ahci: don't attach if ICH6 is in combined mode

ICH6 R/Ms share PCI ID between piix and ahci modes and we've been
allowing ahci to attach regardless of how BIOS configured it.
However, enabling AHCI mode when the controller is in combined mode
can result in unexpected behavior.  Don't attach if the controller is
in combined mode.
Signed-off-by: Tejun Heo <htejun@gmail.com>
Cc: Bill Nottingham <notting@redhat.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

drivers/ata/ahci.c

@@ -193,6 +193,8 @@ enum {
 					  ATA_FLAG_ACPI_SATA | ATA_FLAG_AN |
 					  ATA_FLAG_IPM,
 	AHCI_LFLAG_COMMON		= ATA_LFLAG_SKIP_D2H_BSY,
+
+	ICH_MAP				= 0x90, /* ICH MAP register */
 };
 
 struct ahci_cmd_hdr {
@@ -2273,6 +2275,22 @@ static int ahci_init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
 	if (rc)
 		return rc;
 
+	if (pdev->vendor == PCI_VENDOR_ID_INTEL &&
+	    (pdev->device == 0x2652 || pdev->device == 0x2653)) {
+		u8 map;
+
+		/* ICH6s share the same PCI ID for both piix and ahci
+		 * modes.  Enabling ahci mode while MAP indicates
+		 * combined mode is a bad idea.  Yield to ata_piix.
+		 */
+		pci_read_config_byte(pdev, ICH_MAP, &map);
+		if (map & 0x3) {
+			dev_printk(KERN_INFO, &pdev->dev, "controller is in "
+				   "combined mode, can't enable AHCI mode\n");
+			return -ENODEV;
+		}
+	}
+
 	hpriv = devm_kzalloc(dev, sizeof(*hpriv), GFP_KERNEL);
 	if (!hpriv)
 		return -ENOMEM;