Re: Using a GPIO as an interrupt line

On Tue, Nov 19, 2019 at 10:28:15AM +0100, Marc Gonzalez wrote:

Hello,

The board I'm working on provides a TCA9539 I/O expander.
Or, as the datasheet(*) calls it, a "Low Voltage 16-Bit I2C and
SMBus Low-Power I/O Expander with Interrupt Output, Reset Pin,
and Configuration Registers"

(*) http://www.ti.com/lit/ds/symlink/tca9539.pdf

The binding is documented in Documentation/devicetree/bindings/gpio/gpio-pca953x.txt

I have some doubts about the interrupt output, described as:

Optional properties:
 - interrupts: interrupt specifier for the device's interrupt output.

In my board's DT, the I/O expander is described as:

	exp1: gpio@74 {
		compatible = "ti,tca9539";
		reg = <0x74>;
		gpio-controller;
		#gpio-cells = <2>;
		reset-gpios = <&tlmm 96 GPIO_ACTIVE_LOW>;
		pinctrl-names = "default";
		pinctrl-0 = <&top_exp_rst>;
		interrupt-parent = <&tlmm>;
		interrupts = <42 IRQ_TYPE_LEVEL_HIGH>;

This specifies an interrupt signal, number 42, on the tlmm interrupt
controller. It isn't a GPIO specification. Not every interrupt is a
GPIO, and some SoCs can have dedicated interrupt pins that are
exactly that.

Hence, needlessly limiting an external device to requiring a GPIO for
its interrupt is detrimental.

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