* Renesas RCar GyroADC device driver

The GyroADC block is a reduced SPI block with up to 8 chipselect lines,
which supports the SPI protocol of a selected few SPI ADCs. The SPI ADCs
are sampled by the GyroADC block in a round-robin fashion and the result
presented in the GyroADC registers.

Required properties:
- compatible:	Should be "<soc-specific>", "renesas,rcar-gyroadc".
                The <soc-specific> should be one of:
		renesas,r8a7791-gyroadc - for the GyroADC block present
					  in r8a7791 SoC
		renesas,r8a7792-gyroadc - for the GyroADC with interrupt
					  block present in r8a7792 SoC
- reg:		Address and length of the register set for the device
- clocks:	References to all the clocks specified in the clock-names
		property as specified in
		Documentation/devicetree/bindings/clock/clock-bindings.txt.
- clock-names:	Shall contain "fck" and "if". The "fck" is the GyroADC block
		clock, the "if" is the interface clock.
- power-domains: Must contain a reference to the PM domain, if available.
- #address-cells: Should be <1> (setting for the subnodes) for all ADCs
		except for "fujitsu,mb88101a". Should be <0> (setting for
		only subnode) for "fujitsu,mb88101a".
- #size-cells:	Should be <0> (setting for the subnodes)

Sub-nodes:
You must define subnode(s) which select the connected ADC type and reference
voltage for the GyroADC channels.

Required properties for subnodes:
- compatible:	Should be either of:
		"fujitsu,mb88101a"
			- Fujitsu MB88101A compatible mode,
			  12bit sampling, up to 4 channels can be sampled in
			  round-robin fashion. One Fujitsu chip supplies four
			  GyroADC channels with data as it contains four ADCs
			  on the chip and thus for 4-channel operation, single
			  MB88101A is required. The Cx chipselect lines of the
			  MB88101A connect directly to two CHS lines of the
			  GyroADC, no demuxer is required. The data out line
			  of each MB88101A connects to a shared input pin of
			  the GyroADC.
		"ti,adcs7476" or "ti,adc121" or "adi,ad7476"
			- TI ADCS7476 / TI ADC121 / ADI AD7476 compatible mode,
			  15bit sampling, up to 8 channels can be sampled in
			  round-robin fashion. One TI/ADI chip supplies single
			  ADC channel with data, thus for 8-channel operation,
			  8 chips are required. A 3:8 chipselect demuxer is
			  required to connect the nCS line of the TI/ADI chips
			  to the GyroADC, while MISO line of each TI/ADI ADC
			  connects to a shared input pin of the GyroADC.
		"maxim,max1162" or "maxim,max11100"
			- Maxim MAX1162 / Maxim MAX11100 compatible mode,
			  16bit sampling, up to 8 channels can be sampled in
			  round-robin fashion. One Maxim chip supplies single
			  ADC channel with data, thus for 8-channel operation,
			  8 chips are required. A 3:8 chipselect demuxer is
			  required to connect the nCS line of the MAX chips
			  to the GyroADC, while MISO line of each Maxim ADC
			  connects to a shared input pin of the GyroADC.
- reg:		Should be the number of the analog input. Should be present
		for all ADCs except "fujitsu,mb88101a".
- vref-supply:	Reference to the channel reference voltage regulator.

Example:
	vref_max1162: regulator-vref-max1162 {
		compatible = "regulator-fixed";

		regulator-name = "MAX1162 Vref";
		regulator-min-microvolt = <4096000>;
		regulator-max-microvolt = <4096000>;
	};

	adc@e6e54000 {
		compatible = "renesas,r8a7791-gyroadc", "renesas,rcar-gyroadc";
		reg = <0 0xe6e54000 0 64>;
		clocks = <&mstp9_clks R8A7791_CLK_GYROADC>, <&clk_65m>;
		clock-names = "fck", "if";
		power-domains = <&sysc R8A7791_PD_ALWAYS_ON>;

		pinctrl-0 = <&adc_pins>;
		pinctrl-names = "default";

		#address-cells = <1>;
		#size-cells = <0>;

		adc@0 {
			reg = <0>;
			compatible = "maxim,max1162";
			vref-supply = <&vref_max1162>;
		};

		adc@1 {
			reg = <1>;
			compatible = "maxim,max1162";
			vref-supply = <&vref_max1162>;
		};
	};