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

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Date:   Thu, 26 Mar 2020 13:41:04 -0600
From:   Rob Herring <robh@...nel.org>
To:     Hadar Gat <hadar.gat@....com>
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, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Gilad Ben-Yossef <gilad@...yossef.com>,
        Ofir Drang <ofir.drang@....com>
Subject: Re: [PATCH v6 1/3] dt-bindings: add device tree binding for Arm
 CryptoCell trng engine

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

> +
> +  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
>