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

From: Sudeep Holla <sudeep.holla@arm.com>
To: Rob Herring <robh@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org,
	Trilok Soni <tsoni@codeaurora.org>,
	arve@android.com, Andrew Walbran <qwandor@google.com>,
	David Hartley <dhh@qti.qualcomm.com>,
	Achin Gupta <Achin.Gupta@arm.com>,
	Sudeep Holla <sudeep.holla@arm.com>,
	Jens Wiklander <jens.wiklander@linaro.org>,
	Arunachalam Ganapathy <arunachalam.ganapathy@arm.com>
Subject: Re: [PATCH v3 1/7] dt-bindings: Arm: Add Firmware Framework for Armv8-A (FF-A) binding
Date: Wed, 16 Dec 2020 12:24:08 +0000	[thread overview]
Message-ID: <20201216122408.2fhubdyqm2ofpgc3@bogus> (raw)
In-Reply-To: <20201214220107.GA2430387@robh.at.kernel.org>

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 <sudeep.holla@arm.com>
> > ---
> >  .../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 <sudeep.holla@arm.com>
> > +
> > +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.

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

--
Regards,
Sudeep