pata_sil680: only enable MMIO on Cell blades

There have been reported regressions of the SIL 680 driver when using MMIO, so
this makes it only try MMIO on Cell blades where it's known to be necessary
(the host bridge doesn't do PIO on these).

We'll try to find the root problem with MMIO separately.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Alan Cox <alan@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

drivers/ata/pata_sil680.c

@@ -269,7 +269,11 @@ static u8 sil680_init_chip(struct pci_dev *pdev, int *try_mmio)
 	dev_dbg(&pdev->dev, "sil680: BA5_EN = %d clock = %02X\n",
 		tmpbyte & 1, tmpbyte & 0x30);
 
-	*try_mmio = (tmpbyte & 1) || pci_resource_start(pdev, 5);
+	*try_mmio = 0;
+#ifdef CONFIG_PPC
+	if (machine_is(cell))
+		*try_mmio = (tmpbyte & 1) || pci_resource_start(pdev, 5);
+#endif
 
 	switch(tmpbyte & 0x30) {
 		case 0x00: