1. Linux Device Driver Model
2. The Core Data Structure Of Linux Device Driver Model Is
3. Linux Io Model
4. Linux Kernel Device Driver Model
5. Linux Device Driver Pdf

• 7Device Tree Related Communications
• 17Overlays
• 19Compiling source into .dtb (FDT binary blob)
  • 19.1via Linux kernel make system
• 26Tools in Linux kernel source tree
• 27Tools external to Linux kernel source tree
• 28Testing
• 29Other projects using Device Tree
• 30Glossary

Introduction

PCI device hierarchy is represented internally. Though the PCI tree is physically connected to other devices, this hierarchy is autonomous with regard to other internal device representa-tions. 2 The Linux Device Model Core In order to construct a global device tree, a common device structure was created to rep-resent each physical device in. Linux Kernel Documentation. Documentation / driver-model / driver.txt. Custom Search Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 EST. 1 2 Device Drivers 3 4 See the kerneldoc for the struct devicedriver. These fields are assumed to be valid at all times and may be 94 used by the device model core or the bus driver. In the 2.5 Linux kernel development series, a unified device driver model framework was created by Pat Mochel. This framework consists of a number of common structures and functions all device driver subsystems have been converted to use.

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 thesource 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.

What Is Device Tree

The primary purpose of Device Tree in Linux is to provide a way to describe non-discoverable hardware. This information was previously hard coded in source code.

Some more background on what Device Tree is, advantages, and competing solutions, see this page.Most of the contents of this page was previously located at Device_Tree, which nowredirects to Device_Tree_Reference.

Request for Documentation Suggestions

If you have any comments or suggestions about the Device Tree documentation on elinux.org, please send themto frowand (dot) list (at) gmail (dot) com

I am currently trying to make the information more organized, more comprehensive, and a morecomplete index of information available elsewhere. I am looking for comments on what isincorrect, incomplete, or missing. I would appreciate pointers to good documentation,tutorials, etc that I can link to.

History

Future

• How device tree is changing and where it is headed
  • Includes Linux Plumbers conference, Kernel Summit, etc

Device Tree Related Communications

Device-Tree irc

The Device Tree irc channel is #devicetree on freenode.net.

You are likely to find many people connected to the channel, but manyof them are not actively monitoring traffic. There may be a delay ofseveral days or weeks before a question or comment is acknowledged.

Device-tree Mailing List

This list contained all devicetree related discussion until February 2014.At that time, the devicetree.spec and devicetree.compiler lists werecreated to provide lower volume lists for those specific topic areas.

After July 2013:

Up through July 2013:

Core devicetree binding / Devicetree Specification Mailing List

Created February 2014.

The devicetree.spec list is for 'core' binding discussions; anything thataffects entire subsystems or the kinds of things that would make senseto be added to the ePAPR Devicetree Specification.

Individual device bindings continue to be posted todevicetree@vger.kernel.org, but anything affecting subsystems orgeneric patterns should be posted to this list.

After April 28, 2016:

The creation and updating of the Devicetree Specificationis also discussed on this list.

Device-tree Compiler and Tools Mailing List

Created February 2014.

The devicetree.compiler list is for discussion related to dtc and other tools.

It is specifically for discussing dt tooling topics(parsing, schema validation, data format, etc).

Presentations, Papers, and Articles

The Device Tree presentations, papers, and articlespage 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

Standards

Devicetree Specification Release 0.2, located on thedevicetree.org web sitehas superseded the ePAPR for the Linux kernel. The specification is meant to be OS independent.The Linux kernel devicetree maintainers are actively involved in the specification process.

The Devicetree Specification will continue to be updated.

