Device Tree Reference
- 1 Reference Manual
- 1.1 Introduction
- 1.2 Device Tree Usage
- 1.3 Linux Specific
- 1.4 Standards
- 1.5 Man pages
- 1.6 Kernel Source Documentation
- 1.7 Device Tree Source
- 1.8 Bindings
- 1.9 Subsystem specific
- 1.10 Overlays
- 1.11 Device Tree Source Validation
- 1.12 Compiling .dtb (FDT binary blob)
- 1.13 Install
- 1.14 Boot loaders
- 1.15 Booting
- 1.16 Debugging
- 1.17 Debugging - random hints
- 1.18 Tools
- 1.19 Glossary
- 1.20 Definitions
Device Tree Usage
The Device Tree Usage page was previously located at devicetree.org
It walks through how to write a device tree for a new machine.
It is intended to provide an overview of device tree concepts and how they are used to describe a machine.
Power.org Standard for Embedded Power Architecture Platform Requirements (ePAPR) v1.1
The ePAPR is currently being updated with a new name of Devicetree Specification Documentation.
man pages are a work in progress.
The current version of the pages can be downloaded or built locally.
Kernel Source Documentation
The device tree core source files under drivers/of/ contain DocBook format comments, but there is not yet a DocBook document that includes them.
Documentation files about device tree is available in the Linux kernel source at Documentation/devicetree
Specific bindings specifications are located in the Linux kernel source at: Documentation/devicetree/bindings
Some especially useful files are:
- description of /sys/firmware/devicetree/* on the target system
- the bindings directory has details about the syntax and expected elements for each device type representable in the dts and used by kernel frameworks and drivers
- comments on stable binding and general bindings rules
- not yet mainline: devicetree/bindings/property-units.txt
- how to name properties which have a unit of measure
- *-name properties containing an ordered list of names corresponding to another property
- important details for patch submitters and kernel maintainers
- vendor prefix registry
- original powerpc document on booting without Open Firmware
- information about different elements of bindings
Some subsystems have overview bindings descriptions under devicetree/bindings/:
Device Tree Source
- Power.org Standard for Embedded Power Architecture Platform Requirements (ePAPR) v1.1
- chapter 2 "The Device Tree"
- Appendix A "Device Tree Source Format (Version 1)"
- dtc compiler repository documentation
- Documentation/dts-format.txt Device Tree Source Format
- differences between ePAPR and the Linux dtc compiler
Bindings are documented in
- gpio / pinctrl
Device Tree Source Validation
Compiling .dtb (FDT binary blob)
- via kernel make system
- all configured .dtb
- make dtbs
- specific .dtb
- make arch/arm/boot/dts/qcom-apq8074-dragonboard.dtb
- all configured .dtb
- via generated script in build directory
- Documentation/manual.txt Device Tree Compiler Manual
- make dtbs_install
- installs in /boot/dtbs/<kernel version>
- many other ways to install ....
- diffing .dts, .dtb, /proc/devicetree/
- locating source location for properties
- boot time messages
- device creation
- driver registration
- binding driver to device
- deferred binding
Debugging - random hints
You can set CONFIG_PROC_DEVICETREE to be able to see the device tree information in /proc after booting. Build the kernel with this option set to 'Y', boot the kernel, then 'cd /proc/device-tree'
/proc/device-tree still does not exist. Now what??? Is CONFIG_PROC_FS enabled? Is CONFIG_OF enabled? Does /sys/firmware/devicetree/base exist? (Note that this path is not an ABI, but currently /proc/devicetree is a soft link to this location.) Did the bootloader load a devicetree? (Check the boot console or use dmesg to print the boot messages.)
For newer kernels where the CONFIG_PROC_DEVICETREE option does not exist, /proc/device-tree will be created if CONFIG_PROC_FS is set to 'Y'.
You might also try CONFIG_DEBUG_DRIVER=Y.
Also, often, you can set the line: "#define DEBUG 1" to an individual C file, to produce add debug statements to the routines in that file. This will activate any pr_debug() lines in the source for that file.
Alternatively, you can add the following to drivers/of/Makefile:
CFLAGS_base.o := -DDEBUG CFLAGS_device.o := -DDEBUG CFLAGS_platform.o := -DDEBUG CFLAGS_fdt.o := -DDEBUG
- Device Tree Compiler (dtc) - converts between the human editable device tree source "dts" format and the compact device tree blob "dtb" representation usable by the kernel or assembler source. dtc is also a dtb decompiler.
- The linux version of dtc is maintained in scripts/dtc/ in the kernel source directory.
- The upstream project is maintained in
- The Maintainers are listed in the file README
- Xilinx EDK device-tree generator - Generates an FDT from Xilinx FPGA design files.
"The device tree generator is a Xilinx EDK tool that plugs into the Automatic BSP Generation features of the tool, XPS"
- .dtb - File name suffix, by convention, for compiled devicetree.
- .dts - File name suffix, by convention, for devicetree source.
- .dtsi - File name suffix, by convention, for devicetree source to be included by a .dts or .dtsi file.
- Binary Blob - File containing a compiled devicetree.
- dtc - Devicetree compiler.
- EDT Expanded Device Tree - A copy of an FDT, but converted to kernel data structures, in the kernel memory space.
- FDT Flattened Device Tree - A copy of a binary blob in the kernel memory space.