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`.
13 Schema Contents
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
24   references to other files specified in schema "$ref" properties. A $ref value
27   components of the current schema file's '$id' value. A URL is used even for
30 $schema
31   Indicates the meta-schema the schema file adheres to.
34   A one-line description of the hardware being described in 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
48   schema. By default, without 'select', nodes are matched against their possible
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
58   binding. The exact schema syntax depends on whether properties are known,
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
75   Keywords controlling how schema will validate properties not matched by this
76   schema's 'properties' or 'patternProperties'. Each schema is supposed to
77   have exactly one of these keywords in top-level part, so either
82       Most common case, where no additional schema is referenced or if this
86       Used when this binding references other schema whose all properties
92       'unevaluatedProperties: false'.  Typically bus or common-part schemas.
102 Property Schema
103 ---------------
105 The 'properties' section of the schema contains all the DT properties for a
106 binding. Each property contains a set of constraints using json-schema
108 validation of DT files.
111 binding schema need to be defined such as how many values are valid or what
114 Vendor-specific properties will typically need more detailed schema. With the
118 The Devicetree schemas don't exactly match the YAML-encoded DT data produced by
120 boilerplate. The tools process the schema files to produce the final schema for
123 The default for arrays in json-schema is they are variable-sized and allow more
134 ------------
136 Use YAML coding style (two-space indentation). For DTS examples in the schema,
137 preferred is four-space indentation.
140 -------
145 The DT schema project must be installed in order to validate the DT schema
146 binding documents and validate DTS files using the DT schema. The DT schema
154     apt install swig python3-dev
156 Several executables (dt-doc-validate, dt-mk-schema, dt-validate) will be
164 The DT schema binding documents must be validated using the meta-schema (the
165 schema for the schema) to ensure they are both valid json-schema and valid
166 binding schema. All of the DT binding documents can be validated using the
171 In order to perform validation of DT source files, use the ``dtbs_check`` target::
175 Note that ``dtbs_check`` will skip any binding schema files with errors. It is
177 binding schema files.
183 It is also possible to run checks with a subset of matching schema files by
184 setting the ``DT_SCHEMA_FILES`` variable to 1 or more specific schema files or
190     make dt_binding_check DT_SCHEMA_FILES=trivial-devices.yaml
191     make dt_binding_check DT_SCHEMA_FILES=trivial-devices.yaml:rtc.yaml
193     make dtbs_check DT_SCHEMA_FILES=trivial-devices.yaml
196 json-schema Resources
197 ---------------------
200 `JSON-Schema Specifications <http://json-schema.org/>`_
202 `Using JSON Schema Book <http://usingjsonschema.com/>`_
204 .. _example-schema:
206 Annotated Example Schema
207 ------------------------
209 Also available as a separate file: :download:`example-schema.yaml`
211 .. literalinclude:: example-schema.yaml