powerpc/vphn: clarify the H_HOME_NODE_ASSOCIATIVITY API

The number of values returned by the H_HOME_NODE_ASSOCIATIVITY h_call deserves
to be explicitly defined, for a better understanding of the code.
Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/mm/numa.c

@@ -1247,11 +1247,15 @@ static int update_cpu_associativity_changes_mask(void)
 	return cpumask_weight(changes);
 }
 
+/* The H_HOME_NODE_ASSOCIATIVITY h_call returns 6 64-bit registers.
+ */
+#define VPHN_REGISTER_COUNT 6
+
 /*
  * 6 64-bit registers unpacked into 12 32-bit associativity values. To form
  * the complete property we have to add the length in the first cell.
  */
-#define VPHN_ASSOC_BUFSIZE (6*sizeof(u64)/sizeof(u32) + 1)
+#define VPHN_ASSOC_BUFSIZE (VPHN_REGISTER_COUNT*sizeof(u64)/sizeof(u32) + 1)
 
 /*
  * Convert the associativity domain numbers returned from the hypervisor
@@ -1309,7 +1313,7 @@ static long hcall_vphn(unsigned long cpu, __be32 *associativity)
 	int i;
 
 	rc = plpar_hcall9(H_HOME_NODE_ASSOCIATIVITY, retbuf, flags, hwcpu);
-	for (i = 0; i < 6; i++)
+	for (i = 0; i < VPHN_REGISTER_COUNT; i++)
 		retbuf[i] = cpu_to_be64(retbuf[i]);
 	vphn_unpack_associativity(retbuf, associativity);