adding support for irq-based entropy addition (comments requested)

Currently in the 2.2 kernel there is no support for collecting entropy based on
interrupts, and the entropy measurement that we do have for ppc is based on
jiffies.

I've included two patches against the stock kernel.org 2.2.19, with are related
but independent (although the second one would really be best if the first is
also applied).

The first patch adds support for higher precision timing using the timebase
register on machines where CONFIG_6xx is defined.  Since the PPC601 doesn't
support this, I've added a flag to let us know if the timebase registers are
present.  If this flag already exists somewhere I'd love to know so that I can
get rid of this addition. This patch affects all existing measurements of
entropy.

The second patch adds support for collecting entropy from the timing of irqs
that have set the SA_SAMPLE_RANDOM flag.  This could be useful for headless
devices, as it enables the collection of entropy from network traffic.  There is
currently a discussion as to the safety of this on the lkml, but in some cases
there is little other choice.

Any comments are welcome.

Chris

--
Chris Friesen                    | MailStop: 043/33/F10
Nortel Networks                  | work: (613) 765-0557
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