Add LED to TK1 device tree

Robotics & Edge Computing Jetson & Embedded Systems Jetson TK1
1

We have a custom board with GPIO_X1_AUD_PX1 connected to an LED. I want to set up the device tree such that this LED is a heartbeat. I’ve added the following to the device tree, but don’t see any new entries under /sys/class/leds (the only thing there is mmc0::). I’ve made sure that CONFIG_LEDS_GPIO is configured, so it seems like there should be something there, even if it doesn’t work:

leds {
    compatible = "gpio-leds";
    heartbeat {
        label = "heartbeat";
        gpios = <&gpio TEGRA_GPIO(X, 1) 0>;
        linux,default-trigger = "heartbeat";
    };
};

I’ve observed that by adding TEGRA_GPIO(X, 1) to gpio-output-low (shown below) I can get the LED to turn on, which tells me that I’m referencing the right pin, at least.

gpio: gpio@6000d000 {
    gpio-init-names = "default";
    gpio-init-0 = <&gpio_default>;

    gpio_default: default {
        gpio-input = <
            ...
            >;
        gpio-output-low = <
            ...
            TEGRA_GPIO(X, 1)
            >;
        gpio-output-high = <
            ...
            >;
    };
};

For the sake of completeness, here is where it is in the pinmux of the device tree:

pinmux: pinmux {
    status = "okay";
    pinctrl-names = "default", "drive", "unused";
    pinctrl-0 = <&pinmux_default>;
    pinctrl-1 = <>;
    pinctrl-2 = <&pinmux_unused>;

    pinmux_default: common {
        ...
        gpio_x1_aud_px1 {
            nvidia,pins = "gpio_x1_aud_px1";
            nvidia,function = "safe";
            nvidia,pull = <TEGRA_PIN_PULL_DOWN>;
            nvidia,tristate = <TEGRA_PIN_DISABLE>;
            nvidia,enable-input = <TEGRA_PIN_DISABLE>;
        };
    };

    pinmux_unused: unused {
        ...
    };
};

I’ve looked at all the documentation in the kernel related to GPIOs and LEDs and several forum posts about related issues, but haven’t found anything. Any advice would be appreciated!

2

Figured it out… We had LEDS_GPIO enabled in the defconfig, but also needed to enable triggers.