Device Tree Reference

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Top Device Tree page

Reference Manual

Introduction

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.

Miscellaneous Tips

Linux Drivers Device Tree Guide

Standards

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/

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

Some especially useful files are:

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

Device Tree Source

  • presentations

Bindings

Bindings are documented in

Subsystem specific

  • gpio / pinctrl
  • interrupts
  • timers
  • etc

Overlays

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

Install

  • make dtbs_install
    • installs in /boot/dtbs/<kernel version> ???? -- is this useful ???
  • many other ways to install ....

Boot loaders

Booting

Debugging

  • 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

Tools

"The device tree generator is a Xilinx EDK tool that plugs into the
Automatic BSP Generation features of the tool, XPS"

Man pages

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.

Definitions