Device Tree Reference

Top Device Tree page

Device Tree Usage
If Device Tree is new to you, start with Device Tree Usage page. That page describes what Device Tree source looks like. It walks through building the source for a new machine. It describes the basic concepts, shows specific examples, and covers some advanced features.

Device Tree Usage page was previously located at devicetree.org.

Presentations, Papers, and Articles
The Device Tree presentations, papers, and articles page is organized by topic area and by date.

Device Tree Mysteries
If you can not find a specific piece of information elsewhere, it might be on the Device_Tree_Mysteries page.

Linux Specific
Device Tree Linux

Standards
[[Media:Power_ePAPR_APPROVED_v1.1.pdf | Power.org Standard for Embedded Power Architecture Platform Requirements (ePAPR) v1.1]] Source: https://www.power.org/documentation/power-org-standard-for-embedded-power-architecture-platform-requirements-epapr-v1-1-2/

The ePAPR is currently being updated with a new name of Devicetree Specification Documentation.

Linux Man pages
Linux man pages are a work in progress.

The current version of the pages can be downloaded or built locally.

Kernel Source Documentation
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 (in alphabetic order) are:


 * ABI/testing/sysfs-firmware-ofw
 * description of /sys/firmware/devicetree/* on the target system


 * devicetree/bindings
 * 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


 * devicetree/bindings/ABI.txt
 * comments on stable binding and general bindings rules


 * devicetree/bindings/property-units.txt
 * how to name properties which have a unit of measure


 * devicetree/bindings/resource-names
 * *-name properties containing an ordered list of names corresponding to another property


 * devicetree/bindings/submitting-patches.txt
 * important details for patch submitters and kernel maintainers


 * devicetree/bindings/vendor-prefixes.txt
 * vendor prefix registry


 * devicetree/booting-without-of.txt
 * original powerpc document on booting without Open Firmware


 * devicetree/changesets.txt
 * Description of changesets. Apply changes such that full set of changes is applied successfully or none are.


 * devicetree/dynamic-resolution-notes.txt
 * Implementation of resolver, used when applying overlays.


 * devicetree/of_unittest.txt
 * How data for device tree unit tests is added to the kernel


 * devicetree/overlay-notes.txt
 * How data for device tree unit tests is added to the kernel


 * devicetree/usage-model.txt
 * Implementation of overlay

Some subsystems have overview bindings descriptions under devicetree/bindings/:


 * bus/mvebu.bus
 * bus/simple-pm-bus.txt
 * clock/clock-bindings.txt
 * display/mipi-dsi-bus.txt
 * dma/dma.txt
 * gpio/gpio.txt
 * hwlock/hwlock.txt
 * iio/iio.txt
 * interrupt-controller/interrupts.txt
 * iommu/iommu.txt
 * lpddr2/lpddr2.txt
 * mailbox/mailbox.txt
 * memory-controllers/mvebu-devbus.txt
 * mfd/mfd.txt
 * mips/cavium/bootbus.txt
 * mmc/mmc.txt


 * pci/pci.txt
 * phy/phy-bindings.txt
 * pinctrl/pinctrl-bindings.txt
 * power_supply/power_supply.txt
 * pwm/pwm.txt
 * regmap/regmap.txt
 * regulator/regulator.txt
 * reserved-memory/reserved-memory.txt
 * reset/reset.txt
 * spi/spi-bus.txt
 * spmi/spmi.txt
 * thermal/thermal.txt
 * xillybus/xillybus.txt

Device Tree Source

 * [[Media:Power_ePAPR_APPROVED_v1.1.pdf | 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


 * presentations
 * "Device Tree for Dummies", ELC 2014 by Thomas Petazzoni
 * [[Media:petazzoni-device-tree-dummies_0.pdf | PDF]]
 * YouTube video

Bindings
Bindings are documented in
 * Standards documents
 * Linux kernel source tree

Subsystem specific

 * gpio / pinctrl


 * interrupts


 * timers


 * etc

Compiling source into .dtb (FDT binary blob)

 * via kernel make system
 * all configured .dtb
 * make dtbs
 * specific .dtb
 * make arch/arm/boot/dts/qcom-apq8074-dragonboard.dtb


 * via generated script in build directory
 * arch/arm/boot/dts/.*.dtb.cmd
 * arch/${ARCH}/boot/dts/.*.dtb.cmd


 * Documentation/manual.txt Device Tree Compiler Manual

FDT format
Other names for Flattened Device Tree (FDT) are "binary blob" and ".dtb".

The format of version 17 of the FDT is described in chapter 8, "Flat Device Tree Physical Structure" of the [[Media:Power_ePAPR_APPROVED_v1.1.pdf | ePAPR v1.1]].

Section "II - The DT block format" of booting-without-of.txt is a more expansive description of the format of FDT.

Install

 * make dtbs_install
 * installs in /boot/dtbs/


 * many other ways to install ....

Debugging

 * tutorials
 * "Solving Device Tree Issues" (updated), ELCE October 2015 by Frank Rowand
 * [[Media:Dt_debugging_elce_2015_151006_0421.pdf | PDF slides]]
 * Supporting Resources (patches, etc)


 * diffing .dts, .dtb, /proc/devicetree/
 * scripts/dtc/dtx_diff
 * in the Linux kernel source tree as of 4.6-rc1
 * use cases, advantages, and things to be aware of are described in [[Media:Dt_debugging_elce_2015_151006_0421.pdf | "Solving Device Tree Issues"]] (updated), ELCE October 2015 by Frank Rowand (PDF). dtx_diff is referred to as "dtdiff" in this presentation.


 * 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

Linux kernel source tree

 * dtc (Device Tree Compiler) - 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 located in scripts/dtc/ in the kernel source directory. New versions are periodically pulled from the upstream project.
 * The upstream project is maintained in
 * https://git.kernel.org/cgit/utils/dtc/dtc.git
 * git clone git://git.kernel.org/pub/scm/utils/dtc/dtc.git
 * Documentation
 * Documentation/manual.txt Device Tree Compiler Manual
 * Documentation/dts-format.txt Device Tree Source Format
 * The Maintainers are listed in the file README


 * dtx_diff - 1) compares two dtX files, 2) compiles a single dtX file (using the normal Linux includes and .config) then decompiles that into a device tree source file. A dtX file can be a device tree source file, a device tree compiled file (aka .dtb, FDT, or device tree blob), or a file system based subtree (either /proc/device-tree on the target system, or /proc/device-tree can be tarred on the target system and untarred on the system containing dtx_diff).

external
"The device tree generator is a Xilinx EDK tool that plugs into the Automatic BSP Generation features of the tool, XPS"
 * Xilinx EDK device-tree generator - Generates an FDT from Xilinx FPGA design files.
 * http://xilinx.wikidot.com/device-tree-generator

other projects using Device Tree
FreeBSD FlattenedDeviceTree wiki

FreeBSDArmBoards wiki

Glossary

 * .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.