[PATCH v2 2/2] Port to new board "VoCore2"

[Mauro Condarelli]

Thanks Daniel.

On 1/7/20 4:58 PM, Daniel Schwierzeck wrote:
> On Tue, Jan 7, 2020 at 3:30 PM Mauro Condarelli <mc5686 at mclink.it> wrote:
> ...
>> I also have problems with entropy pool in Linux, do you happen to know
>> if (and how) MT7628 supports HWRNG?
> what problems exactly?
Currently it takes a LOT of time to fill-up the entropy pool
(over half an hour) and on first startup, when it has to
generate ssh keys and other stuff system is virtually dead
for that long.
>
> On a embedded device you usually can only add randomness from
> interrupts sources to the entropy pool
> due to lack of disk or input devices. On a router the most interrupts
> are typically generated by drivers
> for ethernet and SPI/NAND/MMC controllers. You could use user-space
> daemons like haveged [1]
> to add more randomness from hardware events.
I tried that and it helps.
I also found *traces* pointing in the direction of hardware
support for RNG in my SoC; I have ca opy of the (badly
incomplete) "MT7628 PROGRAMMING GUIDE" and it
reports in "PWM1 Control register" an "interesting" field:
RESV1 Select Random Generator mode.
This males a lot of sense because this SoC is meant to implement
Wireless routers, so crypto and random acceleration would
be very useful.
Unfortunately I don't have more precise information, hence
the question.

> Also have a look at the documentation in Linux's drivers/char/random.c
> for more information, especially
> the paragraph "Ensuring unpredictability at system startup".
>
> PS: In my day job (embedded router devices) I use a hash like SHA256
> over the U-Boot MTD partition
> where also some device specific information like MAC addresses and
> serial numbers are stored to generate
> the initial seed for the entropy pool on first boot. Afterwards I
> manage the random seed over reboots as
> described in drivers/char/random.c.
>
> [1] https://linux.die.net/man/8/haveged
>