GPIO configuartion in Device Tree Overlay and how to set a default value for an output pin


I´m currently getting more and more into the Device Tree and I have a basic overview how it works and how DTOs are written. I wrote an overlay to enable a GPIO as output. The Pinmux fragment works but I am not sure what is the “bone-pinmux-helper” (here in fragment@1) for. Some overlays I reviewed have this fragment and some not. So I´m not sure what it is doing and if I need this.

I created an little overlay here with this device tree overlay generator ( and commented my thoughts and question in blue.


compatible = “ti,beaglebone”, “ti,beaglebone-black”;
part_number = “BS_PINMODE_P8_26_0xf”;

exclusive-use =

fragment@0 {
target = <&am33xx_pinmux>;
overlay {
bs_pinmode_P8_26_0xf: pinmux_bs_pinmode_P8_26_0xf {
pinctrl-single,pins = <0x07c 0xf>;

fragment@1 {
target = <&ocp>; //targets the on-chip-peripherials (ocp) node in the Device Tree
overlay {
bs_pinmode_P8_26_0xf_pinmux { //creates a subnode with the name “bs_pinmode_P8_26_0xf_pinmux”

compatible = “bone-pinmux-helper”; //what is the “bone-pinmux-helper” and where can i find more documentation on that?

status = “okay”; //what is actiaved here?
pinctrl-names = “default”;
pinctrl-0 = <&bs_pinmode_P8_26_0xf>; //refering to pincontroll settings from bs_pinmode_P8_26_0xf in fragment@0

I want to drive an Enable Input of a display with that GPIO (don´t confuse with DE-Mode) which is active high. So my idea is that the display will be enabled when the DTO will be loaded through the cape manager. Is there a way to set 1 as a default value in the overlay for that output pin? (DTO is loaded > value is instantly 1?)


Well I did a little workaround and made a script that will init the GPIO via sysfs in the way I want at system start. But I don´t need to set the pinmux via the overlay for that as far as i know.

echo “61” > /sys/class/gpio/export #set gpio61 P8_26
echo “out” > /sys/class/gpio/gpio61/direction #set gpio61 as output
echo “1” > /sys/class/gpio/gpio61/value #set gpio61 to high

The fragment@1 I mentioned seems to affect


But I still dont understand what it actually does.