linux-kernel - RE: [PATCH v6 1/3] dt-bindings: add device tree binding for Arm CryptoCell trng engine

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Message-ID: <DB6PR0802MB25334E308B8D4B10D2562460E9CF0@DB6PR0802MB2533.eurprd08.prod.outlook.com>
Date:   Thu, 26 Mar 2020 21:04:46 +0000
From:   Hadar Gat <Hadar.Gat@....com>
To:     Rob Herring <robh@...nel.org>
CC:     Matt Mackall <mpm@...enic.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Mark Rutland <Mark.Rutland@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Alexander Sverdlin <alexander.sverdlin@...ia.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tomer Maimon <tmaimon77@...il.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Zaibo Xu <xuzaibo@...wei.com>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Gilad Ben-Yossef <gilad@...yossef.com>,
        Ofir Drang <Ofir.Drang@....com>, nd <nd@....com>
Subject: RE: [PATCH v6 1/3] dt-bindings: add device tree binding for Arm
 CryptoCell trng engine

Hi Rob,

> 
> On Wed, Mar 25, 2020 at 07:41:09AM +0200, Hadar Gat wrote:
> > The Arm CryptoCell is a hardware security engine. This patch adds DT
> > bindings for its TRNG (True Random Number Generator) engine.
> >
> > Signed-off-by: Hadar Gat <hadar.gat@....com>
> > ---
> >  .../devicetree/bindings/rng/arm-cctrng.yaml        | 55
> ++++++++++++++++++++++
> >  1 file changed, 55 insertions(+)
> >  create mode 100644
> > Documentation/devicetree/bindings/rng/arm-cctrng.yaml
> >
> > diff --git a/Documentation/devicetree/bindings/rng/arm-cctrng.yaml
> > b/Documentation/devicetree/bindings/rng/arm-cctrng.yaml
> > new file mode 100644
> > index 0000000..7f70e4b
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/rng/arm-cctrng.yaml
> > @@ -0,0 +1,55 @@
> > +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause) %YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/rng/arm-cctrng.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Arm TrustZone CryptoCell TRNG engine
> > +
> > +maintainers:
> > +  - Hadar Gat <hadar.gat@....com>
> > +
> > +description: |+
> > +  Arm TrustZone CryptoCell TRNG (True Random Number Generator)
> engine.
> > +
> > +properties:
> > +  compatible:
> > +    enum:
> > +      - arm,cryptocell-713-trng
> > +      - arm,cryptocell-703-trng
> > +
> > +  interrupts:
> > +    maxItems: 1
> > +
> > +  reg:
> > +    maxItems: 1
> > +
> > +  arm,rosc-ratio:
> > +    description:
> > +      Arm TrustZone CryptoCell TRNG engine has 4 ring oscillators.
> > +      Sampling ratio values for these 4 ring oscillators. (from calibration)
> > +    allOf:
> > +      - $ref: /schemas/types.yaml#/definitions/uint32-array
> > +      - items:
> > +          minItems: 4
> > +          maxItems: 4
> 
> Aren't there some constraints on the values?
> 
> If not, then just this is enough:
> 
> - maxItems: 4
> 
The constraint is just on the array size and not on the values.
The array is of 4 elements for the CryptoCell 4 ring oscillators.
Isn't 'minitems:' is about the array min size? Isn't it the way to block less than 4 items? This is what I want to do.
I'm a bit confused if it is required or not..

> > +
> > +  clocks:
> > +    maxItems: 1
> > +
> > +required:
> > +  - compatible
> > +  - interrupts
> > +  - reg
> > +  - arm,rosc-ratio
> > +
> > +additionalProperties: false
> > +
> > +examples:
> > +  - |
> > +    arm_cctrng: rng@...00000 {
> > +        compatible = "arm,cryptocell-713-trng";
> > +        interrupts = <0 29 4>;
> > +        reg = <0x60000000 0x10000>;
> > +        arm,rosc-ratio = <5000 1000 500 0>;
> > +    };
> > --
> > 2.7.4
> >

Thanks,
Hadar