ata_piix.c: check PCI sub-class code before AHCI disabling

@@ -38,6 +38,7 @@ enum {
        PIIX_IOCFG              = 0x54, /* IDE I/O configuration register */
        ICH5_PMR                = 0x90, /* port mapping register */
        ICH5_PCS                = 0x92, /* port control and status */
+       PIIX_SCC                = 0x0A, /* sub-class code register */
 
        PIIX_FLAG_AHCI          = (1 << 28), /* AHCI possible */
        PIIX_FLAG_CHECKINTR     = (1 << 29), /* make sure PCI INTx enabled */

@@ -61,6 +62,8 @@ enum {
        ich6_sata               = 3,
        ich6_sata_rm            = 4,
        ich7_sata               = 5,
+
+       PIIX_AHCI_DEVICE        = 6,
 };
 
 static int piix_init_one (struct pci_dev *pdev,

@@ -609,9 +612,13 @@ static int piix_init_one (struct pci_dev
        port_info[1] = NULL;
 
        if (port_info[0]->host_flags & PIIX_FLAG_AHCI) {
-               int rc = piix_disable_ahci(pdev);
-               if (rc)
-                       return rc;
+               u8 tmp;
+               pci_read_config_byte(pdev, PIIX_SCC, &tmp);
+               if (tmp == PIIX_AHCI_DEVICE) {
+                       int rc = piix_disable_ahci(pdev);
+                       if (rc)
+                           return rc;
+               }
        }
 
        if (port_info[0]->host_flags & PIIX_FLAG_COMBINED) {