Subject: Re: [PATCH v3 1/7] dt-bindings: Arm: Add Firmware Framework for Armv8-A (FF-A) binding

From: Jens Wiklander <[email-masked]>
Date: Wed, 16 Dec 2020 14:46:59 +0100

On Wed, Dec 16, 2020 at 12:24:08PM +0000, Sudeep Holla wrote:
> On Mon, Dec 14, 2020 at 04:01:07PM -0600, Rob Herring wrote:
> > On Fri, Dec 04, 2020 at 12:11:31PM +0000, Sudeep Holla wrote:
> > > Since the FF-A v1.0 specification doesn't list the UUID of all the
> > > partitions in the discovery API, we need to specify the UUID of the
> > > partitions that need to be accessed by drivers within the kernel.
> > > 
> > > This binding to provide the list of partitions that kernel drivers
> > > may need to access.
> > > 
> > > Signed-off-by: Sudeep Holla <[email-masked]>
> > > ---
> > >  .../devicetree/bindings/arm/arm,ffa.yaml      | 58 +++++++++++++++++++
> > >  1 file changed, 58 insertions(+)
> > >  create mode 100644 Documentation/devicetree/bindings/arm/arm,ffa.yaml
> > > 
> > > diff --git a/Documentation/devicetree/bindings/arm/arm,ffa.yaml b/Documentation/devicetree/bindings/arm/arm,ffa.yaml
> > > new file mode 100644
> > > index 000000000000..a014a5801c34
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/arm/arm,ffa.yaml
> > > @@ -0,0 +1,58 @@
> > > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > > +%YAML 1.2
> > > +---
> > > +$id: http://devicetree.org/schemas/arm/arm,ffa.yaml#
> > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > +
> > > +title: Arm Firmware Framework for Arm v8-A (in-kernel users)
> > > +
> > > +maintainers:
> > > +  - Sudeep Holla <[email-masked]>
> > > +
> > > +description: |
> > > +  Firmware frameworks implementing partition according to the FF-A
> > > +  specification defined by ARM document number ARM DEN 0077A ("Arm Firmware
> > > +  Framework for Arm v8-A") [0], providing services to be used by other
> > > +  partitions.
> > > +
> > > +  [0] https://developer.arm.com/docs/den0077/latest
> > > +
> > > +properties:
> > > +  $nodename:
> > > +    const: ffa
> > > +
> > > +  compatible:
> > > +    oneOf:
> > > +      - const: arm,ffa-1.0
> > > +
> > > +patternProperties:
> > > +  "^ffa_partition[0-9]+$":
> > > +    type: object
> > > +    description: One or more child nodes, each describing an FFA partition.
> > > +    properties:
> > > +      $nodename:
> > > +        const: ffa_partition
> > > +
> > > +      compatible:
> > > +        oneOf:
> > > +          - const: arm,ffa-1.0-partition
> > > +
> > > +      uuid:
> > > +        $ref: '/schemas/types.yaml#definitions/string'
> > > +        description: |
> > > +          The 128-bit UUID [2] of the service implemented by this partition.
> > > +
> > > +          [2] https://tools.ietf.org/html/rfc4122
> > 
> > UUIDs are actually a known thing in json-schema with 'format: uuid'. 
> > The meta-schema will probably reject that, so we'll need to add support 
> > to dtschema. Maybe it should be a new definition to reference.
> >
> 
> Ah OK, I will try that and ask for help if I am stuck as I am still trying
> to learn these, not there yet 😄 
> 
> > > +
> > > +additionalProperties: false
> > > +
> > > +examples:
> > > +  - |
> > > +    ffa {
> > > +      compatible = "arm,ffa-1.0";
> > > +
> > > +      ffa_partition0 {
> > > +        compatible = "arm,ffa-1.0-partition";
> > > +        uuid = "12345678-9abc-def0-1234-56789abcdef0";
> > > +      };
> > > +    };
> >
> > This could all be simplified down to just a single property:
> >
> 
> Thanks for the suggestion, I would love this to force spec authors to
> stop relying on DT and add whatever needed in future to the spec as part
> of discovery APIs.
> 
> > arm,ffa-partitions = "12345678-9abc-def0-1234-56789abcdef0", 
> > 	"12345678-9abc-def0-1234-56789abcdef1"
> > 	"12345678-9abc-def0-1234-56789abcdef2";
> >
> > Obviously, that's not extensible, but do we need it to be?
> >
> 
> I prefer if we don't, but I will run this through spec authors so that
> they are aware of what we will do in DT which means they *have* to
> incorporate any future needs into the spec discovery apis.

Speaking of discovery apis, doesn't the FF-A spec already have that?
Or am I missing something?

Cheers,
Jens

> 
> Ah I forgot the spec author is cc-ed. @Achin please shout if you see
> issues with this approach.
> 
> --
> Regards,
> Sudeep

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