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Device Tree (Devicetree)
Purpose
Guide agents through Linux device tree source (DTS): syntax, bindings, phandles, overlays, and how the kernel OF (Open Firmware) layer parses hardware description into platform_device instances.
When to Use
- Platform driver not probing — DT mismatch
- Adding a new board
.dtsor fragment overlay - Understanding
compatible,reg,interrupts,clocksproperties - Cross-checking hardware with
skills/kernel-dev/platform-device-model
Workflow
1. DTS structure
dts
/dts-v1/;
#include "soc.dtsi"
/ {
model = "My Board";
compatible = "vendor,my-board", "vendor,soc-family";
soc {
uart0: serial@40011000 {
compatible = "vendor,uart";
reg = <0x40011000 0x400>;
interrupts = <GIC_SPI 38 IRQ_TYPE_LEVEL_HIGH>;
clocks = <&clk_uart0>;
status = "okay";
};
};
};2. Key properties
| Property | Meaning |
|---|---|
compatible | Driver match string (most specific first) |
reg | MMIO address + length ( #address-cells, #size-cells ) |
interrupts | IRQ specifier (interrupt parent defines cells) |
clocks / clock-names | phandle to clock provider |
status | "disabled" skips probe |
3. Phandles
dts
clk_uart0: clock-uart {
compatible = "vendor,clk";
#clock-cells = <0>;
};
serial@... {
clocks = <&clk_uart0>; /* phandle reference */
};4. Kernel parsing
OF core reads DTB at boot
├── of_platform_populate() creates platform_devices
└── driver `.of_match_table` matches `compatible`c
static const struct of_device_id my_of_match[] = {
{ .compatible = "vendor,uart" },
{ }
};
MODULE_DEVICE_TABLE(of, my_of_match);5. Compile and inspect
bash
dtc -I dts -O dtb -o board.dtb board.dts
dtc -I fs -O dts /proc/device-tree 2>/dev/null | less
ls /sys/firmware/devicetree/base/Bindings live at devicetree.org — always cite binding name in commits.
6. Overlays (configfs)
bash
# Runtime overlay apply (when CONFIG_OF_OVERLAY)
mkdir -p /config/device-tree/overlays/my-overlay
cat my-overlay.dtbo > /config/device-tree/overlays/my-overlay/dtbo7. Agent usage
/device-tree Write DTS fragment for I2C sensor on i2c1 with interrupt on GPIO5Common Problems
| Symptom | Cause | Fix |
|---|---|---|
| Driver not bound | compatible typo | Match driver's of_match_table |
| Wrong MMIO | #address-cells mismatch | Follow SoC .dtsi |
| IRQ not firing | Wrong interrupt parent/cells | Copy from working board DTS |
| Probe defer loop | Clock/regulator missing | -EPROBE_DEFER supplier in DT |
| Overlay fails | Symbol unresolved | __fixups__ / label exports |
Related Skills
skills/kernel-dev/platform-device-model— probe and sysfsskills/kernel/device-drivers—devm_of_iomapskills/baremetal/datasheet-and-refmanual-reading— HW to DT mappingskills/embedded/zephyr— Zephyr devicetree (different tooling)skills/kernel-dev/bus-drivers-i2c-spi— bus node children
