linux-kernel - Re: [PATCH v1] crypto: caam

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Date:   Wed, 19 Jul 2017 20:13:03 +0200
From:   Oleksij Rempel <ore@...gutronix.de>
To:     Horia Geantă <horia.geanta@....com>
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Harald Freudenberger <freude@...ux.vnet.ibm.com>,
        Oleksij Rempel <o.rempel@...gutronix.de>,
        Dan Douglass <dan.douglass@....com>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH v1] crypto: caam - set hwrng quality level

On Wed, Jul 19, 2017 at 04:53:21PM +0000, Horia Geantă wrote:
> On 7/19/2017 7:32 PM, Oleksij Rempel wrote:
> > On Wed, Jul 19, 2017 at 12:49:47PM +0000, Horia Geantă wrote:
> >> On 7/19/2017 10:45 AM, Oleksij Rempel wrote:
> >>> According documentation, it is NIST certified TRNG.
> >>> So, set high quality to let the HWRNG framework automatically use it.
> >>>
> >>> Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
> >>> ---
> >>>  drivers/crypto/caam/caamrng.c | 6 ++++++
> >>>  1 file changed, 6 insertions(+)
> >>>
> >>> diff --git a/drivers/crypto/caam/caamrng.c b/drivers/crypto/caam/caamrng.c
> >>> index 41398da3edf4..684c0bc88dfd 100644
> >>> --- a/drivers/crypto/caam/caamrng.c
> >>> +++ b/drivers/crypto/caam/caamrng.c
> >>> @@ -292,10 +292,16 @@ static int caam_init_rng(struct caam_rng_ctx *ctx, struct device *jrdev)
> >>>  	return 0;
> >>>  }
> >>>  
> >>> +/*
> >>> + * hwrng register struct
> >>> + * The trng is suppost to have 100% entropy, and thus
> >>> + * we register with a very high quality value.
> >>> + */
> >>>  static struct hwrng caam_rng = {
> >>>  	.name		= "rng-caam",
> >>>  	.cleanup	= caam_cleanup,
> >>>  	.read		= caam_read,
> >>> +	.quality	= 999,
> >>
> >> Why not 1024, i.e. where is 999 coming from?
> > 
> > It comes from s390-trng.c driver.
> > Should I use 1024 instead?
> > 
> AFAICT the range for quality is from 0 to 1024 (no entropy -> perfect
> entropy).
> 
> 1024 should be used since I'd expect a HW TRNG to provide perfect
> entropy unless otherwise stated.

I assume 1024 can be given only on verified HW with accessible verilog
files and compared with resulting chip :)
May be this would be a good example https://www.sifive.com/

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