xref: /openbmc/linux/Documentation/devicetree/bindings/example-schema.yaml (revision 1ac731c529cd4d6adbce134754b51ff7d822b145)

# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
# Copyright 2018 Linaro Ltd.
%YAML 1.2
---
# All the top-level keys are standard json-schema keywords except for
# 'maintainers' and 'select'

# $id is a unique identifier based on the filename. There may or may not be a
# file present at the URL.
$id: http://devicetree.org/schemas/example-schema.yaml#
# $schema is the meta-schema this schema should be validated with.
$schema: http://devicetree.org/meta-schemas/core.yaml#

title: An Example Device

maintainers:
  - Rob Herring <robh@kernel.org>

description: |
  A more detailed multi-line description of the binding.

  Details about the hardware device and any links to datasheets can go here.

  Literal blocks are marked with the '|' at the beginning. The end is marked by
  indentation less than the first line of the literal block. Lines also cannot
  begin with a tab character.

select: false
  # 'select' is a schema applied to a DT node to determine if this binding
  # schema should be applied to the node. It is optional and by default the
  # possible compatible strings are extracted and used to match.

  # In this case, a 'false' schema will never match.

properties:
  # A dictionary of DT properties for this binding schema
  compatible:
    # More complicated schema can use oneOf (XOR), anyOf (OR), or allOf (AND)
    # to handle different conditions.
    # In this case, it's needed to handle a variable number of values as there
    # isn't another way to express a constraint of the last string value.
    # The boolean schema must be a list of schemas.
    oneOf:
      - items:
          # items is a list of possible values for the property. The number of
          # values is determined by the number of elements in the list.
          # Order in lists is significant, order in dicts is not
          # Must be one of the 1st enums followed by the 2nd enum
          #
          # Each element in items should be 'enum' or 'const'
          - enum:
              - vendor,soc4-ip
              - vendor,soc3-ip
              - vendor,soc2-ip
          - const: vendor,soc1-ip
        # additionalItems being false is implied
        # minItems/maxItems equal to 2 is implied
      - items:
          # 'const' is just a special case of an enum with a single possible value
          - const: vendor,soc1-ip

  reg:
    # The core schema already checks that reg values are numbers, so device
    # specific schema don't need to do those checks.
    # The description of each element defines the order and implicitly defines
    # the number of reg entries.
    items:
      - description: core registers
      - description: aux registers
    # minItems/maxItems equal to 2 is implied

  reg-names:
    # The core schema enforces this (*-names) is a string array
    items:
      - const: core
      - const: aux

  clocks:
    # Cases that have only a single entry just need to express that with maxItems
    maxItems: 1
    description: bus clock. A description is only needed for a single item if
      there's something unique to add.
      The items should have a fixed order, so pattern matching names are
      discouraged.

  clock-names:
    # For single-entry lists in clocks, resets etc., the xxx-names often do not
    # bring any value, especially if they copy the IP block name.  In such case
    # just skip the xxx-names.
    items:
      - const: bus

  interrupts:
    # Either 1 or 2 interrupts can be present
    minItems: 1
    items:
      - description: tx or combined interrupt
      - description: rx interrupt
    description:
      A variable number of interrupts warrants a description of what conditions
      affect the number of interrupts. Otherwise, descriptions on standard
      properties are not necessary.
      The items should have a fixed order, so pattern matching names are
      discouraged.

  interrupt-names:
    # minItems must be specified here because the default would be 2
    minItems: 1
    items:
      - const: tx irq
      - const: rx irq

  # Property names starting with '#' must be quoted
  '#interrupt-cells':
    # A simple case where the value must always be '2'.
    # The core schema handles that this must be a single integer.
    const: 2

  interrupt-controller: true
    # The core checks this is a boolean, so just have to list it here to be
    # valid for this binding.

  clock-frequency:
    # The type is set in the core schema. Per-device schema only need to set
    # constraints on the possible values.
    minimum: 100
    maximum: 400000
    # The value that should be used if the property is not present
    default: 200

  foo-gpios:
    maxItems: 1
    description: A connection of the 'foo' gpio line.

