linux/linux-5.4.31/Documentation/devicetree/bindings/example-schema.yaml

# SPDX-License-Identifier: (GPL-2.0 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 schema annotated with jsonschema details

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
          - enum:
              - 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 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

  clock-names:
    items:
      - const: bus

  interrupts:
    # Either 1 or 2 interrupts can be present
    minItems: 1
    maxItems: 2
    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.

  interrupt-names:
    # minItems must be specified here because the default would be 2
    minItems: 1
    maxItems: 2
    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.

  vendor,int-property:
    description: Vendor specific properties must have a description
    # 'allOf' is the json-schema way of subclassing a schema. Here the base
    # type schema is referenced and then additional constraints on the values
    # are added.
    allOf:
      - $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 is 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.
    allOf:
      - $ref: /schemas/types.yaml#/definitions/string-array
      - items:
          - enum: [ foo, bar ]
          - enum: [ baz, boo ]

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

examples:
  # Examples are now compiled with dtc
  - |
    node@1000 {
          compatible = "vendor,soc4-ip", "vendor,soc1-ip";
          reg = <0x1000 0x80>,
                <0x3000 0x80>;
          reg-names = "core", "aux";
          interrupts = <10>;
          interrupt-controller;
    };