--- e6ec8a2df1c368fa3a0cfd5b8db62076b1157c44
+++ 1a2d4b19eb23380babc97f401355a39d43dd79cf
@@ -102,11 +102,16 @@ int use_calgary __read_mostly = 0;
 #define PMR_SOFTSTOPFAULT	0x40000000
 #define PMR_HARDSTOP		0x20000000
 
-#define MAX_NUM_OF_PHBS		8 /* how many PHBs in total? */
-#define MAX_NUM_CHASSIS		8 /* max number of chassis */
-/* 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
+/*
+ * The maximum PHB bus number.
+ * x3950M2 (rare): 8 chassis, 48 PHBs per chassis = 384
+ * x3950M2: 4 chassis, 48 PHBs per chassis        = 192
+ * x3950 (PCIE): 8 chassis, 32 PHBs per chassis   = 256
+ * x3950 (PCIX): 8 chassis, 16 PHBs per chassis   = 128
+ */
+#define MAX_PHB_BUS_NUM		256
+
+#define PHBS_PER_CALGARY	  4
 
 /* register offsets in Calgary's internal register space */
 static const unsigned long tar_offsets[] = {
@@ -1053,8 +1058,6 @@ static int __init calgary_init_one(struc
 	struct iommu_table *tbl;
 	int ret;
 
-	BUG_ON(dev->bus->number >= MAX_PHB_BUS_NUM);
-
 	bbar = busno_to_bbar(dev->bus->number);
 	ret = calgary_setup_tar(dev, bbar);
 	if (ret)