Re: RND_TYPE_RNG question concerning rate of random bits production

[Taylor R Campbell <campbell+netbsd-tech-kern%mumble.net@localhost>]

   Date: Mon, 27 Jan 2014 13:05:58 -0600
   From: Frank Zerangue <frank.zerangue%gmail.com@localhost>

   I looked at hifn, amdpm, and bcm28335 RNG drivers and they all seem
   to do the same. They setup a callout to periodically call there RNG
   reader to prime the random pool with more bits; but I don't see how
   the polling is based on entropy needed. Could you clarify for me
   what I have missed in regard to your suggestion below.

Perhaps you're not looking at the code in HEAD.  See, e.g.,

http://nxr.netbsd.org/xref/src/sys/arch/arm/broadcom/bcm2835_rng.c#128

which sets up a callback so that when the system thinks it needs some
more entropy, it will call bcmrng_get_cb, which schedules a softintr
to actually read data from the hardware and feed it to the system
entropy pool.

This API is not yet stable -- at least, some months ago, Thor and I
discussed changing it to render the softintr indirection and locking
dance unnecessary -- but it will work for now.