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Diffstat (limited to 'Documentation/devicetree/bindings/writing-schema.rst')
| -rw-r--r-- | Documentation/devicetree/bindings/writing-schema.rst | 81 |
1 files changed, 76 insertions, 5 deletions
diff --git a/Documentation/devicetree/bindings/writing-schema.rst b/Documentation/devicetree/bindings/writing-schema.rst index 4a381d20f2b4..05c34248e544 100644 --- a/Documentation/devicetree/bindings/writing-schema.rst +++ b/Documentation/devicetree/bindings/writing-schema.rst @@ -31,7 +31,7 @@ $schema Indicates the meta-schema the schema file adheres to. title - A one-line description on the contents of the binding schema. + A one-line description of the hardware being described in the binding schema. maintainers A DT specific property. Contains a list of email address(es) @@ -39,10 +39,40 @@ maintainers description Optional. A multi-line text block containing any detailed - information about this binding. It should contain things such as what the block + information about this hardware. It should contain things such as what the block or device does, standards the device conforms to, and links to datasheets for more information. + The YAML format has several options for defining the formatting of the text + block. The options are controlled with indicator characters following the key + (e.g. "description: \|"). The minimum formatting needed for a block should be + used. The formatting controls can not only affect whether the YAML can be + parsed correctly, but are important when the text blocks are rendered to + another form. The options are as follows. + + The default without any indicators is flowed, plain scalar style where single + line breaks and leading whitespace are stripped. Paragraphs are delimited by + blank lines (i.e. double line break). This style cannot contain ": " in it as + it will be interpreted as a key. Any " #" sequence will be interpreted as + a comment. There's other restrictions on characters as well. Most + restrictions are on what the first character can be. + + The second style is folded which is indicated by ">" character. In addition + to maintaining line breaks on double line breaks, the folded style also + maintains leading whitespace beyond indentation of the first line. The line + breaks on indented lines are also maintained. + + The third style is literal which is indicated by "\|" character. The literal + style maintains all line breaks and whitespace (beyond indentation of the + first line). + + The above is not a complete description of YAML text blocks. More details on + multi-line YAML text blocks can be found online: + + https://yaml-multiline.info/ + + https://www.yaml.info/learn/quote.html + select Optional. A json-schema used to match nodes for applying the schema. By default, without 'select', nodes are matched against their possible @@ -71,9 +101,36 @@ required A list of DT properties from the 'properties' section that must always be present. +additionalProperties / unevaluatedProperties + Keywords controlling how schema will validate properties not matched by this + schema's 'properties' or 'patternProperties'. Each schema is supposed to + have exactly one of these keywords in top-level part, so either + additionalProperties or unevaluatedProperties. Nested nodes, so properties + being objects, are supposed to have one as well. + + * additionalProperties: false + Most common case, where no additional schema is referenced or if this + binding allows subset of properties from other referenced schemas. + + * unevaluatedProperties: false + Used when this binding references other schema whose all properties + should be allowed. + + * additionalProperties: true + - Top-level part: + Rare case, used for schemas implementing common set of properties. Such + schemas are supposed to be referenced by other schemas, which then use + 'unevaluatedProperties: false'. Typically bus or common-part schemas. + - Nested node: + When listing only the expected compatible of the nested node and there + is an another schema matching that compatible which ends with one of + two above cases ('false'). + examples - Optional. A list of one or more DTS hunks implementing the - binding. Note: YAML doesn't allow leading tabs, so spaces must be used instead. + Optional. A list of one or more DTS hunks implementing this binding only. + Example should not contain unrelated device nodes, e.g. consumer nodes in a + provider binding, other nodes referenced by phandle. + Note: YAML doesn't allow leading tabs, so spaces must be used instead. Unless noted otherwise, all properties are required. @@ -108,12 +165,23 @@ The YAML Devicetree format also makes all string values an array and scalar values a matrix (in order to define groupings) even when only a single value is present. Single entries in schemas are fixed up to match this encoding. +When bindings cover multiple similar devices that differ in some properties, +those properties should be constrained for each device. This usually means: + + * In top level 'properties' define the property with the broadest constraints. + * In 'if:then:' blocks, further narrow the constraints for those properties. + * Do not define the properties within an 'if:then:' block (note that + 'additionalItems' also won't allow that). + Coding style ------------ Use YAML coding style (two-space indentation). For DTS examples in the schema, preferred is four-space indentation. +Place entries in 'properties' and 'required' sections in the same order, using +style from Documentation/devicetree/bindings/dts-coding-style.rst. + Testing ------- @@ -159,11 +227,14 @@ It is possible to run both in a single command:: make dt_binding_check dtbs_check It is also possible to run checks with a subset of matching schema files by -setting the ``DT_SCHEMA_FILES`` variable to a specific schema file or pattern. +setting the ``DT_SCHEMA_FILES`` variable to 1 or more specific schema files or +patterns (partial match of a fixed string). Each file or pattern should be +separated by ':'. :: make dt_binding_check DT_SCHEMA_FILES=trivial-devices.yaml + make dt_binding_check DT_SCHEMA_FILES=trivial-devices.yaml:rtc.yaml make dt_binding_check DT_SCHEMA_FILES=/gpio/ make dtbs_check DT_SCHEMA_FILES=trivial-devices.yaml |