xref: /freebsd-11-stable/contrib/dtc/Documentation/dts-format.txt

Device Tree Source Format (version 1)
=====================================

The Device Tree Source (DTS) format is a textual representation of a
device tree in a form that can be processed by dtc into a binary
device tree in the form expected by the kernel.  The description below
is not a formal syntax definition of DTS, but describes the basic
constructs used to represent device trees.

Node and property definitions
-----------------------------

Device tree nodes are defined with a node name and unit address with
braces marking the start and end of the node definition.  They may be
preceded by a label.

	[label:] node-name[@unit-address] {
		[properties definitions]
		[child nodes]
	}

Nodes may contain property definitions and/or child node
definitions. If both are present, properties must come before child
nodes.

Property definitions are name value pairs in the form:
	[label:] property-name = value;
except for properties with empty (zero length) value which have the
form:
	[label:] property-name;

Property values may be defined as an array of 8, 16, 32, or 64-bit integer
elements, as NUL-terminated strings, as bytestrings or a combination of these.

* Arrays are represented by angle brackets surrounding a space separated list
  of C-style integers or character literals.  Array elements default to 32-bits
  in size.  An array of 32-bit elements is also known as a cell list or a list
  of cells.  A cell being an unsigned 32-bit integer.

	e.g. interrupts = <17 0xc>;

* A 64-bit value can be represented with two 32-bit elements.

	e.g. clock-frequency = <0x00000001 0x00000000>;

* The storage size of an element can be changed using the /bits/ prefix.  The
  /bits/ prefix allows for the creation of 8, 16, 32, and 64-bit elements.
  The resulting array will not be padded to a multiple of the default 32-bit
  element size.

	e.g. interrupts = /bits/ 8 <17 0xc>;
	e.g. clock-frequency = /bits/ 64 <0x0000000100000000>;

* A NUL-terminated string value is represented using double quotes
  (the property value is considered to include the terminating NUL
  character).

	e.g. compatible = "simple-bus";

* A bytestring is enclosed in square brackets [] with each byte
  represented by two hexadecimal digits.  Spaces between each byte are
  optional.

	e.g. local-mac-address = [00 00 12 34 56 78]; or equivalently
	     local-mac-address = [000012345678];

* Values may have several comma-separated components, which are
  concatenated together.
	e.g. compatible = "ns16550", "ns8250";
	     example = <0xf00f0000 19>, "a strange property format";

* In an array a reference to another node will be expanded to that node's
  phandle.  References may by '&' followed by a node's label:
	e.g. interrupt-parent = < &mpic >;
  or they may be '&' followed by a node's full path in braces:
	e.g. interrupt-parent = < &{/soc/interrupt-controller@40000} >;
  References are only permitted in arrays that have an element size of
  32-bits.

* Outside an array, a reference to another node will be expanded to that
  node's full path.
	e.g. ethernet0 = &EMAC0;

* Labels may also appear before or after any component of a property
  value, or between elements of an array, or between bytes of a bytestring.
	e.g. reg = reglabel: <0 sizelabel: 0x1000000>;
	e.g. prop = [ab cd ef byte4: 00 ff fe];
	e.g. str = start: "string value" end: ;


File layout
-----------

Version 1 DTS files have the overall layout:
	/dts-v1/;

	[memory reservations]

	/ {
		[property definitions]
		[child nodes]
	};

* The "/dts-v1/;" must be present to identify the file as a version 1
  DTS (dts files without this tag will be treated by dtc as being in
  the obsolete "version 0", which uses a different format for integers
  amongst other small but incompatible changes).

* Memory reservations define an entry for the device tree blob's
  memory reservation table.  They have the form:
	e.g. /memreserve/ <address> <length>;
  Where <address> and <length> are 64-bit C-style integers.

* The / { ... }; section defines the root node of the device tree.

* C style (/* ... */) and C++ style (// ...) comments are supported.



	-- David Gibson <david@gibson.dropbear.id.au>
	-- Yoder Stuart <stuart.yoder@freescale.com>
	-- Anton Staaf <robotboy@chromium.org>