Re: Next steps for schema language

[Rob Herring <robh-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>]

On Fri, Nov 3, 2017 at 9:11 AM, Pantelis Antoniou
<pantelis.antoniou-OWPKS81ov/FWk0Htik3J/w@public.gmane.org> wrote:
> Hi Rob,
>
>> On Nov 3, 2017, at 15:59 , Rob Herring <robh-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> wrote:
>>
>> On Thu, Nov 2, 2017 at 11:44 AM, Grant Likely <grant.likely-s3s/WqlpOiPyB63q8FvJNQ@public.gmane.org> wrote:
>>> Hi Pantelis and Rob,
>>>
>>> After the workshop next week, I'm trying to capture the direction
>>> we're going for the schema format. Roughly I think we're aiming
>>> towards:
>>>
>>> - Schema files to be written in YAML
>>> - DT files shall remain written in DTS for the foreseeable future.
>>> YAML will be treated as an intermediary format
>>>  - That said, we'll try to make design decisions that allow YAML to
>>> be used as a source format.
>>> - All schema files and yaml-encoded-dt files must be parsable by stock
>>> YAML parsers
>>> - Schema files to use the jsonschema vocabulary
>>>  - (jsonschema assumes json files, but YAML is a superset so this will be okay)
>>>  - Extended to add vocabulary for DT concepts (ignored by stock validators)
>>>    - C-like expressions as used in Pantelis' yamldt could be added in this way
>>>  - Need to write a jsonschema "metaschema" do define DT specific extensions
>>>    - metaschema will be used to validate format of schema files
>>>    - Existing tools can confirm is schema files are in the right format.
>>>    - will make review a lot easier.
>>
>> I want to start small here with defining top-level board/soc bindings.
>> This is essentially just defining the root node compatible strings.
>> Seems easy enough, right? However, I quickly run into the problem of
>> how to match for when to apply the schema. "compatible" is the obvious
>> choice, but that's also what I'm checking. We can't key off of what we
>> are validating. So we really need 2 schema. The first is for matching
>> on any valid compatible for board, then 2nd is checking for valid
>> combinations (e.g. 1 board compatible followed by 1 SoC compatible). I
>> don't like that as we'd be listing compatibles twice. An alternative
>> would be we apply every board schema and exactly 1 must pass. Perhaps
>> we generate a schema that's a "oneOf" of all the boards? Then we just
>> need to tag board schemas in some way.
>>
>
> I’ve run into this as the first problem with validation using compatible properties.
>
> The way I’ve solved it is by having a ‘selected’ property that is generating
> a test for when to check a binding against a node.

Okay, but what's the "jsonschema way" to do this is my question really.

Your example is a bit different too. It's a generic match (has
compatible), then check something else (status). I have a binding
specific match and then a binding specific check on the same thing. We
could have the same thing for a device. Match on a set of compatibles
for a device, then check combination of compatibles along with other
properties. If you have '"example,soc2-uart",
"example,fallback-uart"', we need to match on either string, but check
that both strings are present because either one alone is not valid.
Then to add to that, you may have soc3, soc4, etc.

Rob