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From:   Vabhav Sharma <vabhav.sharma@nxp.com>
To:     Rob Herring <robh@kernel.org>
CC:     Horia Geanta <horia.geanta@nxp.com>,
        Gaurav Jain <gaurav.jain@nxp.com>,
        Pankaj Gupta <pankaj.gupta@nxp.com>,
        "herbert@gondor.apana.org.au" <herbert@gondor.apana.org.au>,
        "davem@davemloft.net" <davem@davemloft.net>,
        "shawnguo@kernel.org" <shawnguo@kernel.org>,
        "linux-crypto@vger.kernel.org" <linux-crypto@vger.kernel.org>,
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        <linux-arm-kernel@lists.infradead.org>,
        Silvano Di Ninno <silvano.dininno@nxp.com>,
        Varun Sethi <V.Sethi@nxp.com>
Subject: RE: [EXT] Re: [PATCH 1/3] dt-bindings: crypto: fsl: add entropy delay
 property
Thread-Topic: [EXT] Re: [PATCH 1/3] dt-bindings: crypto: fsl: add entropy
 delay property
Thread-Index: AQHYdFB1/6ZPLK3UVkiqfeFtvvLa6a1BW74AgBELlRA=
Date:   Thu, 16 Jun 2022 17:49:30 +0000
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References: <20220530180924.1792399-1-vabhav.sharma@nxp.com>
 <20220530180924.1792399-2-vabhav.sharma@nxp.com>
 <20220605212114.GA3528129-robh@kernel.org>
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Hello Rob,

> -----Original Message-----
> From: Rob Herring <robh@kernel.org>
> Sent: Monday, June 6, 2022 2:51 AM
> To: Vabhav Sharma <vabhav.sharma@nxp.com>
> Cc: Horia Geanta <horia.geanta@nxp.com>; Gaurav Jain
> <gaurav.jain@nxp.com>; Pankaj Gupta <pankaj.gupta@nxp.com>;
> herbert@gondor.apana.org.au; davem@davemloft.net;
> shawnguo@kernel.org; linux-crypto@vger.kernel.org; linux-
> kernel@vger.kernel.org; dl-linux-imx <linux-imx@nxp.com>;
> devicetree@vger.kernel.org; linux-arm-kernel@lists.infradead.org; Silvano=
 Di
> Ninno <silvano.dininno@nxp.com>; Varun Sethi <V.Sethi@nxp.com>
> Subject: [EXT] Re: [PATCH 1/3] dt-bindings: crypto: fsl: add entropy dela=
y
> property
>=20
> Caution: EXT Email
>=20
> On Mon, May 30, 2022 at 11:39:22PM +0530, Vabhav Sharma wrote:
> > Add entropy delay property which defines the length (in system clocks)
> > of each Entropy sample taken for TRNG configuration.
> >
> > Signed-off-by: Vabhav Sharma <vabhav.sharma@nxp.com>
> > Reviewed-by: Horia Geanta <horia.geanta@nxp.com>
> > Reviewed-by: Varun Sethi <v.sethi@nxp.com>
> > ---
> >  Documentation/devicetree/bindings/crypto/fsl-sec4.txt | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/crypto/fsl-sec4.txt
> > b/Documentation/devicetree/bindings/crypto/fsl-sec4.txt
> > index 8f359f473ada..1477294eda38 100644
> > --- a/Documentation/devicetree/bindings/crypto/fsl-sec4.txt
> > +++ b/Documentation/devicetree/bindings/crypto/fsl-sec4.txt
> > @@ -62,6 +62,12 @@ PROPERTIES
> >        Definition: A standard property. Define the 'ERA' of the SEC
> >            device.
> >
> > +   - entropy-delay
> > +      Usage: optional
> > +      Value type: <u32>
> > +      Definition: A property which specifies the length (in system clo=
cks)
> > +          of each Entropy sample taken.
> > +
>=20
> Seems like this could be common, but should be a time value (with unit
> suffix) rather than clocks. If not common, then needs a vendor prefix.
> Is this time to read a value or time between values produced? Not really =
clear
> from the description.
CAAM TRNG Configuration includes 16-bit field entropy-delay. This field spe=
cifies how long the oscillator is given to freely oscillate and generate a =
single bit of entropy.
It is specified as number of system clock cycles and this u32 type field al=
ready exist in the caam driver code with default value of 3200. However, on=
 some platform this value can vary and support is added to read the value f=
rom device tree in order to override default value, Hope this helps to clar=
ify.
>=20
> Rob