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-:orphan:
-
-Writing DeviceTree Bindings in json-schema
-==========================================
-
-Devicetree bindings are written using json-schema vocabulary. Schema files are
-written in a JSON compatible subset of YAML. YAML is used instead of JSON as it
-considered more human readable and has some advantages such as allowing
-comments (Prefixed with '#').
-
-Schema Contents
----------------
-
-Each schema doc is a structured json-schema which is defined by a set of
-top-level properties. Generally, there is one binding defined per file. The
-top-level json-schema properties used are:
-
-$id
- A json-schema unique identifier string. The string must be a valid
- URI typically containing the binding's filename and path. For DT schema, it must
- begin with "http://devicetree.org/schemas/". The URL is used in constructing
- references to other files specified in schema "$ref" properties. A $ref values
- with a leading '/' will have the hostname prepended. A $ref value a relative
- path or filename only will be prepended with the hostname and path components
- of the current schema file's '$id' value. A URL is used even for local files,
- but there may not actually be files present at those locations.
-
-$schema
- Indicates the meta-schema the schema file adheres to.
-
-title
- A one line description on the contents of the binding schema.
-
-maintainers
- A DT specific property. Contains a list of email address(es)
- for maintainers of this binding.
-
-description
- Optional. A multi-line text block containing any detailed
- information about this binding. It should contain things such as what the block
- or device does, standards the device conforms to, and links to datasheets for
- more information.
-
-select
- Optional. A json-schema used to match nodes for applying the
- schema. By default without 'select', nodes are matched against their possible
- compatible string values or node name. Most bindings should not need select.
-
- allOf
- Optional. A list of other schemas to include. This is used to
- include other schemas the binding conforms to. This may be schemas for a
- particular class of devices such as I2C or SPI controllers.
-
- properties
- A set of sub-schema defining all the DT properties for the
- binding. The exact schema syntax depends on whether properties are known,
- common properties (e.g. 'interrupts') or are binding/vendor specific properties.
-
-A property can also define a child DT node with child properties defined
-under it.
-
-For more details on properties sections, see 'Property Schema' section.
-
-patternProperties
- Optional. Similar to 'properties', but names are regex.
-
-required
- A list of DT properties from the 'properties' section that
- must always be present.
-
-examples
- Optional. A list of one or more DTS hunks implementing the
- binding. Note: YAML doesn't allow leading tabs, so spaces must be used instead.
-
-Unless noted otherwise, all properties are required.
-
-Property Schema
----------------
-
-The 'properties' section of the schema contains all the DT properties for a
-binding. Each property contains a set of constraints using json-schema
-vocabulary for that property. The properties schemas are what is used for
-validation of DT files.
-
-For common properties, only additional constraints not covered by the common
-binding schema need to be defined such as how many values are valid or what
-possible values are valid.
-
-Vendor specific properties will typically need more detailed schema. With the
-exception of boolean properties, they should have a reference to a type in
-schemas/types.yaml. A "description" property is always required.
-
-The Devicetree schemas don't exactly match the YAML encoded DT data produced by
-dtc. They are simplified to make them more compact and avoid a bunch of
-boilerplate. The tools process the schema files to produce the final schema for
-validation. There are currently 2 transformations the tools perform.
-
-The default for arrays in json-schema is they are variable sized and allow more
-entries than explicitly defined. This can be restricted by defining 'minItems',
-'maxItems', and 'additionalItems'. However, for DeviceTree Schemas, a fixed
-size is desired in most cases, so these properties are added based on the
-number of entries in an 'items' list.
-
-The YAML Devicetree format also makes all string values an array and scalar
-values a matrix (in order to define groupings) even when only a single value
-is present. Single entries in schemas are fixed up to match this encoding.
-
-Testing
--------
-
-Dependencies
-~~~~~~~~~~~~
-
-The DT schema project must be installed in order to validate the DT schema
-binding documents and validate DTS files using the DT schema. The DT schema
-project can be installed with pip::
-
- pip3 install git+https://github.com/devicetree-org/dt-schema.git@master
-
-Several executables (dt-doc-validate, dt-mk-schema, dt-validate) will be
-installed. Ensure they are in your PATH (~/.local/bin by default).
-
-dtc must also be built with YAML output support enabled. This requires that
-libyaml and its headers be installed on the host system.
-
-Running checks
-~~~~~~~~~~~~~~
-
-The DT schema binding documents must be validated using the meta-schema (the
-schema for the schema) to ensure they are both valid json-schema and valid
-binding schema. All of the DT binding documents can be validated using the
-``dt_binding_check`` target::
-
- make dt_binding_check
-
-In order to perform validation of DT source files, use the ``dtbs_check`` target::
-
- make dtbs_check
-
-Note that ``dtbs_check`` will skip any binding schema files with errors. It is
-necessary to use ``dt_binding_check`` to get all the validation errors in the
-binding schema files.
-
-It is also possible to run checks with a single schema file by setting the
-``DT_SCHEMA_FILES`` variable to a specific schema file.
-
-::
-
- make dt_binding_check DT_SCHEMA_FILES=Documentation/devicetree/bindings/trivial-devices.yaml
- make dtbs_check DT_SCHEMA_FILES=Documentation/devicetree/bindings/trivial-devices.yaml
-
-
-json-schema Resources
----------------------
-
-
-`JSON-Schema Specifications <http://json-schema.org/>`_
-
-`Using JSON Schema Book <http://usingjsonschema.com/>`_