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From:   Fabio Estevam <festevam@gmail.com>
Date:   Tue, 11 Jan 2022 15:34:49 -0300
Message-ID: <CAOMZO5DUwg2ppLFMkzCYGA652j1Q6pcTuEnUEyTNGv7_rZLhQA@mail.gmail.com>
Subject: Re: [PATCH] crypto: caam - enable prediction resistance conditionally
To:     Andrey Smirnov <andrew.smirnov@gmail.com>
Cc:     Herbert Xu <herbert@gondor.apana.org.au>,
        =?UTF-8?Q?Horia_Geant=C4=83?= <horia.geanta@nxp.com>,
        Andrei Botila <andrei.botila@nxp.com>,
        Fredrik Yhlen <fredrik.yhlen@endian.se>,
        Heiko Schocher <hs@denx.de>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@vger.kernel.org>, Fabio Estevam <festevam@denx.de>
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Hi Andrey,

On Tue, Jan 11, 2022 at 3:21 PM Andrey Smirnov <andrew.smirnov@gmail.com> wrote:

> Is this true for every i.MX device? I haven't worked with the

I do see the problem on i.MX6SX.

This thread reports the same problem on i.MX6D:
https://www.spinics.net/lists/linux-crypto/msg52319.html

> i.MX6Q/i.MX8 hardware I was enabling this feature for in a while, so
> I'm not 100% up to date on all of the problems we've seen with those,
> but last time enabling prediction resistance didn't seem to cause any
> issues besides a noticeable slowdown of random data generation.
>
> Can this be a Kconfig option or maybe a runtime flag so that it'd
> still be possible for some i.MX users to keep PR enabled?

The problem is that I don't know when it is safe or not to enable PR.

What about introducing a boolean devicetree property that when
present, disables prediction resistance?