symbian-qemu-0.9.1-12/dtc-trunk/Documentation/dts-format.txt
author martin.trojer@nokia.com
Fri, 31 Jul 2009 15:01:17 +0100
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Device Tree Source Format (version 1)
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=====================================
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The Device Tree Source (DTS) format is a textual representation of a
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device tree in a form that can be processed by dtc into a binary
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device tree in the form expected by the kernel.  The description below
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is not a formal syntax definition of DTS, but describes the basic
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constructs used to represent device trees.
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Node and property definitions
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-----------------------------
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Device tree nodes are defined with a node name and unit address with
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braces marking the start and end of the node definition.  They may be
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preceded by a label.
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	[label:] node-name[@unit-address] {
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		[properties definitions]
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		[child nodes]
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	}
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Nodes may contain property definitions and/or child node
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definitions. If both are present, properties must come before child
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nodes.
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Property definitions are name value pairs in the form:
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	[label:] property-name = value;
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except for properties with empty (zero length) value which have the
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form:
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	[label:] property-name;
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Property values may be defined as an array of 32-bit integer cells, as
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NUL-terminated strings, as bytestrings or a combination of these.
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* Arrays of cells are represented by angle brackets surrounding a
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  space separated list of C-style integers
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	e.g. interrupts = <17 0xc>;
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* A 64-bit value is represented with two 32-bit cells.
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	e.g. clock-frequency = <0x00000001 0x00000000>;
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* A NUL-terminated string value is represented using double quotes
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  (the property value is considered to include the terminating NUL
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  character).
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	e.g. compatible = "simple-bus";
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* A bytestring is enclosed in square brackets [] with each byte
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  represented by two hexadecimal digits.  Spaces between each byte are
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  optional.
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	e.g. local-mac-address = [00 00 12 34 56 78]; or equivalently
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	     local-mac-address = [000012345678];
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* Values may have several comma-separated components, which are
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  concatenated together.
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	e.g. compatible = "ns16550", "ns8250";
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	     example = <0xf00f0000 19>, "a strange property format";
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* In a cell array a reference to another node will be expanded to that
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  node's phandle.  References may by '&' followed by a node's label:
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	e.g. interrupt-parent = < &mpic >;
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  or they may be '&' followed by a node's full path in braces:
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	e.g. interrupt-parent = < &{/soc/interrupt-controller@40000} >;
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* Outside a cell array, a reference to another node will be expanded
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  to that node's full path.
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	e.g. ethernet0 = &EMAC0;
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* Labels may also appear before or after any component of a property
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  value, or between cells of a cell array, or between bytes of a
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  bytestring.
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	e.g. reg = reglabel: <0 sizelabel: 0x1000000>;
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	e.g. prop = [ab cd ef byte4: 00 ff fe];
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	e.g. str = start: "string value" end: ;
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File layout
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-----------
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Version 1 DTS files have the overall layout:
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	/dts-v1/;
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	[memory reservations]
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	/ {
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		[property definitions]
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		[child nodes]
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	};
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* The "/dts-v1/;" must be present to identify the file as a version 1
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  DTS (dts files without this tag will be treated by dtc as being in
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  the obsolete "version 0", which uses a different format for integers
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  amongst other small but incompatible changes).
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* Memory reservations define an entry for the device tree blob's
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  memory reservation table.  They have the form:
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	e.g. /memreserve/ <address> <length>;
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  Where <address> and <length> are 64-bit C-style integers.
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* The / { ... }; section defines the root node of the device tree.
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* C style (/* ... */) and C++ style (// ...) comments are supported.
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	-- David Gibson <david@gibson.dropbear.id.au>
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	-- Yoder Stuart <stuart.yoder@freescale.com>