linux-kernel - Re: [RFC PATCH] dt-bindings: add a jsonschema binding example

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Message-ID: <152426770474.46528.1592920281091105196@swboyd.mtv.corp.google.com>
Date:   Fri, 20 Apr 2018 16:41:44 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     Rob Herring <robh@...nel.org>
Cc:     devicetree-spec@...r.kernel.org, devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Grant Likely <grant.likely@....com>,
        Frank Rowand <frowand.list@...il.com>,
        Mark Rutland <mark.rutland@....com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Linus Walleij <linus.walleij@...aro.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Jonathan Cameron <jic23@...nel.org>
Subject: Re: [RFC PATCH] dt-bindings: add a jsonschema binding example

Quoting Rob Herring (2018-04-20 11:15:04)
> On Fri, Apr 20, 2018 at 11:47 AM, Stephen Boyd <sboyd@...nel.org> wrote:
> > Quoting Rob Herring (2018-04-18 15:29:05)
> >> diff --git a/Documentation/devicetree/bindings/example-schema.yaml b/Documentation/devicetree/bindings/example-schema.yaml
> >> new file mode 100644
> >> index 000000000000..fe0a3bd1668e
> >> --- /dev/null
> >> +++ b/Documentation/devicetree/bindings/example-schema.yaml
> >> @@ -0,0 +1,149 @@
> >> +
> >> +  The end of the description is marked by indentation less than the first line
> >> +  in the description.
> >> +
> >> +select: false
> >> +  # 'select' is a schema applied to a DT node to determine if this binding
> >> +  # schema should be applied to the node. It is optional and by default the
> >> +  # possible compatible strings are extracted and used to match.
> >
> > Can we get a concrete example here?
> 
> select: true
> 
> :) Which is apply to every node.
> 
> A better one is from the memory node schema ('$nodename' gets added :
> 
> select:
>   required: ["$nodename"]
>   properties:
>     $nodename:
>       oneOf:
>         - pattern: "^memory@[0-9a-f]*"
>         - const: "memory" # 'memory' only allowed for selecting
> 
> 
> I expect the vast majority of device bindings will not use select at
> all and rely on compatible string matching.

Thanks! I was looking to see how the select syntax would work and this
shows one example nicely. I suppose another way would be to show how a
compatible string would be matched through select, even though it's
redundant.

Is there a way we can enforce node names through the schema too? For
example to enforce that a clock controller is called 'clock-controller'
or a spi master is called 'spi'.

> 
> >> +
> >> +properties:
> > [...]
> >> +
> >> +  interrupts:
> >> +    # Either 1 or 2 interrupts can be present
> >> +    minItems: 1
> >> +    maxItems: 2
> >> +    items:
> >> +      - description: tx or combined interrupt
> >> +      - description: rx interrupt
> >> +
> >> +    description: |
> >
> > The '|' is needed to make yaml happy?
> 
> Yes, this is simply how you do literal text blocks in yaml.
> 
> We don't really need for this one really, but for the top-level
> 'description' we do. The long term intent is 'description' would be
> written in sphinx/rst and can be extracted into the DT spec (for
> common bindings). Grant has experimented with that some.

Ok. That sounds cool. Then we could embed links to datasheets and SVGs
too.

> 
> >> +      A variable number of interrupts warrants a description of what conditions
> >> +      affect the number of interrupts. Otherwise, descriptions on standard
> >> +      properties are not necessary.
> >> +
> >> +  interrupt-names:
> >> +    # minItems must be specified here because the default would be 2
> >> +    minItems: 1
> >> +    items:
> >> +      - const: "tx irq"
> >> +      - const: "rx irq"
> >> +
> >> +  # Property names starting with '#' must be quoted
> >> +  '#interrupt-cells':
> >> +    # A simple case where the value must always be '2'.
> >> +    # The core schema handles that this must be a single integer.
> >> +    const: 2
> >> +
> >> +  interrupt-controller: {}
> >
> > Does '{}' mean nothing to see here?
> 
> Yes. It's just an empty schema that's always valid.

Could we include another schema to indicate that this is an interrupt
controller? I'm sort of asking for multi-schema inheritance.

> 
> >> +  foo-gpios:
> >> +    maxItems: 1
> >> +    description: A connection of the 'foo' gpio line.
> >> +
> >> +  vendor,int-property:
> >> +    description: Vendor specific properties must have a description
> >> +    type: integer # A type is also required
> >> +    enum: [2, 4, 6, 8, 10]
> >> +
> >> +  vendor,bool-property:
> >> +    description: Vendor specific properties must have a description
> >> +    type: boolean
> >> +
> >> +required:
> >> +  - compatible
> >> +  - reg
> >> +  - interrupts
> >> +  - interrupt-controller
> >
> > Can the required or optional parts go under each property instead of
> > having a different section?
> 
> No, because then it is not json-schema language.
> 
> > Or does that make the schema parser
> > difficult to implement?
> 
> Yes, because then we have to implement a schema parser.

:/