  # *-supply is always a single phandle, so nothing more to define.
  foo-supply: true

  # Vendor-specific properties
  #
  # Vendor-specific properties have slightly different schema requirements than
  # common properties. They must have at least a type definition and
  # 'description'.
  vendor,int-property:
    description: Vendor-specific properties must have a description
    $ref: /schemas/types.yaml#/definitions/uint32
    enum: [2, 4, 6, 8, 10]

  vendor,bool-property:
    description: Vendor-specific properties must have a description. Boolean
      properties are one case where the json-schema 'type' keyword can be used
      directly.
    type: boolean

  vendor,string-array-property:
    description: Vendor-specific properties should reference a type in the
      core schema.
    $ref: /schemas/types.yaml#/definitions/string-array
    items:
      - enum: [foo, bar]
      - enum: [baz, boo]

  vendor,property-in-standard-units-microvolt:
    description: Vendor-specific properties having a standard unit suffix
      don't need a type.
    enum: [ 100, 200, 300 ]

  vendor,int-array-variable-length-and-constrained-values:
    description: Array might define what type of elements might be used (e.g.
      their range).
    $ref: /schemas/types.yaml#/definitions/uint32-array
    minItems: 2
    maxItems: 3
    items:
      minimum: 0
      maximum: 8

  child-node:
    description: Child nodes are just another property from a json-schema
      perspective.
    type: object  # DT nodes are json objects
    # Child nodes also need additionalProperties or unevaluatedProperties
    additionalProperties: false
    properties:
      vendor,a-child-node-property:
        description: Child node properties have all the same schema
          requirements.
        type: boolean

    required:
      - vendor,a-child-node-property

# Describe the relationship between different properties
dependencies:
  # 'vendor,bool-property' is only allowed when 'vendor,string-array-property'
  # is present
  vendor,bool-property: [ 'vendor,string-array-property' ]
  # Expressing 2 properties in both orders means all of the set of properties
  # must be present or none of them.
  vendor,string-array-property: [ 'vendor,bool-property' ]

required:
  - compatible
  - reg
  - interrupts
  - interrupt-controller

# if/then schema can be used to handle conditions on a property affecting
# another property. A typical case is a specific 'compatible' value changes the
# constraints on other properties.
#
# For multiple 'if' schema, group them under an 'allOf'.
#
# If the conditionals become too unweldy, then it may be better to just split
# the binding into separate schema documents.
allOf:
  - if:
      properties:
        compatible:
          contains:
            const: vendor,soc2-ip
    then:
      required:
        - foo-supply
    else:
      # If otherwise the property is not allowed:
      properties:
        foo-supply: false
  # Altering schema depending on presence of properties is usually done by
  # dependencies (see above), however some adjustments might require if:
  - if:
      required:
        - vendor,bool-property
    then:
      properties:
        vendor,int-property:
          enum: [2, 4, 6]

# Ideally, the schema should have this line otherwise any other properties
# present are allowed. There's a few common properties such as 'status' and
# 'pinctrl-*' which are added automatically by the tooling.
#
# This can't be used in cases where another schema is referenced
# (i.e. allOf: [{$ref: ...}]).
# If and only if another schema is referenced and arbitrary children nodes can
# appear, "unevaluatedProperties: false" could be used.  A typical example is
# an I2C controller where no name pattern matching for children can be added.
additionalProperties: false

examples:
  # Examples are now compiled with dtc and validated against the schemas
  #
  # Examples have a default #address-cells and #size-cells value of 1. This can
  # be overridden or an appropriate parent bus node should be shown (such as on
  # i2c buses).
  #
  # Any includes used have to be explicitly included. Use 4-space indentation.
  - |
    node@1000 {
        compatible = "vendor,soc4-ip", "vendor,soc1-ip";
        reg = <0x1000 0x80>,
              <0x3000 0x80>;
        reg-names = "core", "aux";
        interrupts = <10>;
        interrupt-controller;
    };