Qualcomm QPNP BSI - battery serial interface devices

qpnp-bsi is a BIF driver which supports the BSI peripheral inside of PMICs
that utilize the MSM SPMI implementation.

Required properties:
- compatible:      Must be "qcom,qpnp-bsi".
- reg:             Specifies the SPMI address and size for this BSI device as
                    well as the address of the BATT_ID status register.
- reg-names:       A list of strings identifying the reg property entries.  The
                    list must contain both "bsi-base" and "batt-id-status".
- label:           A string used as a descriptive name for this BIF controller.
- interrupts:      Specifies a list of four interrupts corresponding to
                    IRQ ERR, IRQ RX, IRQ TX, and IRQ BATT_PRESENT in any order.
- interrupt-names: Must be a list of strings containing all three of these
                    strings: "err", "rx", "tx", "batt-present".  The ordering of
                    these strings must match the ordering of the interrupts in
                    the "interrupts" property.

Required structure:
- A qcom,qpnp-bsi node must be a child of an SPMI node that has specified the
	spmi-slave-container property.

Optional properties:
- qcom,min-clock-period:  This property specifies a minimum clock period for the
                           Tau BIF reference in nanoseconds.  It can be used to
                           impose a minimum period which is higher (i.e. more
                           restrictive) than that supported by the hardware.
                           The BSI module supports 8 possible periods between
                           2080 ns and 150420 ns.
- qcom,max-clock-period:  This property specifies a maximum clock period for the
                           Tau BIF reference in nanoseconds.  It can be used to
                           impose a maximum period which is lower (i.e. more
                           restrictive) than that supported by the hardware.
                           The BSI module supports 8 possible periods between
                           2080 ns and 150420 ns.
- qcom,sample-rate:       Specifies the rate at which the BIF BCL should be
                           sampled during communication with respect to the Tau
                           BIF reference rate.  Supported values are 4 and 8
                           which represent 4x and 8x sampling rates
                           respectively.  If this property is not specified,
                           then 4x sampling is assumed.
- qcom,channel-num:       VADC channel number associated PMIC BATT_ID pin.  If
                           no channel is specified, then it will not be
                           possible to measure the slave Rid.
- qcom,pullup-ohms:       Host side pull-up resistance present on BCL in ohms.
                           If no value is specified, then 100000 ohms is
                           assumed.
- qcom,vref-microvolts:   Reference voltage used for BCL divider circuit in
                           microvolts.  If no value is specified, then
                           1800000 uV is assumed.
- qcom,bsi-vadc:	  Corresponding VADC device phandle.

All properties specified within for the BIF framework can also be used. These
properties can be found in bif.txt.

Example:
	qcom,spmi@fc4c0000 {
		#address-cells = <1>;
		#size-cells = <0>;
		interrupt-controller;
		#interrupt-cells = <3>;

		qcom,pm8941@1 {
			spmi-slave-container;
			reg = <0x1>;
			#address-cells = <1>;
			#size-cells = <1>;

			qcom,bsi@1b00 {
				compatible = "qcom,qpnp-bsi";
				reg = <0x1b00 0x100>,
				      <0x1208 0x1>;
				reg-names = "bsi-base", "batt-id-status";
				label = "pm8941-bsi";
				interrupts = <0x0 0x1b 0x0>,
					     <0x0 0x1b 0x1>,
					     <0x0 0x1b 0x2>,
					     <0x0 0x12 0x0>;
				interrupt-names = "err",
						  "rx",
						  "tx",
						  "batt-present";
				qcom,sample-rate = <8>;
				qcom,min-clock-period = <15830>;
				qcom,max-clock-period = <122080>;
				qcom,channel-num = <0x31>;
				qcom,pullup-ohms = <100000>;
				qcom,vref-microvolts = <1800000>;
				qcom,bsi-vadc = <&pm8941_vadc>;
			};
		};
	};