linux-stable/Documentation/devicetree/bindings/example-schema.yaml
Krzysztof Kozlowski 7a150b0d85 docs: dt: writing-schema: mention coding style
Mention the usage of YAML coding style.  Describe explicitly that
four-space indentation in DTS examples is preferred, because:
1. The YAML's default two-space indentation for DTS code makes it
   significantly less readable.
2. Linux coding style tabs would introduce inconsistency (entire file is
   indented with spaces).
3. On the other hand, eight spaces would not align with example's
   opening '  - |' part.  Four spaces makes the code nicely aligned with
   it.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220403081849.8051-2-krzysztof.kozlowski@linaro.org
2022-04-04 19:55:03 -05:00

261 lines
8.7 KiB
YAML

# 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 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 (*-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:
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).
$ref: /schemas/types.yaml#/definitions/uint32-array
minItems: 2
maxItems: 3
items:
minimum: 0
maximum: 8
child-node:
description: Child nodes are just another property from a json-schema
perspective.
type: object # DT nodes are json objects
properties:
vendor,a-child-node-property:
description: Child node properties have all the same schema
requirements.
type: boolean
required:
- vendor,a-child-node-property
# Describe the relationship between different properties
dependencies:
# 'vendor,bool-property' is only allowed when 'vendor,string-array-property'
# is present
vendor,bool-property: [ 'vendor,string-array-property' ]
# Expressing 2 properties in both orders means all of the set of properties
# must be present or none of them.
vendor,string-array-property: [ 'vendor,bool-property' ]
required:
- compatible
- reg
- interrupts
- interrupt-controller
# if/then schema can be used to handle conditions on a property affecting
# another property. A typical case is a specific 'compatible' value changes the
# constraints on other properties.
#
# For multiple 'if' schema, group them under an 'allOf'.
#
# If the conditionals become too unweldy, then it may be better to just split
# the binding into separate schema documents.
allOf:
- if:
properties:
compatible:
contains:
const: vendor,soc2-ip
then:
required:
- foo-supply
else:
# If otherwise the property is not allowed:
properties:
foo-supply: false
# Altering schema depending on presence of properties is usually done by
# dependencies (see above), however some adjustments might require if:
- if:
required:
- vendor,bool-property
then:
properties:
vendor,int-property:
enum: [2, 4, 6]
# Ideally, the schema should have this line otherwise any other properties
# present are allowed. There's a few common properties such as 'status' and
# 'pinctrl-*' which are added automatically by the tooling.
#
# This can't be used in cases where another schema is referenced
# (i.e. allOf: [{$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;
};