iio: Add binding documentation for imx25 GCQ

Freescale i.MX25 ADC GCQ device

This is a generic conversion queue device that can convert any of the

analog inputs using the ADC unit of the i.MX25.

Required properties:

 - compatible: Should be "fsl,imx25-gcq".

 - reg: Should be the register range of the module.

 - interrupts: Should be the interrupt number of the module.

   Typically this is <1>.

 - interrupt-parent: phandle to the tsadc module of the i.MX25.

 - #address-cells: Should be <1> (setting for the subnodes)

 - #size-cells: Should be <0> (setting for the subnodes)

Optional properties:

 - vref-ext-supply: The regulator supplying the ADC reference voltage.

   Required when at least one subnode uses the this reference.

 - vref-xp-supply: The regulator supplying the ADC reference voltage on pin XP.

   Required when at least one subnode uses this reference.

 - vref-yp-supply: The regulator supplying the ADC reference voltage on pin YP.

   Required when at least one subnode uses this reference.

Sub-nodes:

Optionally you can define subnodes which define the reference voltage

for the analog inputs.

Required properties for subnodes:

 - reg: Should be the number of the analog input.

     0: xp

     1: yp

     2: xn

     3: yn

     4: wiper

     5: inaux0

     6: inaux1

     7: inaux2

Optional properties for subnodes:

 - fsl,adc-refp: specifies the positive reference input as defined in

     <dt-bindings/iio/adc/fsl-imx25-gcq.h>

 - fsl,adc-refn: specifies the negative reference input as defined in

     <dt-bindings/iio/adc/fsl-imx25-gcq.h>

Example:

	adc: adc@50030800 {

		compatible = "fsl,imx25-gcq";

		reg = <0x50030800 0x60>;

		interrupt-parent = <&tscadc>;

		interrupts = <1>;

		#address-cells = <1>;

		#size-cells = <0>;

		inaux@5 {

			reg = <5>;

			fsl,adc-refp = <MX25_ADC_REFP_INT>;

			fsl,adc-refn = <MX25_ADC_REFN_NGND>;

		};

	};

/*

 * This header provides constants for configuring the I.MX25 ADC

 */

#ifndef _DT_BINDINGS_IIO_ADC_FS_IMX25_GCQ_H

#define _DT_BINDINGS_IIO_ADC_FS_IMX25_GCQ_H

#define MX25_ADC_REFP_YP	0 /* YP voltage reference */

#define MX25_ADC_REFP_XP	1 /* XP voltage reference */

#define MX25_ADC_REFP_EXT	2 /* External voltage reference */

#define MX25_ADC_REFP_INT	3 /* Internal voltage reference */

#define MX25_ADC_REFN_XN	0 /* XN ground reference */

#define MX25_ADC_REFN_YN	1 /* YN ground reference */

#define MX25_ADC_REFN_NGND	2 /* Internal ground reference */

#define MX25_ADC_REFN_NGND2	3 /* External ground reference */

#endif