want the NO_ESTIMATE flag here, because if the source doesn't have it,
rnd_add_data will *use the time the data was added directly as entropy*,
which is not a good idea either for a hardware RNG that works like this
one (periodically polled by the driver) or, really, like any other that I've
seen, because even for "interrupt when ready" RNGs the data rate (and thus
interrupt time) will vary only slightly for a given RNG configuration over
time, if at all.
The data we add _is_ counted into the pool estimage because we directly
pass in an entropy estimate.
The overloading of the NO_ESTIMATE flag with this meaning seems, to me, like
a design bug (albeit easily fixed) in the rng interface; but until that's
changed, we need to use it here.
means "count", in this context) the entropy we're adding because we poll the
device periodically. Sure, we poll it periodically, but it's a hardware
RNG -- the data returned should be random no matter when we read the
register!
tls