Boot Linux faster!

Check our new training course

Boot Linux faster!

Check our new training course
and Creative Commons CC-BY-SA
lecture and lab materials

Bootlin logo

Elixir Cross Referencer

description: |
    Free-form description of the device/node. Can have multiple
    lines/paragraphs.

    See https://yaml-multiline.info/ for formatting help.

# Used to map nodes to bindings
compatible: "manufacturer,device"

# The 'compatible' above would match this node:
#
#     device {
#         compatible = "manufacturer,device";
#         ...
#     };
#
# Assuming no binding has 'compatible: "manufacturer,device-v2"', it would also
# match this node:
#
#     device {
#         compatible = "manufacturer,device-v2", "manufacturer,device";
#         ...
#     };
#
# Strings in 'compatible' properties on nodes are tried from left to right, and
# the first binding found is used.
#
# If more than one binding for a compatible is found, an error is raised.

# Bindings can include other files, which can be used to share common
# definitions between bindings.
#
# Included files are merged into bindings with a simple recursive dictionary
# merge. It is up to the binding author to make sure that the final merged
# binding is well-formed, though it is checked by the code as well.
#
# It is an error if a key appears with a different value in a binding and in a
# file it includes, with one exception: A binding can have 'required: true' for
# some property for which the included file has 'required: false' (see the
# description of 'properties' below). The 'required: true' from the binding
# takes precedence, allowing bindings to strengthen requirements from included
# files.
#
# Note that weakening requirements by having 'required: false' where the
# included file has 'required: true' is an error. This is meant to keep the
# organization clean.
#
# The file base.yaml contains definitions for many common properties. When
# writing a new binding, it is a good idea to check if base.yaml already
# defines some of the needed properties, and including it in that case. Note
# that you can make a property defined in base.yaml obligatory like this
# (taking 'reg' as an example):
#
#     reg:
#         required: true
#
# This relies on the dictionary merge to fill in the other keys for 'reg', like
# 'type'.
#
# When including multiple files, any overlapping 'required' keys on properties
# in the included files are ORed together. This makes sure that a
# 'required: true' is always respected.
include: other.yaml # or [other1.yaml, other2.yaml]

# If the node describes a bus, then the bus type should be given, like below
bus: <string describing bus type, e.g. "i2c">

# If the node appears on a bus, then the bus type should be given, like below.
#
# When looking for a binding for a node, the code checks if the binding for the
# parent node contains 'bus: <bus type>'. If it does, then only bindings with a
# matching 'on-bus: <bus type>' and bindings without an explicit 'on-bus'
# are considered. Bindings with an explicit 'on-bus: <bus type>' are looked
# for first, and if none is found bindings without an explicit `on-bus` are
# attempted. These two tests are done for each item in the `compatible` array
# in the order specified. This allows the same type of device to have different
# bindings depending on what bus it appears on.
on-bus: <string describing bus type, e.g. "i2c">

