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

Index: work/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 
 	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;