1 .. SPDX-License-Identifier: GPL-2.0
2
3 ============================================================
4 DOs and DON'Ts for designing and writing Devicetree bindings
5 ============================================================
6
7 This is a list of common review feedback items focused on binding design. With
8 every rule, there are exceptions and bindings have many gray areas.
9
10 For guidelines related to patches, see
11 Documentation/devicetree/bindings/submitting-patches.rst
12
13
14 Overall 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
39 Properties
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/main/dtschema/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
61 Typical 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
87 Board/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.
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