linux-kernel - Re: [PATCH 0/3] enable CAAM's HWRNG as default

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Message-ID: <226f5a669c2199408abcdec0ccddc9ff05672631.camel@pengutronix.de>
Date:   Tue, 29 Oct 2019 17:43:30 +0100
From:   Lucas Stach <l.stach@...gutronix.de>
To:     Andrey Smirnov <andrew.smirnov@...il.com>,
        linux-crypto@...r.kernel.org
Cc:     Chris Healy <cphealy@...il.com>,
        Horia Geantă <horia.geanta@....com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Iuliana Prodan <iuliana.prodan@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] enable CAAM's HWRNG as default

On Di, 2019-10-29 at 09:29 -0700, Andrey Smirnov wrote:
> Everyone:
> 
> This series is a continuation of original [discussion]. I don't know
> if what's in the series is enough to use CAAMs HWRNG system wide, but
> I am hoping that with enough iterations and feedback it will be.
> 
> Feedback is welcome!

I'm not sure if we can ever use the job based RNG interface to hook it
up to the Linux HWRNG interface. After all the job based RNG interface
is always a DRNG, which only gets seeded by the TRNG. The reseed
interval is given in number of clock cycles, so there is no clear
correlation between really true random input bits and the number of
DRNG output bits.

I've hacked up some proof of concept code which uses the TRNG access in
the control interface to get the raw TRNG random bits. This seems to
yield about 6400 bit/s of true entropy. It may be better to use this
interface to hook up to the Linux HWRNG framework.

Regards,
Lucas