netdev - Re: [PATCH net-next 1/7] dt-bindings: net: sff,sfp: update binding

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Date:   Thu, 20 Oct 2022 17:06:12 -0500
From:   Rob Herring <robh@...nel.org>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        devicetree@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH net-next 1/7] dt-bindings: net: sff,sfp: update binding

On Thu, Oct 20, 2022 at 11:08 AM Russell King (Oracle)
<linux@...linux.org.uk> wrote:
>
> On Thu, Oct 20, 2022 at 09:27:44AM -0500, Rob Herring wrote:
> > On Thu, Oct 20, 2022 at 9:19 AM Rob Herring <robh@...nel.org> wrote:
> > >
> > > On Thu, Oct 20, 2022 at 09:28:25AM +0100, Russell King (Oracle) wrote:
> > > > On Wed, Oct 19, 2022 at 06:31:53PM -0500, Rob Herring wrote:
> > > > > On Wed, 19 Oct 2022 14:28:46 +0100, Russell King (Oracle) wrote:
> > > > > > Add a minimum and default for the maximum-power-milliwatt option;
> > > > > > module power levels were originally up to 1W, so this is the default
> > > > > > and the minimum power level we can have for a functional SFP cage.
> > > > > >
> > > > > > Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>
> > > > > > ---
> > > > > >  Documentation/devicetree/bindings/net/sff,sfp.yaml | 2 ++
> > > > > >  1 file changed, 2 insertions(+)
> > > > > >
> > > > >
> > > > > My bot found errors running 'make DT_CHECKER_FLAGS=-m dt_binding_check'
> > > > > on your patch (DT_CHECKER_FLAGS is new in v5.13):
> > > > >
> > > > > yamllint warnings/errors:
> > > > >
> > > > > dtschema/dtc warnings/errors:
> > > > > /builds/robherring/dt-review-ci/linux/Documentation/devicetree/bindings/net/sff,sfp.yaml: properties:maximum-power-milliwatt: 'minimum' should not be valid under {'enum': ['const', 'enum', 'exclusiveMaximum', 'exclusiveMinimum', 'minimum', 'maximum', 'multipleOf', 'pattern']}
> > > > >     hint: Scalar and array keywords cannot be mixed
> > > > >     from schema $id: http://devicetree.org/meta-schemas/keywords.yaml#
> > > >
> > > > I'm reading that error message and it means absolutely nothing to me.
> > > > Please can you explain it (and also re-word it to be clearer)?
> > >
> > > 'maxItems' is a constraint for arrays. 'maximum' is a constraint for
> > > scalar values. Mixing them does not make sense.
> >
> > TBC, dropping 'maxItems' is what is needed here.
>
> So how does this work?

Do you really want to know? ;)

>
> maxItems: 1

json-schema happily ignores any keywords that it doesn't understand or
don't make sense for a specific context. The DT meta-schema tries to
prevent that.

> tells it that there should be an array of one property, which is at the
> DT level fundamentally the same as a scalar property.

Yes, it is true that the YAML encoded DT and (currently) the internal
encoding used by the tools encode everything as matrices simply
because dtc doing the YAML encoding doesn't know the types beyond what
DTS source level provides, so everything has to be the same encoding.
Now we use the type information in the schemas to decode the DTBs
directly and don't have that limitation. Once I remove the YAML
encoding, we can stop encoding everything as a matrix and having to
fixup the schemas from scalar -> array -> matrix.

> minimum:
> default:
> maximum:
>
> tells it that this is a scalar property, so there should be exactly one
> item or the property should not be mentioned?

Not sure I follow the question. As the property is defined as a
scalar, it only needs scalar keywords. Internally, the schema gets
expanded to:

prop:
  minItems: 1
  maxItems: 1
  items:
    - maxItems: 1
      minItems: 1
      items:
        - maximum: ???
          minimum: ???
          default: ???

This is what processed-schemas.json will contain if you just have the
scalar keywords.

It's a bit more messy now with the unit suffixes as initially they
were all scalars, but over time we've had to allow for arrays. So it's
really they default to scalars unless you need an array in which you
can define:

prop:
  maxItems: 2
  items:
    maximum: ???

Could you do 'maxItems: 1' here? Yes, that would be a valid schema,
but IIRC we'll still complain because it is redundant.

Rob