gpio-demo.dts (modern dtc)

/dts-v1/;
/plugin/;

#include <dt-bindings/board/am335x-bbw-bbb-base.h>
#include <dt-bindings/pinctrl/am33xx.h>
#include <dt-bindings/gpio/gpio.h>

// file identification
&{/chosen} {
    overlays {
        // XXX change property name to the name of this overlay (excluding .dts file suffix)
        gpio-demo = __TIMESTAMP__;
    };
};

// XXX caution: not compatible with cape-universal!

// A udev rule along these lines is recommended to create symlinks in /dev/gpio/
//
//  SUBSYSTEM=="subsystem", KERNEL=="gpio", ACTION=="add", \
//      RUN+="/bin/mkdir -p /dev/gpio"
//
//  SUBSYSTEM=="gpio", ACTION=="add", TEST=="value", ATTR{label}!="sysfs", \
//      RUN+="/bin/ln -sT '/sys/class/gpio/%k' /dev/gpio/%s{label}"

&{/} {
    // If you want to use multiple overlays that do gpio configuration, be
    // sure that each uses a different device tree node!
    gpio-demo {
        compatible = "gpio-of-helper";

        // It is usually not *strictly* required to perform pinmux for
        // GPIOs since this is typically their default, but it's good
        // practice to do it anyway since:
        // 1. it makes *sure* the pinmux is right
        // 2. you can configure internal pull-up/down
        // 3. it lets the kernel know the pins are in use
        pinctrl-names = "default";
        pinctrl-0 = <&gpio_demo_pins>;

        // Note that gpio numbers for each pin can be found in the
        // comments in include/bone/black.h

        // input only, active-low; connect button between pin and gnd.
        // declaring the gpio as ACTIVE_LOW means the value reads as 1
        // when the button is pressed.
        button {
            gpio = <&gpio2 2 GPIO_ACTIVE_LOW>;  // P8.07
            input;
        };

        // output only, active-low, initially high (inactive)
        reset-thing {
            gpio = <&gpio2 3 GPIO_ACTIVE_LOW>;  // P8.08
            init-high;
        };

        // note: GPIO_ACTIVE_LOW inverts the meaning of the value, but it
        // does not invert the meaning of "init-low" / "init-high" !


        // bidirectional, initially input
        input-bidi {
            gpio = <&gpio2 5 GPIO_ACTIVE_HIGH>;  // P8.09
            input;
            dir-changeable;
        };

        // bidirectional, initially output, initially low (inactive)
        output-bidi {
            gpio = <&gpio2 4 GPIO_ACTIVE_HIGH>;  // P8.10
            init-low;
            dir-changeable;
        };
    };
};

&am33xx_pinmux {
    gpio_demo_pins: gpio-demo {
        pinctrl-single,pins = <
            BONE_P8_07 (PIN_INPUT_PULLUP | MUX_MODE7 )  // gpio 2.02 / button
            BONE_P8_08 (PIN_INPUT_PULLUP | MUX_MODE7 )  // gpio 2.03 / reset-thing
            BONE_P8_09 (PIN_INPUT_PULLUP | MUX_MODE7 )  // gpio 2.05 / input-bidi
            BONE_P8_10 (PIN_INPUT_PULLUP | MUX_MODE7 )  // gpio 2.04 / output-bidi
        >;
    };
};