devicetree/bindings/writing-schema.rst

1 .. SPDX-License-Identifier: GPL-2.0
3 Writing Devicetree Bindings in json-schema
6 Devicetree bindings are written using json-schema vocabulary. Schema files are
7 written in a JSON-compatible subset of YAML. YAML is used instead of JSON as it
11 Also see :ref:`example-schema`.
14 ---------------
16 Each schema doc is a structured json-schema which is defined by a set of
17 top-level properties. Generally, there is one binding defined per file. The
18 top-level json-schema properties used are:
21   A json-schema unique identifier string. The string must be a valid
22   URI typically containing the binding's filename and path. For DT schema, it must
31   Indicates the meta-schema the schema file adheres to.
34   A one-line description on the contents of the binding schema.
37   A DT specific property. Contains a list of email address(es)
41   Optional. A multi-line text block containing any detailed
47   Optional. A json-schema used to match nodes for applying the
49   compatible-string values or node name. Most bindings should not need select.
57   A set of sub-schema defining all the DT properties for the
59   common properties (e.g. 'interrupts') or are binding/vendor-specific
62 A property can also define a child DT node with child properties defined
65 For more details on properties sections, see 'Property Schema' section.
71   A list of DT properties from the 'properties' section that
80 Property Schema
81 ---------------
83 The 'properties' section of the schema contains all the DT properties for a
84 binding. Each property contains a set of constraints using json-schema
85 vocabulary for that property. The properties schemas are what are used for
86 validation of DT files.
92 Vendor-specific properties will typically need more detailed schema. With the
94 schemas/types.yaml. A "description" property is always required.
96 The Devicetree schemas don't exactly match the YAML-encoded DT data produced by
101 The default for arrays in json-schema is they are variable-sized and allow more
112 ------------
114 Use YAML coding style (two-space indentation). For DTS examples in the schema,
115 preferred is four-space indentation.
118 -------
123 The DT schema project must be installed in order to validate the DT schema
124 binding documents and validate DTS files using the DT schema. The DT schema
132     apt install swig python3-dev
134 Several executables (dt-doc-validate, dt-mk-schema, dt-validate) will be
142 The DT schema binding documents must be validated using the meta-schema (the
143 schema for the schema) to ensure they are both valid json-schema and valid
144 binding schema. All of the DT binding documents can be validated using the
149 In order to perform validation of DT source files, use the ``dtbs_check`` target::
166     make dt_binding_check DT_SCHEMA_FILES=trivial-devices.yaml
168     make dtbs_check DT_SCHEMA_FILES=trivial-devices.yaml
171 json-schema Resources
172 ---------------------
175 `JSON-Schema Specifications <http://json-schema.org/>`_
179 .. _example-schema:
182 ------------------------
184 Also available as a separate file: :download:`example-schema.yaml`
186 .. literalinclude:: example-schema.yaml