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linux-next/arch/powerpc/platforms/pseries/rng.c
Paul Mackerras 01c9348c76 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>
2015-07-23 19:52:03 +10:00

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C

/*
* Copyright 2013, Michael Ellerman, IBM Corporation.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*/
#define pr_fmt(fmt) "pseries-rng: " fmt
#include <linux/kernel.h>
#include <linux/of.h>
#include <asm/archrandom.h>
#include <asm/machdep.h>
#include <asm/plpar_wrappers.h>
static int pseries_get_random_long(unsigned long *v)
{
unsigned long retbuf[PLPAR_HCALL_BUFSIZE];
if (plpar_hcall(H_RANDOM, retbuf) == H_SUCCESS) {
*v = retbuf[0];
return 1;
}
return 0;
}
static __init int rng_init(void)
{
struct device_node *dn;
dn = of_find_compatible_node(NULL, NULL, "ibm,random");
if (!dn)
return -ENODEV;
pr_info("Registering arch random hook.\n");
ppc_md.get_random_seed = pseries_get_random_long;
return 0;
}
machine_subsys_initcall(pseries, rng_init);