linux-kernel - Re: [PATCH] hwrng: bcm2835: set quality to 1000

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Date:   Thu, 11 Mar 2021 20:52:20 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Álvaro Fernández Rojas <noltari@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Stephan Mueller <smueller@...onox.de>
Cc:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Andrew Lunn <andrew@...n.ch>, Matt Mackall <mpm@...enic.com>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        bcm-kernel-feedback-list@...adcom.com,
        Rikard Falkeborn <rikard.falkeborn@...il.com>,
        linux-crypto@...r.kernel.org, linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Stijn Tintel <stijn@...ux-ipv6.be>, ynezz@...e.cz
Subject: Re: [PATCH] hwrng: bcm2835: set quality to 1000



On 3/4/2021 10:26 PM, Álvaro Fernández Rojas wrote:
> Hi Florian,
> 
>> El 4 mar 2021, a las 23:28, Florian Fainelli <f.fainelli@...il.com> escribió:
>>
>> On 3/4/21 7:11 AM, Nicolas Saenz Julienne wrote:
>>> On Wed, 2021-03-03 at 10:29 +0100, Álvaro Fernández Rojas wrote:
>>>> Hi Herbert,
>>>>
>>>>> El 3 mar 2021, a las 10:20, Herbert Xu <herbert@...dor.apana.org.au> escribió:
>>>>>
>>>>> On Sat, Feb 20, 2021 at 08:12:45PM +0100, Álvaro Fernández Rojas wrote:
>>>>>>
>>>>>> I ran rngtest and this is what I got:
>>>>>
>>>>> This is meaningless except for sources that have not been whitened.
>>>>>
>>>>> Your justification needs to be based on what the hardware does or
>>>>> is documented to do.
>>>>
>>>> Ok, so I guess that we’re never setting that value to anything since there’s
>>>> no public documentation about that ¯\_(ツ)_/¯.
>>>
>>> @Florian, is there a way you might be able to get the official value?
>>
>> I will be looking into the documentation this weekend and let you know
>> whether we can change the driver's quality accordingly.
> 
> Could you do that for iproc-rng200.c too?

>From looking at some documentation and the design of the 6368 RNG which
is supposedly the same as the Raspberry Pi 1/2/3 RNG, this appears to be
a random number generator that does not go through any post-processing
and just collects random bits into a FIFO.

The rbg200 is also similar except that it is integrated into a wrapper
called the rng200 which supposedly only accepts data that has passed
"NIST industry standard random data quality algorithm" without being
specific. So it seems to me you may be able to set the quality field for
bcm2835-rng, but not for iproc-rng200.

Stephan does that sound right?
-- 
Florian