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Commit 01c9348c authored by Paul Mackerras's avatar Paul Mackerras Committed by Michael Ellerman
Browse files

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: default avatarPaul Mackerras <paulus@samba.org>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent 1c2cb594

arch/powerpc/include/asm/archrandom.h

+14 −14
Original line number Diff line number Diff line
@@ -7,13 +7,22 @@ 


static inline int arch_get_random_long(unsigned long *v)

{

	if (ppc_md.get_random_long)

		return ppc_md.get_random_long(v);



	return 0;

}



static inline int arch_get_random_int(unsigned int *v)

{

	return 0;

}



static inline int arch_get_random_seed_long(unsigned long *v)

{

	if (ppc_md.get_random_seed)

		return ppc_md.get_random_seed(v);



	return 0;

}

static inline int arch_get_random_seed_int(unsigned int *v)

{

	unsigned long val;

	int rc;
@@ -26,23 +35,14 @@ static inline int arch_get_random_int(unsigned int *v) 
}



static inline int arch_has_random(void)

{

	return !!ppc_md.get_random_long;

}



static inline int arch_get_random_seed_long(unsigned long *v)

{

	return 0;

}

static inline int arch_get_random_seed_int(unsigned int *v)

{

	return 0;

}



static inline int arch_has_random_seed(void)

{

	return 0;

	return !!ppc_md.get_random_seed;

}



#endif /* CONFIG_ARCH_RANDOM */



#ifdef CONFIG_PPC_POWERNV

arch/powerpc/include/asm/machdep.h

+1 −1
Original line number Diff line number Diff line
@@ -249,7 +249,7 @@ struct machdep_calls { 
#endif



#ifdef CONFIG_ARCH_RANDOM

	int (*get_random_long)(unsigned long *v);

	int (*get_random_seed)(unsigned long *v);

#endif

};

arch/powerpc/platforms/powernv/rng.c

+1 −1
Original line number Diff line number Diff line
@@ -128,7 +128,7 @@ static __init int rng_create(struct device_node *dn) 


	pr_info_once("Registering arch random hook.\n");



	ppc_md.get_random_long = powernv_get_random_long;

	ppc_md.get_random_seed = powernv_get_random_long;



	return 0;

}

arch/powerpc/platforms/pseries/rng.c

+1 −1
Original line number Diff line number Diff line
@@ -38,7 +38,7 @@ static __init int rng_init(void) 


	pr_info("Registering arch random hook.\n");



	ppc_md.get_random_long = pseries_get_random_long;

	ppc_md.get_random_seed = pseries_get_random_long;



	return 0;

}