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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" 
        <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: AQHYdFB1/6ZPLK3UVkiqfeFtvvLa6a1BW74AgBELlRCAFK2ygIJxmDvQ
Date:   Tue, 1 Aug 2023 23:21:27 +0000
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Hello Rob,

> -----Original Message-----
> From: Rob Herring <robh@kernel.org>
> Sent: Thursday, June 30, 2022 2:56 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: Re: [EXT] Re: [PATCH 1/3] dt-bindings: crypto: fsl: add entropy =
delay
> property
>=20
> Caution: EXT Email
>=20
> On Thu, Jun 16, 2022 at 05:49:30PM +0000, Vabhav Sharma wrote:
> > 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
> > > delay property
> > >
> > > Caution: EXT Email
> > >
> > > 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=
 clocks)
> > > > +          of each Entropy sample taken.
> > > > +
> > >
> > > 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
> specifies how long the oscillator is given to freely oscillate and genera=
te a
> single bit of entropy.
> > It is specified as number of system clock cycles and this u32 type fiel=
d
> already 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
> from device tree in order to override default value, Hope this helps to c=
larify.
> =09
> So that is how often a sample can be read? Or what happens if you read a
> sample too quick (in less than this delay time)?
This is the fixed value that will work always profiled while offline per So=
C or SoC family.
Value will work during initialization and run time.

Apologize to miss the email and delayed reply.
>=20
> Look at other h/w and drivers see if something common makes sense here.
>=20
> Rob