linux-kernel - RE: [PATCH v2 1/3] dt-bindings: add device tree binding for Arm CryptoCell trng engine

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Date:   Sun, 9 Feb 2020 09:33:44 +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>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Tomer Maimon <tmaimon77@...il.com>,
        Stefan Wahren <wahrenst@....net>,
        Sumit Garg <sumit.garg@...aro.org>,
        Zaibo Xu <xuzaibo@...wei.com>,
        Weili Qian <qianweili@...wei.com>,
        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 v2 1/3] dt-bindings: add device tree binding for Arm
 CryptoCell trng engine

Hi Rob,
Thanks for remarks.
Please see my answers.
Hadar

> On Sun, Feb 02, 2020 at 03:26:59PM +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        | 51
> ++++++++++++++++++++++
> >  1 file changed, 51 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..fe9422e
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/rng/arm-cctrng.yaml
> > @@ -0,0 +1,51 @@
> > +# SPDX-License-Identifier: GPL-2.0
> 
> Dual license new bindings:
> 
> (GPL-2.0-only OR BSD-2-Clause)
> 
Okay.

> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/rng/arm-cctrng.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Arm ZrustZone CryptoCell TRNG engine
> > +
> > +maintainers:
> > +  - Hadar Gat <hadar.gat@....com>
> > +
> > +description: |+
> > +  Arm ZrustZone CryptoCell TRNG (True Random Number Generator)
> engine.
> > +
> > +properties:
> > +  compatible:
> > +    description: Should be "arm,cryptocell-7x3-trng"
> 
> Drop. That's what the schema says.
> 
Okay.

> > +    const: arm,cryptocell-7x3-trng
> 
> Is 'x' a wildcard? We don't do wildcards unless you have other ways to get the
> specific version.
> 
Kind of a wildcard. It stands for either 703 or 713.
Should I fix this to the specific versions?
OR,
Since the specific version doesn't matter to the driver, should it changed?
(checking out other rng drivers, I see this example in Samsung,exynos4.yaml:
  - samsung,exynos4-rng	# for Exynos4210 and Exynos4412 )

> > +
> > +  interrupts:
> > +    description: Interrupt number for the device.
> 
> Drop. That's all 'interrupts'.
> 
Okay.

> > +    maxItems: 1
> > +
> > +  reg:
> > +    description: Base physical address of the engine and length of memory
> > +                 mapped region.
> 
> Drop.
> 
Okay.

> > +    maxItems: 1
> > +
> > +  rosc-ratio:
> > +    description: Sampling ratio values from calibration for 4 ring oscillators.
> > +    maxItems: 1
> 
> Is this an array?
> 
Yes, array of 4. (I'll mention in the description)

> Needs a vendor prefix, a type ref and any constraints you can come up with.
> 
Do you mean in the name? instead of "rosc-ratio"?
I didn't find anything about it in the documentation or examples in other rng drivers..

> > +
> > +  clocks:
> > +    description: Reference to the crypto engine clock.
> 
> How many clocks?
> 
One clock. (I will change clocks --> clock)

> > +
> > +required:
> > +  - compatible
> > +  - interrupts
> > +  - reg
> > +  - rosc-ratio
> > +
> > +additionalProperties: false
> > +
> > +examples:
> > +  - |
> > +    arm_cctrng: arm_cctrng@...00000 {
> 
> rng@...
> 
Okay.

> > +        compatible = "arm,cryptocell-7x3-trng";
> > +        interrupts = <0 29 4>;
> > +        reg = <0x60000000 0x10000>;
> > +        rosc-ratio = <5000 1000 500 0>;
> > +    };
> > --
> > 2.7.4
> >