# 'properties' describes properties on the node, e.g.
#
#   reg = <1 2>;
#   current-speed = <115200>;
#   label = "foo";
#
# This is used to check that required properties appear, and to
# control the format of output generated for them. Except for some
# special-cased properties like 'reg', only properties listed here will
# generate output.
#
# A typical property entry looks like this:
#
#   <property name>:
#     deprecated: <true | false>
#     required: <true | false>
#     type: <string | int | boolean | array | uint8-array | string-array |
#            phandle | phandles | phandle-array | path | compound>
#     description: <description of the property>
#     enum:
#       - <item1>
#       - <item2>
#       ...
#       - <itemN>
#     const: <string | int>
#     default: <default>
#
# These types are available:
#
#   - 'type: string' is for properties that are assigned a single string, like
#
#         ident = "foo";
#
#   - 'type: int' is for properties that are assigned a single 32-bit value,
#     like
#
#         frequency = <100>;
#
#   - 'type: boolean' is for properties used as flags that don't take a value,
#     like
#
#         hw-flow-control;
#
#     The macro generated for the property gets set to 1 if the property exists
#     on the node, and to 0 otherwise. When combined with 'required: true',
#     this type just forces the flag to appear on the node. The output will
#     always be 1 in that case.
#
#     Warning: Since a macro is always generated for 'type: boolean'
#     properties, don't use #ifdef in tests. Do this instead:
#
#         #if DT_SOME_BOOLEAN_PROP == 1
#
#   - 'type: array' is for properties that are assigned zero or more 32-bit
#     values, like
#
#         pin-config = <1 2 3>;
#
#   - 'type: uint8-array' is for properties that are assigned zero or more
#     bytes with the [] syntax, like
#
#         lookup-table = [89 AB CD EF];
#
#     Each byte is given in hex.
#
#     This type is called 'bytestring' in the Devicetree specification.
#
#   - 'type: string-array' if for properties that are assigned zero or more
#     strings, like
#
#         idents = "foo", "bar", "baz";
#
#   - 'type: phandle' is for properties that are assigned a single phandle,
#     like
#
#         foo = <&label>;
#
#   - 'type: phandles' is for properties that are assigned zero or more
#     phandles, like
#
#         foo = <&label1 &label2 ...>;
#
#   - 'type: phandle-array' is for properties that take a list of phandles and
#     (possibly) 32-bit numbers, like
#
#         pwms = <&ctrl-1 1 2 &ctrl-2 3 4>;
#
#     This type requires that the property works in the standard way that
#     devicetree properties like pwms, clocks, *-gpios, and io-channels work.
#     Taking 'pwms' as an example, the final -s is stripped from the property
#     name, and #pwm-cells is looked up in the node for the controller
#     (&ctrl-1/&ctrl-2) to determine the number of data values after the
#     phandle. The binding for each controller must also have a *-cells key
#     (e.g. pwm-cells), giving names to data values. See below for an
#     explanation of *-cells.
#
#     A *-names (e.g. pwm-names) property can appear on the node as well,
#     giving a name to each entry (the 'pwms' example above has two entries,
#     <&ctrl-1 1 2> and <&ctrl-2 3 4>).
#
#     Because other property names are derived from the name of the property by
#     removing the final -s, the property name must end in -s. An error is
#     raised if it doesn't.
#
#     *-gpios properties are special-cased so that e.g. foo-gpios resolves to
#     #gpio-cells rather than #foo-gpio-cells.
#
#     All phandle-array properties support mapping through *-map properties,
#     e.g. gpio-map. See the devicetree spec.
#
#   - 'type: path' is for properties that are assigned a path. Usually, this
#     would be done with a path reference:
#
#         foo = &label;
#
#     Plain strings are accepted too, and are verified to be a path to an
#     existing node:
#
#         foo = "/path/to/some/node";
#
#   - 'type: compound' is a catch-all for more complex types, e.g.
#
#         foo = <&label>, [01 02];
#
# 'type: array' and the other array types also allow splitting the value into
# several <> blocks, e.g. like this:
#
#     foo = <1 2>, <3 4>;                         // Okay for 'type: array'
#     foo = <&label1 &label2>, <&label3 &label4>; // Okay for 'type: phandles'
#     foo = <&label1 1 2>, <&label2 3 4>;         // Okay for 'type: phandle-array'
#     etc.
#
# A property with 'deprecated: True' indicates to both the user and the tooling
# that the property is meant to be phased out.  The tooling will report a
# warning if the devicetree includes the property that is flagged as deprecated.
# There will be no other impact to having 'deprecated: True' set on the property.
#
# The optional 'default:' setting gives a value that will be used if the
# property is missing from the device tree node. If 'default: <default>' is
# given for a property <prop> and <prop> is missing, then the output will be as
# if '<prop> = <default>' had appeared (except YAML data types are used for the
# default value).
#
# Note that it only makes sense to combine 'default:' with 'required: false'.
# Combining it with 'required: true' will raise an error.
#
# There is a risk in using 'default:' when the value in the binding may be
# incorrect for a particular board or hardware configuration.  For example,
# defaulting the capacity of the connected power cell in a charging IC binding
# is likely to be incorrect.  For such properties it's better to make the
# property 'required: true', forcing the devicetree maintainer into an explicit
# and witting choice.
#
# Driver developers should use their best judgment as to whether a value can be
# safely defaulted. Candidates for default values include delays that would
# different only under unusual conditions (such as intervening hardware), or
# configuration for devices that have a standard initial configuration (such as
# a USB audio headset).
#
# Properties may also be defaulted to the vendor-specified power-up default as
# long as they're independent. If changing one property would require changing
# another to create a consistent configuration then those properties should be
# made required.
#
# In any case where 'default:' is used the property documentation should
# explain why the value was selected and any conditions that would make it
# necessary to provide a different value.
#
# See below for examples of 'default:'. Putting 'default:' on any property type
# besides those used in the examples will raise an error.
properties:
    # Describes a property like 'current-speed = <115200>;'. We pretend that
    # it's obligatory for the example node and set 'required: true'.
    current-speed:
        type: int
        required: true
        description: Initial baud rate for bar-device

