powerpc: Use hardware RNG for arch_get_random_seed_* not arch_get_random_*

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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>

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This commit is contained in:

Paul Mackerras 2015-07-17 20:11:43 +10:00 • committed by Michael Ellerman

parent 1c2cb59444

commit 01c9348c76

4 changed files with 17 additions and 17 deletions

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28

arch/powerpc/include/asm/archrandom.h

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arch/powerpc/include/asm/machdep.h

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2

arch/powerpc/platforms/powernv/rng.c

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2

arch/powerpc/platforms/pseries/rng.c

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