On Wed, 2019-11-20 at 17:16 +0100, Stefan Wahren wrote:
> Hi Stephen,
> 
> Am 20.11.19 um 04:16 schrieb Stephen Brennan:
> > This patch series enables support for the HWRNG included on the Raspberry
> > Pi 4.  It is simply a rebase of Stefan's branch [1]. I went ahead and
> > tested this out on a Pi 4.  Prior to this patch series, attempting to use
> > the hwrng gives:
> > 
> >     $ head -c 2 /dev/hwrng
> >     head: /dev/hwrng: Input/output error
> > 
> > After this series, the same command gives two random bytes.
> 
> just a note: a more expressive test would be running rngtest (package
> rng-tools) on this device.

Just had a go at it,

root@rpi4:~# rngtest -c 1000 < /dev/hwrng
rngtest 2-unofficial-mt.14
Copyright (c) 2004 by Henrique de Moraes Holschuh
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

rngtest: starting FIPS tests...
rngtest: bits received from input: 20000032
rngtest: FIPS 140-2 successes: 998
rngtest: FIPS 140-2 failures: 2
rngtest: FIPS 140-2(2001-10-10) Monobit: 0
rngtest: FIPS 140-2(2001-10-10) Poker: 1
rngtest: FIPS 140-2(2001-10-10) Runs: 0
rngtest: FIPS 140-2(2001-10-10) Long run: 1
rngtest: FIPS 140-2(2001-10-10) Continuous run: 0
rngtest: input channel speed: (min=1.284; avg=113.786; max=126.213)Kibits/s
rngtest: FIPS tests speed: (min=17.122; avg=28.268; max=28.812)Mibits/s
rngtest: Program run time: 172323761 microseconds

AFAIR (Arch wiki) some small failures are acceptable.

Regards,
Nicolas