linux-kernel - Re: [PATCH v4 2/2] crypto: hw_random

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Date:   Mon, 10 Apr 2017 12:12:03 +0200
From:   Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
To:     Krzysztof Kozlowski <krzk@...nel.org>
Cc:     James Hogan <james.hogan@...tec.com>,
        Matt Mackall <mpm@...enic.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Kukjin Kim <kgene@...nel.org>,
        Javier Martinez Canillas <javier@....samsung.com>,
        "David S. Miller" <davem@...emloft.net>,
        Dave Airlie <airlied@...hat.com>,
        David Airlie <airlied@...ux.ie>,
        Bernie Thompson <bernie@...gable.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        PrasannaKumar Muralidharan <prasannatsmkumar@...il.com>,
        linux-kernel@...r.kernel.org, linux-metag@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-fbdev@...r.kernel.org,
        Stephan Müller <smueller@...onox.de>
Subject: Re: [PATCH v4 2/2] crypto: hw_random - Add new Exynos RNG driver


Hi,

On Saturday, April 08, 2017 03:32:45 PM Krzysztof Kozlowski wrote:
> Replace existing hw_ranndom/exynos-rng driver with a new, reworked one.
> This is a driver for pseudo random number generator block which on
> Exynos4 chipsets must be seeded with some value.  On newer Exynos5420
> chipsets it might seed itself from true random number generator block
> but this is not implemented yet.
> 
> New driver is a complete rework to use the crypto ALGAPI instead of
> hw_random API.  Rationale for the change:
> 1. hw_random interface is for true RNG devices.
> 2. The old driver was seeding itself with jiffies which is not a
>    reliable source for randomness.
> 3. Device generates five random 32-bit numbers in each pass but old
>    driver was returning only one 32-bit number thus its performance was
>    reduced.
> 
> Compatibility with DeviceTree bindings is preserved.
> 
> New driver does not use runtime power management but manually enables
> and disables the clock when needed.  This is preferred approach because
> using runtime PM just to toggle clock is huge overhead.
> 
> Another difference is reseeding itself with generated random data
> periodically and during resuming from system suspend (previously driver
> was re-seeding itself again with jiffies).
> 
> Signed-off-by: Krzysztof Kozlowski <krzk@...nel.org>
> Reviewed-by: Stephan Müller <smueller@...onox.de>
> Reviewed-by: PrasannaKumar Muralidharan <prasannatsmkumar@...il.com>

Reviewed-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics