xref: /linux/Documentation/devicetree/bindings/example-schema.yaml (revision 88872790923e2d80edf29a00b4e440f1473fa8f5) 
1# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
2# Copyright 2018 Linaro Ltd.
3%YAML 1.2
4---
5# All the top-level keys are standard json-schema keywords except for
6# 'maintainers' and 'select'
7
8# $id is a unique identifier based on the filename. There may or may not be a
9# file present at the URL.
10$id: http://devicetree.org/schemas/example-schema.yaml#
11# $schema is the meta-schema this schema should be validated with.
12$schema: http://devicetree.org/meta-schemas/core.yaml#
13
14title: An Example Device
15
16maintainers:
17  - Rob Herring <robh@kernel.org>
18
19description: |
20  A more detailed multi-line description of the binding.
21
22  Details about the hardware device and any links to datasheets can go here.
23
24  Literal blocks are marked with the '|' at the beginning. The end is marked by
25  indentation less than the first line of the literal block. Lines also cannot
26  begin with a tab character.
27
28select: false
29  # 'select' is a schema applied to a DT node to determine if this binding
30  # schema should be applied to the node. It is optional and by default the
31  # possible compatible strings are extracted and used to match.
32
33  # In this case, a 'false' schema will never match.
34
35properties:
36  # A dictionary of DT properties for this binding schema
37  compatible:
38    # More complicated schema can use oneOf (XOR), anyOf (OR), or allOf (AND)
39    # to handle different conditions.
40    # In this case, it's needed to handle a variable number of values as there
41    # isn't another way to express a constraint of the last string value.
42    # The boolean schema must be a list of schemas.
43    oneOf:
44      - items:
45          # items is a list of possible values for the property. The number of
46          # values is determined by the number of elements in the list.
47          # Order in lists is significant, order in dicts is not
48          # Must be one of the 1st enums followed by the 2nd enum
49          #
50          # Each element in items should be 'enum' or 'const'
51          - enum:
52              - vendor,soc4-ip
53              - vendor,soc3-ip
54              - vendor,soc2-ip
55          - const: vendor,soc1-ip
56        # additionalItems being false is implied
57        # minItems/maxItems equal to 2 is implied
58      - items:
59          # 'const' is just a special case of an enum with a single possible value
60          - const: vendor,soc1-ip
61
62  reg:
63    # The core schema already checks that reg values are numbers, so device
64    # specific schema don't need to do those checks.
65    # The description of each element defines the order and implicitly defines
66    # the number of reg entries.
67    items:
68      - description: core registers
69      - description: aux registers
70    # minItems/maxItems equal to 2 is implied
71
72  reg-names:
73    # The core schema enforces this (*-names) is a string array
74    items:
75      - const: core
76      - const: aux
77
78  clocks:
79    # Cases that have only a single entry just need to express that with maxItems
80    maxItems: 1
81    description: bus clock. A description is only needed for a single item if
82      there's something unique to add.
83      The items should have a fixed order, so pattern matching names are
84      discouraged.
85
86  clock-names:
87    # For single-entry lists in clocks, resets etc., the xxx-names often do not
88    # bring any value, especially if they copy the IP block name.  In such case
89    # just skip the xxx-names.
90    items:
91      - const: bus
92
93  interrupts:
94    # Either 1 or 2 interrupts can be present
95    minItems: 1
96    items:
97      - description: tx or combined interrupt
98      - description: rx interrupt
99    description:
100      A variable number of interrupts warrants a description of what conditions
101      affect the number of interrupts. Otherwise, descriptions on standard
102      properties are not necessary.
103      The items should have a fixed order, so pattern matching names are
104      discouraged.
105
106  interrupt-names:
107    # minItems must be specified here because the default would be 2
108    minItems: 1
109    items:
110      - const: tx irq
111      - const: rx irq
112
113  # Property names starting with '#' must be quoted
114  '#interrupt-cells':
115    # A simple case where the value must always be '2'.
116    # The core schema handles that this must be a single integer.
117    const: 2
118
119  interrupt-controller: true
120    # The core checks this is a boolean, so just have to list it here to be
121    # valid for this binding.
122
123  clock-frequency:
124    # The type is set in the core schema. Per-device schema only need to set
125    # constraints on the possible values.
126    minimum: 100
127    maximum: 400000
128    # The value that should be used if the property is not present
129    default: 200
130
131  foo-gpios:
132    maxItems: 1
133    description: A connection of the 'foo' gpio line.
134
135  # *-supply is always a single phandle, so nothing more to define.
136  foo-supply: true
137
138  # Vendor-specific properties
139  #
140  # Vendor-specific properties have slightly different schema requirements than
141  # common properties. They must have at least a type definition and
142  # 'description'.
143  vendor,int-property:
144    description: Vendor-specific properties must have a description
145    $ref: /schemas/types.yaml#/definitions/uint32
146    enum: [2, 4, 6, 8, 10]
147
148  vendor,bool-property:
149    description: Vendor-specific properties must have a description. Boolean
150      properties are one case where the json-schema 'type' keyword can be used
151      directly.
152    type: boolean
153
154  vendor,string-array-property:
155    description: Vendor-specific properties should reference a type in the
156      core schema.
157    $ref: /schemas/types.yaml#/definitions/string-array
158    items:
159      - enum: [foo, bar]
160      - enum: [baz, boo]
161
162  vendor,property-in-standard-units-microvolt:
163    description: Vendor-specific properties having a standard unit suffix
164      don't need a type.
165    enum: [ 100, 200, 300 ]
166
167  vendor,int-array-variable-length-and-constrained-values:
168    description: Array might define what type of elements might be used (e.g.
169      their range).
170    $ref: /schemas/types.yaml#/definitions/uint32-array
171    minItems: 2
172    maxItems: 3
173    items:
174      minimum: 0
175      maximum: 8
176
177  child-node:
178    description: Child nodes are just another property from a json-schema
179      perspective.
180    type: object  # DT nodes are json objects
181    # Child nodes also need additionalProperties or unevaluatedProperties
182    additionalProperties: false
183    properties:
184      vendor,a-child-node-property:
185        description: Child node properties have all the same schema
186          requirements.
187        type: boolean
188
189    required:
190      - vendor,a-child-node-property
191
192# Describe the relationship between different properties
193dependencies:
194  # 'vendor,bool-property' is only allowed when 'vendor,string-array-property'
195  # is present
196  vendor,bool-property: [ 'vendor,string-array-property' ]
197  # Expressing 2 properties in both orders means all of the set of properties
198  # must be present or none of them.
199  vendor,string-array-property: [ 'vendor,bool-property' ]
200
201required:
202  - compatible
203  - reg
204  - interrupts
205  - interrupt-controller
206
207# if/then schema can be used to handle conditions on a property affecting
208# another property. A typical case is a specific 'compatible' value changes the
209# constraints on other properties.
210#
211# For multiple 'if' schema, group them under an 'allOf'.
212#
213# If the conditionals become too unweldy, then it may be better to just split
214# the binding into separate schema documents.
215allOf:
216  - if:
217      properties:
218        compatible:
219          contains:
220            const: vendor,soc2-ip
221    then:
222      required:
223        - foo-supply
224    else:
225      # If otherwise the property is not allowed:
226      properties:
227        foo-supply: false
228  # Altering schema depending on presence of properties is usually done by
229  # dependencies (see above), however some adjustments might require if:
230  - if:
231      required:
232        - vendor,bool-property
233    then:
234      properties:
235        vendor,int-property:
236          enum: [2, 4, 6]
237
238# Ideally, the schema should have this line otherwise any other properties
239# present are allowed. There's a few common properties such as 'status' and
240# 'pinctrl-*' which are added automatically by the tooling.
241#
242# This can't be used in cases where another schema is referenced
243# (i.e. allOf: [{$ref: ...}]).
244# If and only if another schema is referenced and arbitrary children nodes can
245# appear, "unevaluatedProperties: false" could be used.  A typical example is
246# an I2C controller where no name pattern matching for children can be added.
247additionalProperties: false
248
249examples:
250  # Examples are now compiled with dtc and validated against the schemas
251  #
252  # Examples have a default #address-cells and #size-cells value of 1. This can
253  # be overridden or an appropriate parent bus node should be shown (such as on
254  # i2c buses).
255  #
256  # Any includes used have to be explicitly included. Use 4-space indentation.
257  - |
258    node@1000 {
259        compatible = "vendor,soc4-ip", "vendor,soc1-ip";
260        reg = <0x1000 0x80>,
261              <0x3000 0x80>;
262        reg-names = "core", "aux";
263        interrupts = <10>;
264        interrupt-controller;
265    };
266