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Diffstat (limited to 'Documentation/devicetree/bindings/writing-bindings.rst')
| -rw-r--r-- | Documentation/devicetree/bindings/writing-bindings.rst | 51 |
1 files changed, 45 insertions, 6 deletions
diff --git a/Documentation/devicetree/bindings/writing-bindings.rst b/Documentation/devicetree/bindings/writing-bindings.rst index 1ad081de2dd0..667816dd7d50 100644 --- a/Documentation/devicetree/bindings/writing-bindings.rst +++ b/Documentation/devicetree/bindings/writing-bindings.rst @@ -31,18 +31,39 @@ Overall design 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 treat device node names as a stable ABI, but instead use phandles or + compatibles to find sibling devices. Exception: sub-nodes of given device + could be treated as ABI, if explicitly documented in the bindings. + - 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). +- DON'T use 'simple-mfd' compatible for non-trivial devices, where children + depend on some resources from the parent. Similarly, 'simple-bus' should not + be used for complex buses and even 'regs' property means device is not + a simple bus. + 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 make 'compatible' properties specific. + + - DON'T use wildcards or device-family names in compatible strings. + + - DO use fallback compatibles when devices are the same as or a superset of + prior implementations. + + - DO add new compatibles in case there are new features or bugs. + + - DO use a SoC-specific compatible for all SoC devices, followed by a + fallback if appropriate. SoC-specific compatibles are also preferred for + the fallbacks. + + - DON'T use bus suffixes to encode the type of interface device is using. + The parent bus node already implies that interface. DON'T add the type of + device, if the device cannot be anything else. - DO use a vendor prefix on device-specific property names. Consider if properties could be common among devices of the same class. Check other @@ -51,12 +72,21 @@ Properties - DON'T redefine common properties. Just reference the definition and define constraints specific to the device. +- DON'T add properties to avoid a specific compatible. DON'T add properties if + they are implied by (deducible from) the compatible. + - 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? + possible values? What is the order? All these constraints represent the ABI + as well. + +- DON'T make changes that break the ABI without explicit and detailed rationale + for why the changes have to be made and their impact. ABI impact goes beyond + the Linux kernel, because it also covers other open-source upstream projects. + Typical cases and caveats ========================= @@ -64,7 +94,7 @@ 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). + 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). @@ -84,6 +114,15 @@ Typical cases and caveats - "syscon" is not a generic property. Use vendor and type, e.g. "vendor,power-manager-syscon". +- Do not add instance index (IDs) properties or custom OF aliases. If the + devices have different programming model, they might need different + compatibles. If such devices use some other device in a different way, e.g. + they program the phy differently, use cell/phandle arguments. + +- Bindings files should be named like compatible: vendor,device.yaml. In case + of multiple compatibles in the binding, use one of the fallbacks or a more + generic name, yet still matching compatible style. + Board/SoC .dts Files ==================== |