    # Describes an optional property like 'keys = "foo", "bar";'
    keys:
        type: string-array
        required: false
        description: Keys for bar-device

    # Describes an optional property like 'maximum-speed = "full-speed";
    # the enum specifies known values that the string property may take
    maximum-speed:
        type: string
        required: false
        description: Configures USB controllers to work up to a specific speed.
        enum:
           - "low-speed"
           - "full-speed"
           - "high-speed"
           - "super-speed"

    # Describes a required property '#address-cells = <1>';  the const
    # specifies that the value for the property is expected to be the value 1
    "#address-cells":
        type: int
        required: true
        const: 1

    int-with-default:
        type: int
        required: false
        default: 123
        description: Value for int register, default is power-up configuration.

    array-with-default:
        type: array
        required: false
        default: [1, 2, 3] # Same as 'array-with-default = <1 2 3>'

    string-with-default:
        type: string
        required: false
        default: "foo"

    string-array-with-default:
        type: string-array
        required: false
        default: ["foo", "bar"] # Same as 'string-array-with-default = "foo", "bar"'

    uint8-array-with-default:
        type: uint8-array
        required: false
        default: [0x12, 0x34] # Same as 'uint8-array-with-default = [12 34]'

# 'child-binding' can be used when a node has children that all share the same
# properties. Each child gets the contents of 'child-binding' as its binding
# (though an explicit 'compatible = ...' on the child node takes precedence, if
# a binding is found for it).
#
# The example below is for a binding for PWM LEDs, where the child nodes are
# required to have a 'pwms' property. It corresponds to this .dts structure
# (assuming the binding has 'compatible: "pwm-leds"'):
#
# pwmleds {
#         compatible = "pwm-leds";
#
#         red_pwm_led {
#                 pwms = <&pwm3 4 15625000>;
#         };
#         green_pwm_led {
#                 pwms = <&pwm3 0 15625000>;
#         };
#         ...
# };
child-binding:
    description: LED that uses PWM

    properties:
        pwms:
            type: phandle-array
            required: true

# 'child-binding' also works recursively. For example, the binding below would
# provide a binding for the 'grandchild' node in this .dts (assuming
# 'compatible: "foo"'):
#
# parent {
#         compatible = "foo";
#         child {
#                 grandchild {
#                         prop = <123>;
#                 };
#         };
# }
child-binding:
    description: ...

    ...

    child-binding:
        description: ...

        properties:
            prop:
                type: int
                required: true

# If the binding describes an interrupt controller, GPIO controller, pinmux
# device, or any other node referenced by other nodes via 'phandle-array'
# properties, then *-cells should be given.
#
# To understand the purpose of *-cells, assume that some node has
#
#     pwms = <&pwm-ctrl 1 2>;
#
# , where &pwm-ctrl refers to a node whose binding is this file.
#
# The <1 2> part of the property value is called a *specifier* (this
# terminology is from the devicetree specification), and contains additional
# data associated with the GPIO. Here, the specifier has two cells, and the
# node pointed at by &gpio-ctrl is expected to have '#pwm-cells = <2>'.
#
# *-cells gives a name to each cell in the specifier. These names are used when
# generating identifiers.
#
# In this example, assume that 1 refers to a pin and that 2 is a flag value.
# This gives a *-cells assignment like below.
pwm-cells:
    - channel # name of first cell
    - period  # name of second cell

# If the specifier is empty (e.g. '#clock-cells = <0>'), then *-cells can
# either be omitted (recommended) or set to an empty array. Note that an empty
# array is specified as e.g. 'clock-cells: []' in YAML.

# As a special case, all *-gpio properties map to the key 'gpio-cells',
# regardless of prefix
gpio-cells:
    - pin
    - flags