linux-kernel - Re: [PATCH v2 1/2] hwrng: iproc-rng200

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Message-ID: <3322411.JsYv2Y6bm7@tauon.chronox.de>
Date:   Wed, 20 May 2020 14:11:34 +0200
From:   Stephan Mueller <smueller@...onox.de>
To:     Krzysztof Kozlowski <krzk@...nel.org>
Cc:     Lukasz Stelmach <l.stelmach@...sung.com>,
        Matt Mackall <mpm@...enic.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        bcm-kernel-feedback-list@...adcom.com,
        Kukjin Kim <kgene@...nel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Markus Elfring <elfring@...rs.sourceforge.net>,
        Matthias Brugger <mbrugger@...e.com>,
        Stefan Wahren <wahrenst@....net>, linux-crypto@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-samsung-soc@...r.kernel.org" 
        <linux-samsung-soc@...r.kernel.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [PATCH v2 1/2] hwrng: iproc-rng200 - Set the quality value

Am Mittwoch, 20. Mai 2020, 14:00:01 CEST schrieb Krzysztof Kozlowski:

Hi Krzysztof,

> On Wed, 20 May 2020 at 13:53, Stephan Mueller <smueller@...onox.de> wrote:
> > > > That said, the illustrated example is typical for hardware RNGs. Yet
> > > > it is never guaranteed to work that way. Thus, if you can point to
> > > > architecture documentation of your specific hardware RNGs showing that
> > > > the data read from the hardware is pure unconditioned noise data, then
> > > > I have no objections to the patch.
> > > 
> > > I can tell for sure that this is the case for exynos-trng[1].
> > 
> > So you are saying that the output for the exynos-trng is straight from a
> > ring oscillator without any post-processing of any kind?
> 
> Hi,
> 
> I think we will never be able to state this because the manual is
> quite limited in sharing internals. What the driver does and probably
> Lukasz wanted to say is that there is "post processing" block and
> feature which can be disabled. The manual is saying the TRNG block
> generates random data from thermal noise but not how much in a direct
> way. There could be some simple post-processing or not (except the one
> able to on/off). Also manual says this post processing block is there
> to remove statistical weakness from the TRNG block. To me it does not
> prove enough that raw data is really raw...

Unterstood, but can't that statement be added to the commit message?
> 
> Best regards,
> Krzysztof


Ciao
Stephan