FreeBSD/Linux Kernel Cross Reference
sys/contrib/device-tree/Bindings/writing-bindings.rst

     .. SPDX-License-Identifier: GPL-2.0
     
     ============================================================
     DOs and DON'Ts for designing and writing Devicetree bindings
     ============================================================
     
     This is a list of common review feedback items focused on binding design. With
     every rule, there are exceptions and bindings have many gray areas.
     
    For guidelines related to patches, see
    Documentation/devicetree/bindings/submitting-patches.rst
    
    
    Overall design
    ==============
    
    - DO attempt to make bindings complete even if a driver doesn't support some
      features. For example, if a device has an interrupt, then include the
      'interrupts' property even if the driver is only polled mode.
    
    - DON'T refer to Linux or "device driver" in bindings. Bindings should be
      based on what the hardware has, not what an OS and driver currently support.
    
    - DO use node names matching the class of the device. Many standard names are
      defined in the DT Spec. If there isn't one, consider adding it.
    
    - DO check that the example matches the documentation especially after making
      review changes.
    
    - DON'T create nodes just for the sake of instantiating drivers. Multi-function
      devices only need child nodes when the child nodes have their own DT
      resources. A single node can be multiple providers (e.g. clocks and resets).
    
    - DON'T use 'syscon' alone without a specific compatible string. A 'syscon'
      hardware block should have a compatible string unique enough to infer the
      register layout of the entire block (at a minimum).
    
    
    Properties
    ==========
    
    - DO make 'compatible' properties specific. DON'T use wildcards in compatible
      strings. DO use fallback compatibles when devices are the same as or a subset
      of prior implementations. DO add new compatibles in case there are new
      features or bugs.
    
    - DO use a vendor prefix on device-specific property names. Consider if
      properties could be common among devices of the same class. Check other
      existing bindings for similar devices.
    
    - DON'T redefine common properties. Just reference the definition and define
      constraints specific to the device.
    
    - DO use common property unit suffixes for properties with scientific units.
      Recommended suffixes are listed at
      https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/property-units.yaml
    
    - DO define properties in terms of constraints. How many entries? What are
      possible values? What is the order?
    
    Typical cases and caveats
    =========================
    
    - Phandle entries, like clocks/dmas/interrupts/resets, should always be
      explicitly ordered. Include the {clock,dma,interrupt,reset}-names if there is
      more than one phandle. When used, both of these fields need the same
      constraints (e.g.  list of items).
    
    - For names used in {clock,dma,interrupt,reset}-names, do not add any suffix,
      e.g.: "tx" instead of "txirq" (for interrupt).
    
    - Properties without schema types (e.g. without standard suffix or not defined
      by schema) need the type, even if this is an enum.
    
    - If schema includes other schema (e.g. /schemas/i2c/i2c-controller.yaml) use
      "unevaluatedProperties:false". In other cases, usually use
      "additionalProperties:false".
    
    - For sub-blocks/components of bigger device (e.g. SoC blocks) use rather
      device-based compatible (e.g. SoC-based compatible), instead of custom
      versioning of that component.
      For example use "vendor,soc1234-i2c" instead of "vendor,i2c-v2".
    
    - "syscon" is not a generic property. Use vendor and type, e.g.
      "vendor,power-manager-syscon".
    
    Board/SoC .dts Files
    ====================
    
    - DO put all MMIO devices under a bus node and not at the top-level.
    
    - DO use non-empty 'ranges' to limit the size of child buses/devices. 64-bit
      platforms don't need all devices to have 64-bit address and size.

Cache object: cc1dabc576353e67e462ccc0ce520cd4