JZ4780 RNG and entropy depletion

JZ4780 RNG and entropy depletion

[Jeffrey Walton]

Hi Everyone,

I have a MIPSEL ci20 dev board for testing. The board has a hardware
based rng, but its suffering entropy depletion. I have Debian's
rng-tools package installed.

The board lacks /dev/hwrng. /dev/random blocks indefinitely after
draining the device. "Indefinitely" may not be accurate, but I killed
a program that waited over 4 hours for 16 bytes after draining
/dev/random.

The ci20's documentation is a bit scant, but it can be found at
http://mipscreator.imgtec.com/CI20/hardware/soc/JZ4780_PM.pdf. I'm not
sure what the output rate is, but it seems to be capable of one
machine word (4 bytes) every few milliseconds. Without a delay, I can
see values being shifted into the register mapped at 0x100000DC.

I have a few questions:

  * Is there a driver for JZ4780 rng?
  * Is there a particular package for the driver that needs to be installed?
  * What causes/triggers /dev/hwrng to replenish /dev/random?

Thanks in advance.

Jeff

Re: JZ4780 RNG and entropy depletion

[Stephan Mueller]

Am Sonntag, 14. August 2016, 01:33:32 CEST schrieb Jeffrey Walton:

Hi Jeffrey,

> Hi Everyone,
> 
> I have a MIPSEL ci20 dev board for testing. The board has a hardware
> based rng, but its suffering entropy depletion. I have Debian's
> rng-tools package installed.
> 
> The board lacks /dev/hwrng. /dev/random blocks indefinitely after
> draining the device. "Indefinitely" may not be accurate, but I killed
> a program that waited over 4 hours for 16 bytes after draining
> /dev/random.
> 
> The ci20's documentation is a bit scant, but it can be found at
> http://mipscreator.imgtec.com/CI20/hardware/soc/JZ4780_PM.pdf. I'm not
> sure what the output rate is, but it seems to be capable of one
> machine word (4 bytes) every few milliseconds. Without a delay, I can
> see values being shifted into the register mapped at 0x100000DC.
> 
> I have a few questions:
> 
>   * Is there a driver for JZ4780 rng?

What is the PCI ID?

>   * Is there a particular package for the driver that needs to be installed?
> * What causes/triggers /dev/hwrng to replenish /dev/random?

Using rngd which is triggered by /dev/random automatically when its entropy 
level falls below a threshold.

Ciao
Stephan