcom,thermal-node;
                        };

			/* Channel Node */
			chan@6 {
				label = "vbat_sns";
				reg = <6>;
				qcom,decimation = <0>;
				qcom,pre-div-channel-scaling = <1>;
				qcom,calibration-type = "absolute";
				qcom,scale-function = <3>;
				qcom,hw-settle-time = <0>;
				qcom,fast-avg-setup = <0>;
				qcom,btm-channel-number = <0x78>;
			};
	};