ahci: disable 64bit dma on sb600

SB600 claims it can do 64bit DMA but it can't.  Disable it.
Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

drivers/ata/ahci.c

@@ -170,6 +170,7 @@ enum {
 	AHCI_FLAG_IGN_IRQ_IF_ERR	= (1 << 25), /* ignore IRQ_IF_ERR */
 	AHCI_FLAG_HONOR_PI		= (1 << 26), /* honor PORTS_IMPL */
 	AHCI_FLAG_IGN_SERR_INTERNAL	= (1 << 27), /* ignore SERR_INTERNAL */
+	AHCI_FLAG_32BIT_ONLY		= (1 << 28), /* force 32bit */
 
 	AHCI_FLAG_COMMON		= ATA_FLAG_SATA | ATA_FLAG_NO_LEGACY |
 					  ATA_FLAG_MMIO | ATA_FLAG_PIO_DMA |
@@ -354,7 +355,8 @@ static const struct ata_port_info ahci_port_info[] = {
 	/* board_ahci_sb600 */
 	{
 		.flags		= AHCI_FLAG_COMMON |
-				  AHCI_FLAG_IGN_SERR_INTERNAL,
+				  AHCI_FLAG_IGN_SERR_INTERNAL |
+				  AHCI_FLAG_32BIT_ONLY,
 		.pio_mask	= 0x1f, /* pio0-4 */
 		.udma_mask	= 0x7f, /* udma0-6 ; FIXME */
 		.port_ops	= &ahci_ops,
@@ -492,6 +494,13 @@ static void ahci_save_initial_config(struct pci_dev *pdev,
 	hpriv->saved_cap = cap = readl(mmio + HOST_CAP);
 	hpriv->saved_port_map = port_map = readl(mmio + HOST_PORTS_IMPL);
 
+	/* some chips lie about 64bit support */
+	if ((cap & HOST_CAP_64) && (pi->flags & AHCI_FLAG_32BIT_ONLY)) {
+		dev_printk(KERN_INFO, &pdev->dev,
+			   "controller can't do 64bit DMA, forcing 32bit\n");
+		cap &= ~HOST_CAP_64;
+	}
+
 	/* fixup zero port_map */
 	if (!port_map) {
 		port_map = (1 << ahci_nr_ports(hpriv->cap)) - 1;