gpio-demo.dts (raw overlay format)

/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
    fragment@0 {
        target-path = "/chosen";
        __overlay__ {
            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}"

    fragment@1 {
        target-path = "/";
        __overlay__ {
            // 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;
                };
            };
        };
    };

    fragment@2 {
        target = <&am33xx_pinmux>;
        __overlay__ {
            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
                >;
            };
        };
    };
};