diff --git a/arch/x86_64/kernel/pci-calgary.c b/arch/x86_64/kernel/pci-calgary.c
index cd866135e4ef5d0e6ede8ba7a3380d353178420a..466588f956013233942e07d9e4287e6caf871430 100644
--- a/arch/x86_64/kernel/pci-calgary.c
+++ b/arch/x86_64/kernel/pci-calgary.c
@@ -86,7 +86,8 @@
 
 #define MAX_NUM_OF_PHBS		8 /* how many PHBs in total? */
 #define MAX_NUM_CHASSIS		8 /* max number of chassis */
-#define MAX_PHB_BUS_NUM		(MAX_NUM_OF_PHBS * MAX_NUM_CHASSIS * 2) /* max dev->bus->number */
+/* MAX_PHB_BUS_NUM is the maximal possible dev->bus->number */
+#define MAX_PHB_BUS_NUM		(MAX_NUM_OF_PHBS * MAX_NUM_CHASSIS * 2)
 #define PHBS_PER_CALGARY	4
 
 /* register offsets in Calgary's internal register space */