On G5 machines, we remap the AGP port to bus number 0xf0. XFree

contains a hack that is unfixable at the moment for getting the
IO base which is hard coded to bus number 0 (AGP on earlier machines).
We work around this by passing the IO base of bus 0xf0 when asked
for bus 0 in pciconfig_iobase on those machines. Bus 0 is the HT
root and has no IOs, so that is safe.

arch/ppc/kernel/pci.c

@@ -1645,12 +1645,23 @@ pci_bus_to_phys(unsigned int ba, int busnr)
  * Note that the returned IO or memory base is a physical address
  */
 
-long
-sys_pciconfig_iobase(long which, unsigned long bus, unsigned long devfn)
+long sys_pciconfig_iobase(long which, unsigned long bus, unsigned long devfn)
 {
-	struct pci_controller* hose = pci_bus_to_hose(bus);
+	struct pci_controller* hose;
 	long result = -EOPNOTSUPP;
 
+	/* Argh ! Please forgive me for that hack, but that's the
+	 * simplest way to get existing XFree to not lockup on some
+	 * G5 machines... So when something asks for bus 0 io base
+	 * (bus 0 is HT root), we return the AGP one instead.
+	 */
+#ifdef CONFIG_PPC_PMAC
+	if (_machine == _MACH_Pmac && machine_is_compatible("MacRISC4"))
+		if (bus == 0)
+			bus = 0xf0;
+#endif /* CONFIG_PPC_PMAC */
+
+	hose = pci_bus_to_hose(bus);
 	if (!hose)
 		return -ENODEV;