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This is joint work with Kumar Gala (see signed-off-by). Document the changes to the generated node macros in macros.bnf, moving the old file to legacy-macros.bnf and putting it in its own section. The actual generated macros are now a low-level detail, so rewrite the foregoing sections as examples in terms of the new <devicetree.h> APIs. Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no> Signed-off-by: Kumar Gala <kumar.gala@linaro.org>
152 lines
4.0 KiB
ReStructuredText
152 lines
4.0 KiB
ReStructuredText
.. _dt-bindings:
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Devicetree bindings
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###################
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A devicetree on its own is only half the story for describing hardware. The
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devicetree format itself is relatively unstructured, and doesn't tell the
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:ref:`build system <build_overview>` which pieces of information in a
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particular devicetree are useful to :ref:`device drivers <device_model_api>` or
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:ref:`applications <application>`.
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*Devicetree bindings* provide the other half of this information. Zephyr
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devicetree bindings are YAML files in a custom format (Zephyr does not use the
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dt-schema tools used by the Linux kernel). The build system uses bindings
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when generating code for :ref:`dt-from-c`.
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.. _dt-binding-compat:
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Mapping nodes to bindings
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*************************
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During the :ref:`build_configuration_phase`, the build system tries to map each
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node in the devicetree to a binding file. The build system only generates
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macros for devicetree nodes which have matching bindings. Nodes are mapped to
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bindings by their :ref:`compatible properties <dt-syntax>`. Take the following
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node as an example:
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.. code-block:: DTS
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bar-device {
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compatible = "foo-company,bar-device";
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/* ... */
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};
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The build system will try to map the ``bar-device`` node to a YAML binding with
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this ``compatible:`` line:
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.. code-block:: yaml
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compatible: "foo-company,bar-device"
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Built-in bindings are stored in :zephyr_file:`dts/bindings/`. Binding file
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names usually match their ``compatible:`` lines, so the above binding would be
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named :file:`foo-company,bar-device.yaml`.
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If a node has more than one string in its ``compatible`` property, the build
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system looks for compatible bindings in the listed order and uses the first
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match. Take this node as an example:
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.. code-block:: DTS
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baz-device {
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compatible = "foo-company,baz-device", "generic-baz-device";
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};
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The ``baz-device`` node would get mapped to the binding for compatible
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``"generic-baz-device"`` if the build system can't find a binding for
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``"foo-company,baz-device"``.
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Nodes without compatible properties can be mapped to bindings associated with
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their parent nodes. For an example, see the ``pwmleds`` node in the bindings
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file format described below.
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If a node describes hardware on a bus, like I2C or SPI, then the bus type is
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also taken into account when mapping nodes to bindings. See the comments near
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``on-bus:`` in the bindings syntax for details.
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Bindings file syntax
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********************
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Below is a template that shows the Zephyr bindings file syntax. It is stored in
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:zephyr_file:`dts/binding-template.yaml`.
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.. literalinclude:: ../../../dts/binding-template.yaml
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:language: yaml
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.. _legacy_binding_syntax:
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Legacy bindings syntax
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**********************
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The bindings syntax described above was introduced in the Zephyr 2.1 release.
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This section describes how to update bindings written in the legacy syntax,
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starting with this example written in the legacy syntax.
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.. code-block:: yaml
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title: ...
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description: ...
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inherits:
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!include foo.yaml
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parent:
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bus: spi
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parent-bus: spi
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properties:
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compatible:
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constraint: "company,device"
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type: string-array
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frequency:
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type: int
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category: optional
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sub-node:
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properties:
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child-prop:
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type: int
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category: required
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# Assume this is a binding for an interrupt controller
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"#cells":
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- irq
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- priority
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- flags
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This should now be written like this:
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.. code-block:: yaml
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description: ...
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compatible: "company,device"
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include: foo.yaml
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bus: spi
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properties:
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frequency:
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type: int
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required: false
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child-binding:
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description: ...
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properties:
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child-prop:
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type: int
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required: true
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interrupt-cells:
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- irq
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- priority
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- cells
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The legacy syntax is still supported for backwards compatibility, but generates
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deprecation warnings. Support will be dropped in the Zephyr 2.3 release.
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