old interface ls /sys/class/gpio/
new interface ls /dev/gpiochip*


/sys/class/leds (must enable)

sudo apt update
sudo apt install gpiod -y

new interface
sudo gpiodetect
gpioinfo pinctrl-bcm2835 or ls /dev/gpiochip* and gpioinfo 0
sudo gpioset pinctrl-bcm2835 18=1 or gpioset 0 18=1

enable driver then modify device tree
device tree not necessary for usb (can describe itself at runtime)

Linux kernel menuconfig ---> Device drivers ---> LED Support ---> LED Class support and led support for led gpio connected and led trigger support ---> all


Kernel SRC/Documentation/devicetree/bindings/
Kernel SRC/Documentation/devicetree/bindings/leds/leds-gpio.yaml

copy example

Kernel SRC/arch/arm/boot/dts/nxp/imx/imx6dl-colibri-aster.dts
driver:
Kernel SRC/drivers/leds/leds-gpio.c

"compatible = "gpio-leds"

Kernel SRC/arch/arm/boot/dts/nxp/imx/imx6dl.dtsi
(base device tree)dtsi contains aliases to gpio eg &gpio1

eg

leds {
		compatible = "gpio-leds";
		led-0 {
			gpios = <&gpio0 18 GPIO_ACTIVE_HIGH>;
			function = LED_FUNCTION_STATUS;
			color = <LED_COLOR_ID_BLUE>;
			default-state = "off";
		};

	};

Make a copy of the dts (typically in board/<company>/<boardname>). Point to that dts in the "Out of tree custom DTS" menu entry (BR2_LINUX_KERNEL_CUSTOM_DTS_PATH) in the Buildroot menuconfig. Obviously, you need to build a kernel and enable the device tree option for this to work or just add out-of-tree device tree directory for folder containing custom dts.

ls -l /proc/device-tree/
ls -l /proc/device-tree/leds/

cd /sys/class/leds
ls
cd red:status
cat max_brightness
echo 0 > brightness (off)
echo 1 > brightness (on)
cat trigger
echo timer > trigger
echo delay_off etc


Now we need to create the overlay directory that will add additional configuration files to the target’s firmware image. Let’s create a directory called board/raspberrypi/rootfs_overlay/, and subdirectories for the actual files.

((PAD_ETH_TXP)/UART3_RX/IIC1_SCL/XGPIOB[25]/PWM[13]/CAM_MCLK0/SPI1_SDO/IIS2_LRCK)__[HIZ]|________PAD_ETH_TXP___EPHY_RXN
62
((PAD_ETH_TXM)/UART3_RTS/IIC1_SDA/XGPIOB[24]/PWM[12]/CAM_MCLK1/SPI1_SDI/IIS2_BCLK)__[HIZ]|________PAD_ETH_TXM___EPHY_RXP
63
((PAD_ETH_RXP)/UART3_TX/CAM_MCLK1/XGPIOB[27]/PWM[15]/CAM_HS0/SPI1_SCK/IIS2_DO)__[HIZ]|________PAD_ETH_RXP___EPHY_TXN
64
((PAD_ETH_RXM)/UART3_CTS/CAM_MCLK0/XGPIOB[26]/PWM[14]/CAM_VS0/SPI1_CS_X/IIS2_DI)__[HIZ]|________PAD_ETH_RXM___EPHY_TXP
65

XGPIO?