dt-bindings: gpio: Add Spreadtrum EIC controller documentation

Spreadtrum EIC controller bindings

The EIC is the abbreviation of external interrupt controller, which can

be used only in input mode. The Spreadtrum platform has 2 EIC controllers,

one is in digital chip, and another one is in PMIC. The digital chip EIC

controller contains 4 sub-modules: EIC-debounce, EIC-latch, EIC-async and

EIC-sync. But the PMIC EIC controller contains only one EIC-debounce sub-

module.

The EIC-debounce sub-module provides up to 8 source input signal

connections. A debounce mechanism is used to capture the input signals'

stable status (millisecond resolution) and a single-trigger mechanism

is introduced into this sub-module to enhance the input event detection

reliability. In addition, this sub-module's clock can be shut off

automatically to reduce power dissipation. Moreover the debounce range

is from 1ms to 4s with a step size of 1ms. The input signal will be

ignored if it is asserted for less than 1 ms.

The EIC-latch sub-module is used to latch some special power down signals

and generate interrupts, since the EIC-latch does not depend on the APB

clock to capture signals.

The EIC-async sub-module uses a 32kHz clock to capture the short signals

(microsecond resolution) to generate interrupts by level or edge trigger.

The EIC-sync is similar with GPIO's input function, which is a synchronized

signal input register. It can generate interrupts by level or edge trigger

when detecting input signals.

Required properties:

- compatible: Should be one of the following:

  "sprd,sc9860-eic-debounce",

  "sprd,sc9860-eic-latch",

  "sprd,sc9860-eic-async",

  "sprd,sc9860-eic-sync",

  "sprd,sc27xx-eic".

- reg: Define the base and range of the I/O address space containing

  the GPIO controller registers.

- gpio-controller: Marks the device node as a GPIO controller.

- #gpio-cells: Should be <2>. The first cell is the gpio number and

  the second cell is used to specify optional parameters.

- interrupt-controller: Marks the device node as an interrupt controller.

- #interrupt-cells: Should be <2>. Specifies the number of cells needed

  to encode interrupt source.

- interrupts: Should be the port interrupt shared by all the gpios.

Example:

	eic_debounce: gpio@40210000 {

		compatible = "sprd,sc9860-eic-debounce";

		reg = <0 0x40210000 0 0x80>;

		gpio-controller;

		#gpio-cells = <2>;

		interrupt-controller;

		#interrupt-cells = <2>;

		interrupts = <GIC_SPI 52 IRQ_TYPE_LEVEL_HIGH>;

	};

	eic_latch: gpio@40210080 {

		compatible = "sprd,sc9860-eic-latch";

		reg = <0 0x40210080 0 0x20>;

		gpio-controller;

		#gpio-cells = <2>;

		interrupt-controller;

		#interrupt-cells = <2>;

		interrupts = <GIC_SPI 52 IRQ_TYPE_LEVEL_HIGH>;

	};

	eic_async: gpio@402100a0 {

		compatible = "sprd,sc9860-eic-async";

		reg = <0 0x402100a0 0 0x20>;

		gpio-controller;

		#gpio-cells = <2>;

		interrupt-controller;

		#interrupt-cells = <2>;

		interrupts = <GIC_SPI 52 IRQ_TYPE_LEVEL_HIGH>;

	};

	eic_sync: gpio@402100c0 {

		compatible = "sprd,sc9860-eic-sync";

		reg = <0 0x402100c0 0 0x20>;

		gpio-controller;

		#gpio-cells = <2>;

		interrupt-controller;

		#interrupt-cells = <2>;

		interrupts = <GIC_SPI 52 IRQ_TYPE_LEVEL_HIGH>;

	};

	pmic_eic: gpio@300 {

		compatible = "sprd,sc27xx-eic";

		reg = <0x300>;

		interrupt-parent = <&sc2731_pmic>;

		interrupts = <5 IRQ_TYPE_LEVEL_HIGH>;

		gpio-controller;

		#gpio-cells = <2>;

		interrupt-controller;

		#interrupt-cells = <2>;

	};