* Maxim/Dallas Semiconductor DS-1302 RTC

Simple device which could be used to store date/time between reboots.

The device uses the standard MicroWire half-duplex transfer timing.
Master output is set on low clock and sensed by the RTC on the rising
edge. Master input is set by the RTC on the trailing edge and is sensed
by the master on low clock.

Required properties:

- compatible : Should be "maxim,ds1302"

Required SPI properties:

- reg : Should be address of the device chip select within
  the controller.

- spi-max-frequency : DS-1302 has 500 kHz if powered at 2.2V,
  and 2MHz if powered at 5V.

- spi-3wire : The device has a shared signal IN/OUT line.

- spi-lsb-first : DS-1302 requires least significant bit first
  transfers.

- spi-cs-high: DS-1302 has active high chip select line. This is
  required unless inverted in hardware.

Example:

spi@901c {
	#address-cells = <1>;
	#size-cells = <0>;
	compatible = "icpdas,lp8841-spi-rtc";
	reg = <0x901c 0x1>;

	rtc@0 {
		compatible = "maxim,ds1302";
		reg = <0>;
		spi-max-frequency = <500000>;
		spi-3wire;
		spi-lsb-first;
		spi-cs-high;
	};
};