powerpc: Use hardware RNG for arch_get_random_seed_* not arch_get_random_*
authorPaul Mackerras <paulus@samba.org>
Fri, 17 Jul 2015 10:11:43 +0000 (20:11 +1000)
committerMichael Ellerman <mpe@ellerman.id.au>
Thu, 23 Jul 2015 09:52:03 +0000 (19:52 +1000)
commit01c9348c7620ec650aaeb3ce339f614709b2fb5a
tree519bbfcb73d48637750357676b3f024761dfa68d
parent1c2cb594441d02815d304cccec9742ff5c707495
powerpc: Use hardware RNG for arch_get_random_seed_* not arch_get_random_*

The hardware RNG on POWER8 and POWER7+ can be relatively slow, since
it can only supply one 64-bit value per microsecond.  Currently we
read it in arch_get_random_long(), but that slows down reading from
/dev/urandom since the code in random.c calls arch_get_random_long()
for every longword read from /dev/urandom.

Since the hardware RNG supplies high-quality entropy on every read, it
matches the semantics of arch_get_random_seed_long() better than those
of arch_get_random_long().  Therefore this commit makes the code use
the POWER8/7+ hardware RNG only for arch_get_random_seed_{long,int}
and not for arch_get_random_{long,int}.

This won't affect any other PowerPC-based platforms because none of
them currently support a hardware RNG.  To make it clear that the
ppc_md function pointer is used for arch_get_random_seed_*, we rename
it from get_random_long to get_random_seed.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
arch/powerpc/include/asm/archrandom.h
arch/powerpc/include/asm/machdep.h
arch/powerpc/platforms/powernv/rng.c
arch/powerpc/platforms/pseries/rng.c