1.. SPDX-License-Identifier: GPL-2.0
2
3============================================================
4DOs and DON'Ts for designing and writing Devicetree bindings
5============================================================
6
7This is a list of common review feedback items focused on binding design. With
8every rule, there are exceptions and bindings have many gray areas.
9
10For guidelines related to patches, see
11Documentation/devicetree/bindings/submitting-patches.rst
12
13
14Overall design
15==============
16
17- DO attempt to make bindings complete even if a driver doesn't support some
18  features. For example, if a device has an interrupt, then include the
19  'interrupts' property even if the driver is only polled mode.
20
21- DON'T refer to Linux or "device driver" in bindings. Bindings should be
22  based on what the hardware has, not what an OS and driver currently support.
23
24- DO use node names matching the class of the device. Many standard names are
25  defined in the DT Spec. If there isn't one, consider adding it.
26
27- DO check that the example matches the documentation especially after making
28  review changes.
29
30- DON'T create nodes just for the sake of instantiating drivers. Multi-function
31  devices only need child nodes when the child nodes have their own DT
32  resources. A single node can be multiple providers (e.g. clocks and resets).
33
34- DON'T use 'syscon' alone without a specific compatible string. A 'syscon'
35  hardware block should have a compatible string unique enough to infer the
36  register layout of the entire block (at a minimum).
37
38
39Properties
40==========
41
42- DO make 'compatible' properties specific. DON'T use wildcards in compatible
43  strings. DO use fallback compatibles when devices are the same as or a subset
44  of prior implementations. DO add new compatibles in case there are new
45  features or bugs.
46
47- DO use a vendor prefix on device-specific property names. Consider if
48  properties could be common among devices of the same class. Check other
49  existing bindings for similar devices.
50
51- DON'T redefine common properties. Just reference the definition and define
52  constraints specific to the device.
53
54- DO use common property unit suffixes for properties with scientific units.
55  Recommended suffixes are listed at
56  https://github.com/devicetree-org/dt-schema/blob/master/schemas/property-units.yaml
57
58- DO define properties in terms of constraints. How many entries? What are
59  possible values? What is the order?
60
61Typical cases and caveats
62=========================
63
64- Phandle entries, like clocks/dmas/interrupts/resets, should always be
65  explicitly ordered. Include the {clock,dma,interrupt,reset}-names if there is
66  more than one phandle. When used, both of these fields need the same
67  constraints (e.g.  list of items).
68
69- For names used in {clock,dma,interrupt,reset}-names, do not add any suffix,
70  e.g.: "tx" instead of "txirq" (for interrupt).
71
72- Properties without schema types (e.g. without standard suffix or not defined
73  by schema) need the type, even if this is an enum.
74
75- If schema includes other schema (e.g. /schemas/i2c/i2c-controller.yaml) use
76  "unevaluatedProperties:false". In other cases, usually use
77  "additionalProperties:false".
78
79- For sub-blocks/components of bigger device (e.g. SoC blocks) use rather
80  device-based compatible (e.g. SoC-based compatible), instead of custom
81  versioning of that component.
82  For example use "vendor,soc1234-i2c" instead of "vendor,i2c-v2".
83
84- "syscon" is not a generic property. Use vendor and type, e.g.
85  "vendor,power-manager-syscon".
86
87Board/SoC .dts Files
88====================
89
90- DO put all MMIO devices under a bus node and not at the top-level.
91
92- DO use non-empty 'ranges' to limit the size of child buses/devices. 64-bit
93  platforms don't need all devices to have 64-bit address and size.
94