Device Tree

What is Device Tree?

Device tree is a data structure and language for describing hardware. To avoid reconfiguring the Linux kernel for each platform the concept of device tree was introduced. The kernel expects detailed information about the hardware that it runs on from the bootloader, such as U-Boot, reads the device information and configures devices and drivers appropriately.

Internally device tree is a tree of named nodes and properties. Nodes contain properties and child nodes, while properties are name–value pairs.

Here is a overlay used in Neutis to enable UART1. Based on this simple example we will describe a couple of sections.


/ {
        compatible = "allwinner,sun50i-h5";

        fragment@0 {
                target-path = "/aliases";
                __overlay__ {
                        serial1 = "/soc/serial@01c28400";

        fragment@1 {
                target = <&uart1>;
                 __overlay__ {
                        pinctrl-names = "default";
                        pinctrl-0 = <&uart1_pins>, <&uart1_rts_cts_pins>;
                        status = "okay";

The compatible property should be present in every node that represents a device. compatible is the key an operating system uses to decide which device driver to bind to a device.

The device tree fragments describe which target to overlay. In the first line we're setting which target for this fragment will be overlayed. The __overlay__ node itself contains the properties which will be used.

The last fragment enables the UART device by setting status property and specifies pin configuration nodes for pinctrl-0. The target for the overlay is UART1.

For more information on device tree please visit oficial specification.