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

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Date:   Thu, 13 Feb 2020 10:21:37 +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

Thanks Rob for your clarifications. I surly learned more about .yaml schema.
All fixes will be applied in the next patch version (v4).
Hadar

> On Sun, Feb 9, 2020 at 3:34 AM Hadar Gat <Hadar.Gat@....com> wrote:
> >
> > 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?
> 
> Maybe not now, but both will always have the same errata and features?
> 2 is not a large number, so just do 2.
> 
> Of course, errata can vary by revision. Most Arm IP has version registers, so I
> assume that's true here. If not, we'd need per SoC implementation
> compatible strings here.
> 
> > (checking out other rng drivers, I see this example in
> Samsung,exynos4.yaml:
> >   - samsung,exynos4-rng # for Exynos4210 and Exynos4412 )
> 
> Well, there's lots of bad examples, and also, some Samsung bindings are
> declared to not be stable.
> 
> >
> > > > +
> > > > +  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)
> 
> Don't need a description as that's constraints the schema should express.
> 
> > > 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"?
> 
> arm,rosc-ratio:
>   allOf:
>     - $ref: /schemas/types.yaml#/definitions/uint32-array
>   maxItems: 4
> 
> > 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)
> 
> No, the property name is always 'clocks'. You need just 'maxItems: 1'
> if there's a single clock.
> 
> Rob