033089f290
Elements of size 8, 16, 32, and 64 bits are supported. The new
/bits/ syntax was selected so as to not pollute the reserved
keyword space with uint8/uint16/... type names.
With this patch the following property assignment:
property = /bits/ 16 <0x1234 0x5678 0x0 0xffff>;
is equivalent to:
property = <0x12345678 0x0000ffff>;
It is now also possible to directly specify a 64 bit literal in a
cell list, also known as an array using:
property = /bits/ 64 <0xdeadbeef00000000>;
It is an error to attempt to store a literal into an element that is
too small to hold the literal, and the compiler will generate an
error when it detects this. For instance:
property = /bits/ 8 <256>;
Will fail to compile. It is also an error to attempt to place a
reference in a non 32-bit element.
The documentation has been changed to reflect that the cell list
is now an array of elements that can be of sizes other than the
default 32-bit cell size.
The sized_cells test tests the creation and access of 8, 16, 32,
and 64-bit sized elements. It also tests that the creation of two
properties, one with 16 bit elements and one with 32 bit elements
result in the same property contents.
Signed-off-by: Anton Staaf <robotboy@chromium.org>
Acked-by: David Gibson <david@gibson.dropbear.id.au>
122 lines
4.2 KiB
Text
122 lines
4.2 KiB
Text
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 8, 16, 32, or 64-bit integer
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elements, as NUL-terminated strings, as bytestrings or a combination of these.
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* Arrays are represented by angle brackets surrounding a space separated list
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of C-style integers or character literals. Array elements default to 32-bits
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in size. An array of 32-bit elements is also known as a cell list or a list
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of cells. A cell being an unsigned 32-bit integer.
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e.g. interrupts = <17 0xc>;
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* A 64-bit value can be represented with two 32-bit elements.
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e.g. clock-frequency = <0x00000001 0x00000000>;
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* The storage size of an element can be changed using the /bits/ prefix. The
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/bits/ prefix allows for the creation of 8, 16, 32, and 64-bit elements.
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The resulting array will not be padded to a multiple of the default 32-bit
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element size.
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e.g. interrupts = /bits/ 8 <17 0xc>;
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e.g. clock-frequency = /bits/ 64 <0x0000000100000000>;
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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 an array a reference to another node will be expanded to that node's
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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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References are only permitted in arrays that have an element size of
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32-bits.
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* Outside an array, a reference to another node will be expanded to that
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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 elements of an array, or between bytes of a 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>
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-- Anton Staaf <robotboy@chromium.org>
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