Summit SMB137C Battery Charger

The SMB137C is controlled via an I2C bus.  Its 7-bit I2C slave address is
programmed during manufacturing.

Required properties:
- compatible:		Must be "summit,smb137c".
- reg:			The device's 7-bit I2C address.

Optional properties:
- summit,chg-current-ma		Maximum battery charging current in milliamps.
				Supported values are: 500, 650, 750, 850, 950,
				1100, 1300, and 1500.
- summit,term-current-ma	Charging terminaton current in milliamps.
				Supported values are: 0, 35, 50, 100, and 150.
				A value of 0 means no termination current is
				used.
- summit,pre-chg-current-ma	Maximum battery pre-charging current in
				milliamps.  This current limit is applied while
				the battery voltage is below the pre-charge /
				fast-charge threshold.  Supported values are:
				50, 100, 150, and 200.
- summit,float-voltage-mv	Battery voltage threshold in millivolts at which
				point charging switches from constant current to
				constant voltage.  Supported values are: 3460 up
				through 4730 in 10 mV steps.
- summit,thresh-voltage-mv	Threshold voltage in millivolts which is used to
				switch between pre-charge and fast-charge
				current limits.  Supported values are: 2400 up
				to 3100 in 100 mV steps.
- summit,recharge-thresh-mv	Specifies the minimum voltage drop in millivolts
				below the float voltage that is required in
				order to initiate a new charging cycle.
				Supported values are: 75 and 120.
- summit,system-voltage-mv	Regulated voltage output on the VOUTL pin in
				millivolts.  Supported values are 4250 and 4460.
- summit,charging-timeout	Maximum duration in minutes that a single charge
				cycle may last.  Supported values are: 0, 382,
				764, and 1527.  A value of 0 means that no
				charge cycle timeout is used and charging can
				continue indefinitely.
- summit,pre-charge-timeout	Maximum time in minutes spent in the pre-charge
				state in any given charge cycle.  Supports
				values are: 0, 48, 95, and 191.  A value of 0
				means that there is no limit to the amount of
				time that may be spent in the pre-charge state.
- summit,therm-current-ua	Thermistor current in microamps to be used for
				battery temperature monitoring.  Supported
				values are 10, 20, 40, and 100.  These values
				correspond to 100, 50, 25, and 10 kohm NTC
				thermistors respectively.
- summit,temperature-min	Specifies the minimum temperature at which
				charging is allowed.  Supported values are
				0 to 7.  These values correspond to -20 C to
				+15 C in 5 C increments for an NTC thermistor
				with beta = 4400.
- summit,temperature-max	Specifies the maximum temperature at which
				charging is allowed.  Supported values are
				0 to 7.  These values correspond to +30 C to
				+65 C in 5 C increments for an NTC thermistor
				with beta = 4400.

Note: If an optional property is not specified, then the hardware default value
will be used.

Example:
/ {
	i2c@f9925000 {
		charger@57 {
			compatible = "summit,smb137c";
			reg = <0x57>;
			summit,chg-current-ma = <1500>;
			summit,term-current-ma = <50>;
			summit,pre-chg-current-ma = <100>;
			summit,float-voltage-mv = <4200>;
			summit,thresh-voltage-mv = <3000>;
			summit,recharge-thresh-mv = <75>;
			summit,system-voltage-mv = <4250>;
			summit,charging-timeout = <382>;
			summit,pre-charge-timeout = <48>;
			summit,therm-current-ua = <10>;
			summit,temperature-min = <4>; /*  0 C */
			summit,temperature-max = <3>; /* 45 C */
		};
	};
};