[POWERPC] Maple U3 HT - reject inappropriate config space access

When there is a PCI-X mode 2 capable device behind the HT<->PCI-X
bridge, the pci core decides that the device has the extended 4K
config space, even though the bus is not operating in mode 2.  This is
because the u3_ht pci ops silently accept offsets greater than 255 but
use only the 8 least significant bits, which means reading at offset
0x100 gets the data at offset 0x0, and causes confusion for lspci.

Reject accesses to configuration space offsets greater than 255.

Signed-off-by: Nathan Lynch <ntl@pobox.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/platforms/maple/pci.c

@@ -213,6 +213,9 @@ static int u3_ht_read_config(struct pci_bus *bus, unsigned int devfn,
 	if (hose == NULL)
 		return PCIBIOS_DEVICE_NOT_FOUND;
 
+	if (offset > 0xff)
+		return PCIBIOS_BAD_REGISTER_NUMBER;
+
 	addr = u3_ht_cfg_access(hose, bus->number, devfn, offset);
 	if (!addr)
 		return PCIBIOS_DEVICE_NOT_FOUND;
@@ -245,6 +248,9 @@ static int u3_ht_write_config(struct pci_bus *bus, unsigned int devfn,
 	if (hose == NULL)
 		return PCIBIOS_DEVICE_NOT_FOUND;
 
+	if (offset > 0xff)
+		return PCIBIOS_BAD_REGISTER_NUMBER;
+
 	addr = u3_ht_cfg_access(hose, bus->number, devfn, offset);
 	if (!addr)
 		return PCIBIOS_DEVICE_NOT_FOUND;