How to use a gpio as an interrupt?

Question

I am looking for how to use a gpio as an interrupt using device tree dts file.

previously I did that by using the following code in my dts file

                interrupts = <3 30>;
                #interrupt-cells = <2>;
                interrupt-parent = <&intc>;

where intc is

                intc: interrupt-controller {
                compatible = "brcm,bcm2708-armctrl-ic";
                reg = <0x7e00b200 0x200>;
                interrupt-controller;
                #interrupt-cells = <2>;
                };

But now in 3.18.5 everything changed in the kernel of the rpi, now we need to use the gpio to do the same that we did earlier.

But I stucked in middle of it.

The gpio code is

        gpio: gpio {
        compatible = "brcm,bcm2835-gpio";
        reg = <0x7e200000 0xb4>;
        interrupts = <2 17>, <2 18>;

        gpio-controller;
        #gpio-cells = <2>;

        interrupt-controller;
        #interrupt-cells = <2>;
        };

I need to use this gpio node as my interrupt controller.

How can I do that? How to specify which gpio is to be used as the interrupt? Any suggestions are welcome

Answer 1

Are you trying to get interrupts for output gpio ?

Maybe this will help: https://github.com/raspberrypi/linux/issues/808

It seems the gpios with kernel 3.18.5 are a bit unstable, maybe waiting for patches to come is a good idea.

Otherwise, with default DTS the gpio pins are attached to the gpio controller and should benefit from the interrupt controller.

Extracted from 3.18.y pi kernel dts : https://github.com/raspberrypi/linux/blob/rpi-3.18.y/arch/arm/boot/dts/bcm2835-rpi-b.dts

&gpio {
   pinctrl-names = "default";
   pinctrl-0 = <&gpioout &alt0 &alt2 &alt3>;
   gpioout: gpioout {
      brcm,pins = <6>;
      brcm,function = <1>; /* GPIO out */
   };
   alt0: alt0 {
      brcm,pins = <0 1 2 3 4 5 7 8 9 10 11 14 15 40 45>;
      brcm,function = <4>; /* alt0 */
   };
   alt3: alt3 {
      brcm,pins = <48 49 50 51 52 53>;
      brcm,function = <7>; /* alt3 */
   };
   /* I2S interface */
   alt2: alt2 {
      brcm,pins = <28 29 30 31>;
      brcm,function = <6>; /* alt2 */
   };
};

What are you trying to achieve with gpio interrupts ?

Based on your needs you may not need gpio interruptions directly.

It also depends on how are you planning to handle interrupts:

• sysfs gpio export (/sys/class/gpio/)
• kernel module
• Other ?

After struggling with gpios and dts on the beagle bone black I recommend not to change the dts unless necessary as it may change often (kernel compatibility updates...) and require good knowledge of the board.