Index: amd64/pci/pci_cfgreg.c
===================================================================
RCS file: /usr/cvs/src/sys/amd64/pci/pci_cfgreg.c,v
retrieving revision 1.112
diff -u -r1.112 pci_cfgreg.c
--- amd64/pci/pci_cfgreg.c	10 Sep 2008 18:06:08 -0000	1.112
+++ amd64/pci/pci_cfgreg.c	11 Sep 2008 15:33:37 -0000
@@ -114,11 +114,17 @@
 static uint32_t
 pci_docfgregread(int bus, int slot, int func, int reg, int bytes)
 {
+	uint32_t val1, val2;
 
 	if (cfgmech == CFGMECH_PCIE &&
-	    (bus != 0 || !(1 << slot & pcie_badslots)))
-		return (pciereg_cfgread(bus, slot, func, reg, bytes));
-	else
+	    (bus != 0 || !(1 << slot & pcie_badslots))) {
+		val1 = pciereg_cfgread(bus, slot, func, reg, bytes);
+		val2 = pcireg_cfgread(bus, slot, func, reg, bytes);
+		if (val1 != val2)
+			panic("pci_cfgread(%d:%d:%d, %d, %d) => %#x, %#x",
+			    bus, slot, func, reg, bytes, val1, val2);
+		return (val1);
+	} else
 		return (pcireg_cfgread(bus, slot, func, reg, bytes));
 }
 
Index: i386/pci/pci_cfgreg.c
===================================================================
RCS file: /usr/cvs/src/sys/i386/pci/pci_cfgreg.c,v
retrieving revision 1.131
diff -u -r1.131 pci_cfgreg.c
--- i386/pci/pci_cfgreg.c	10 Sep 2008 18:06:08 -0000	1.131
+++ i386/pci/pci_cfgreg.c	11 Sep 2008 15:34:48 -0000
@@ -201,11 +201,17 @@
 static uint32_t
 pci_docfgregread(int bus, int slot, int func, int reg, int bytes)
 {
+	uint32_t val1, val2;
 
 	if (cfgmech == CFGMECH_PCIE &&
-	    (bus != 0 || !(1 << slot & pcie_badslots)))
-		return (pciereg_cfgread(bus, slot, func, reg, bytes));
-	else
+	    (bus != 0 || !(1 << slot & pcie_badslots))) {
+		val1 = pciereg_cfgread(bus, slot, func, reg, bytes);
+		val2 = pcireg_cfgread(bus, slot, func, reg, bytes);
+		if (val1 != val2)
+			panic("pci_cfgread(%d:%d:%d, %d, %d) => %#x, %#x",
+			    bus, slot, func, reg, bytes, val1, val2);
+		return (val1);
+	} else
 		return (pcireg_cfgread(bus, slot, func, reg, bytes));
 }