Documentation/devicetree/bindings/writing-bindings.rst

   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   See property-units.txt.
  56
  57 - DO define properties in terms of constraints. How many entries? What are
  58   possible values? What is the order?
  59
  60
  61 Board/SoC .dts Files
  62 ====================
  63
  64 - DO put all MMIO devices under a bus node and not at the top-level.
  65
  66 - DO use non-empty 'ranges' to limit the size of child buses/devices. 64-bit
  67   platforms don't need all devices to have 64-bit address and size.