Open Power Foundation Linux on Power Architecture Platform Reference (LoPAPR), v1.1, 24 march 2016
Source: https://members.openpowerfoundation.org/document/dl/469

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/

Device Tree Source Format

• Devicetree Specification Release 0.2
  • chapter 2 'The Devicetree'
  • chapter 6 'Devicetree Source Format (version 1)'

• Power.org Standard for Embedded Power Architecture Platform Requirements (ePAPR) v1.1
  • superseded by the Devicetree Specification
  • 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

• presentations
  • 'Device Tree for Dummies', ELC 2014 by Thomas Petazzoni

• Undocumented
  • Device_Tree_Source_Undocumented contains some information not documented elsewhere

Bindings

Bindings are documented in

Bindings Documentation in Linux Kernel Source Tree

Documentation files about device tree is available in the Linux kernel source atDocumentation/devicetree

Specific bindings specifications are located in the Linux kernel source at:Documentation/devicetree/bindings

Before submitting a binding patch, read these:

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

• devicetree/bindings/writing-bindings.txt
  • DOs and DON'Ts for designing and writing Devicetree bindings

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

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/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/vendor-prefixes.txt
  • vendor prefix registry

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

Other Documentation in Linux Kernel Source Tree

• 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
  • Kernel internal implementation notes on overlays

• devicetree/usage-model.txt
  • Overview of: Linux and the Device Tree

Subsystem specific

• gpio / pinctrl

• interrupts

• timers

• etc

Overlays

Mainline Linux Support

Run time overlay apply and run time overlay remove from user spaceare not supported in the mainline kernel. There are out of treepatches to implement this feature via an overlay manager. Theoverlay manager is used successfully by many users for specificoverlays on specific boards with specific environments and use cases.However, there are many issues with the Linux kernel overlayimplementation due to incomplete and incorrect code. The overlaymanager has not been accepted in mainline due to these issues. Oncethese issues are resolved, it is expected that some method of run timeoverlay apply and overlay removal from user space will be supported bythe Linux kernel.

There is a possibility that overlay apply and overlay remove supportcould be phased in slowly, feature by feature, as specific issues areresolved.

Boot Loader Support

An alternative to Linux kernel run time overlay apply is boot loaderoverlay apply. For example, U-Boot supports overlay apply. Thismethod of overlay apply avoids the complications and issues ofrun time Linux kernel overlay apply. This method is likely tobe more robust and less problematic than run time Linux kerneloverlay apply and is thus the recommended technique.

Overlay Source Format

In early overlay days, much of the overlay metadata was hand coded inthe overlay source file. The current dtc compiler in the Linux kernelsource tree eliminates the need for this hand coding. It is expectedthat the Linux kernel overlay apply code will at some time in the futurerefuse to apply an overlay compiled from source with hand coded metadata.The metadata includes fragment nodes and nodes with names beginningwith an underscore, such as __overlay__, __fixup__, __local_fixup__,and __symbols__.

For examples of transforming overlay source from the hand codedmetadata form, see slides 29 - 34 of the ELCE 2018 Devicetree BoF [PDF].

Device Tree Source Validation

See device tree future validation work.

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The most basic validation is warnings from the dtc compiler. Noisy checksare disabled by default. Enable the noisy checks by specifying 'W=1' onthe make command line.

Compiling source into .dtb (FDT binary blob)

Documentation/manual.txt Device Tree Compiler Manual

via Linux kernel make system

All configured .dtb

A specific .dtb

This is an example of compiling arch/arm/boot/dts/qcom-msm8960-cdp.dts

The make target is the name of the .dts file, with '.dts' changed to '.dtb'.

Check that the config option that enables the dtb is set, for example:

Either specify the correct architecture in the make command (or export the ARCH)

via generated script in build directory

After a .dtb has been built by the Linux kernel make system, files containing the precise buildcommands will remain in the build directory:

• arch/arm/boot/dts/.*.dtb.cmd
• arch/${ARCH}/boot/dts/.*.dtb.cmd

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 5, 'Flat Devicetree Physical Structure'of the Devicetree Specification Release 0.2.

The format of version 17 of the FDT is described in chapter 8, 'Flat Device Tree Physical Structure'of the ePAPR v1.1 (superseded by the Devicetree Specification).

Section 'II - The DT block format' ofbooting-without-of.txtis a more expansive description of the format of FDT.

Install

• make dtbs_install
  • installs in /boot/dtbs/<kernel version>

• many other ways to install ..

Boot loaders

Booting

Debugging

(Also see Device_Tree_presentations_papers_articles#debug.)

• tutorials
  • 'Solving Device Tree Issues' (updated), ELCE October 2015 by Frank Rowand

• 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 'Solving Device Tree Issues' (updated), ELCE October 2015 by Frank Rowand (PDF). dtx_diff is referred to as 'dtdiff' in this presentation.

