Device tree: telling the kernel how the board is put together

A file that records which devices are attached at which addresses and pins. The reason the same kernel can run on many boards.

Why it is needed

The same kernel runs on several boards with only the device tree changed.

MCU firmware wrote pin numbers into the code for each board. Linux, to use the same kernel binary on many boards, separates the board configuration into a data file. That is the device tree (.dts → compile → .dtb).

Example: adding a temperature sensor on I2C

&i2c1 {
    status = "okay";
    clock-frequency = <400000>;
    tmp102@48 {
        compatible = "ti,tmp102";
        reg = <0x48>;
    };
};

compatible: the kernel finds the driver that matches this string and binds it
reg: the address (I2C address, memory-mapped address)
status = "okay": turns on a controller that is off by default

RoadmapSee where this note sits in Embedded Linux→

Overlays

Boards such as the Raspberry Pi add expansion-board configuration by laying an overlay (.dtbo) over the base .dtb. A dtoverlay= line in config.txt is exactly that.

Checking

After boot, check the tree that was actually applied under /proc/device-tree/
Check that the driver bound with dmesg | grep tmp102
If the pin-function selection (pinctrl) is missing, the controller is on but no signal reaches the pins