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

@@ -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

@@ -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

@@ -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

@@ -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;
 }