random: Add arch_has_random[_seed]()

Add predicate functions for having arch_get_random[_seed]*().  The
only current use is to avoid the loop in arch_random_refill() when
arch_get_random_seed_long() is unavailable.
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

arch/powerpc/include/asm/archrandom.h

@@ -25,6 +25,11 @@ static inline int arch_get_random_int(unsigned int *v)
 	return rc;
 }
 
+static inline int arch_has_random(void)
+{
+	return !!ppc_md.get_random_long;
+}
+
 int powernv_get_random_long(unsigned long *v);
 
 static inline int arch_get_random_seed_long(unsigned long *v)
@@ -35,6 +40,10 @@ static inline int arch_get_random_seed_int(unsigned int *v)
 {
 	return 0;
 }
+static inline int arch_has_random_seed(void)
+{
+	return 0;
+}
 
 #endif /* CONFIG_ARCH_RANDOM */
 

arch/x86/include/asm/archrandom.h

@@ -114,6 +114,9 @@ GET_SEED(arch_get_random_seed_int, unsigned int, RDSEED_INT, ASM_NOP4);
 
 #endif /* CONFIG_X86_64 */
 
+#define arch_has_random()	static_cpu_has(X86_FEATURE_RDRAND)
+#define arch_has_random_seed()	static_cpu_has(X86_FEATURE_RDSEED)
+
 #else
 
 static inline int rdrand_long(unsigned long *v)

drivers/char/random.c

@@ -1307,6 +1307,9 @@ static int arch_random_refill(void)
 	unsigned int i;
 	unsigned long buf[nlongs];
 
+	if (!arch_has_random_seed())
+		return 0;
+
 	for (i = 0; i < nlongs; i++) {
 		if (arch_get_random_seed_long(&buf[n]))
 			n++;

include/linux/random.h

@@ -88,6 +88,10 @@ static inline int arch_get_random_int(unsigned int *v)
 {
 	return 0;
 }
+static inline int arch_has_random(void)
+{
+	return 0;
+}
 static inline int arch_get_random_seed_long(unsigned long *v)
 {
 	return 0;
@@ -96,6 +100,10 @@ static inline int arch_get_random_seed_int(unsigned int *v)
 {
 	return 0;
 }
+static inline int arch_has_random_seed(void)
+{
+	return 0;
+}
 #endif
 
 /* Pseudo random number generator from numerical recipes. */