• locating source file and line for nodes and properties
  • scripts/dtc/dtx_diff --annotate
    • in the Linux kernel source tree as of 5.0-rc1
    • useful for 'dtx_diff DTx'
    • not useful for 'dtx_diff DTx_1 DTx_2'

• 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'

For newer kernels where the CONFIG_PROC_DEVICETREE option does not exist, /proc/device-tree will becreated 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 statementsto 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:

Tools in Linux kernel source tree

dtc (in kernel)

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.
  • dtc is built by the Linux kernel build process as a dependency when needed. If you want to explicitly build it in the Linux kernel source tree, use the command: make scripts
• Information about the upstream project is in a nearby section.
  • 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

dtx_diff has two modes of operation:

• compare two dtX files
• compile 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).

Examples of how to use dtx_diff can be found in 'Solving Device Tree Issues' (updated), ELCE October 2015, Frank Rowand . Note that dtx_diff was named 'dtdiff' in the presentation.

dtx_diff was merged in 4.6-rc1

--annotate was merged in 5.0-rc1

dt_to_config

dt_to_config is a tool to provide information about the Linux kernel configuration options needed by a given device tree.

dt_to_config can also report on whether the kernel configuration options are set correctly.

Examples of how to use dt_to_config and some limitations to be aware of can be found in 'Solving Device Tree Issues - part 2', LinuxCon Japan, July 2016, Frank Rowand .

dt_to_config was merged in 4.8-rc1.

Tools external to Linux kernel source tree

dtc (upstream project)

The dtc (Device Tree Compiler) upstream project is periodically pulled into the Linux kernel source tree.The upstream project is maintained in

• git clone git://git.kernel.org/pub/scm/utils/dtc/dtc.git

Info on submitting patches is in section 1.1 of Documentation/manual.txt

Building dtc, fdtdump, and other tools in the upstream project:

• make

dts-mode

From the github README.mkd: a quick attempt at getting basic highlighting for Device Tree syntax in emacs.

From the announcement: Today I cobbled together a rudimentary devicetree major mode foremacs. At this point it's pretty much limited to rather basic syntaxhighlighting but works fairly well all things considered. It can befound on Github[1]. Patches are of course quite welcome.

Project location on [github].

I am not an emacs user, so I would appreciate any feedback on how useful this tool is and additionalinformation that could be added to this description (or if the tool is useless and should beremoved from this page). Email me at frowand (dot) list (at) gmail (dot) com

EDK

Linux Device Driver Model

• Xilinx EDK device-tree generator - Generates an FDT from Xilinx FPGA design files.

fdtdump

fdtdump is a tool to convert an FDT (flattened device tree, aka device tree blob) to source.

The dtc compiler is an alternate tool that also has an option to convert an FDT to source(-O dts).

fdtdump differs in some ways from 'dtc -O dts':

• fdtdump prints the FDT header as a source comment.
• The format of data differs in appearance (number of hex digits printed) but both formats result in the same FDT when compiled.
• The --scan option of fdtdump will search through a file that embeds an FDT, attempting to find the FDT. The embedded FDT will be converted to dts.

An unmaintained version of the source of fdtdump exists in the Linux kernel source tree.There is no makefile entry to build fdtdump in the Linux kernel source tree. fdtdumpmay be removed from the Linux kernel source tree in the future.

fdtdump is located in the dtc project andcan easily be built there.

Testing

linux kernel framework

Enable unit tests through config option CONFIG_OF_UNITTEST

• Device Drivers ---> Device Tree and Open Firmware support ---> Device Tree runtime unit tests

The unit tests will be performed near the end of the boot sequence. The start of the testsis indicated by:

An example test result summary is:

The unit tests are located in

• drivers/of/unittest.c
• drivers/of/unittest-data/

dtc

The Core Data Structure Of Linux Device Driver Model Is

The dtc tests are located in the upstream dtc project (see dtc (upstream project)).

Each test will report PASS or FAIL.

An example test result summary is:

Other projects using Device Tree

barebox

Linux Io Model

barebox bootloader

User manual: Devicetree support

BSD

BSD operating system

U-Boot

U-Boot bootloader

Zephyr

Linux Kernel Device Driver Model

Zephyr RTOS

Linux Device Driver Pdf

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