[libata] ahci: SB600 workaround is suspect... play it safe for now

At least one report claims that a878539e
failed to solve lockups, whereas the old limit-to-32-bit trick worked.

Restore the 32-bit limit, but also leave the 255-sector limit in place,
because we know that's needed as well.
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/ata/ahci.c

@@ -433,6 +433,7 @@ static const struct ata_port_info ahci_port_info[] = {
 	/* board_ahci_sb600 */
 	{
 		AHCI_HFLAGS	(AHCI_HFLAG_IGN_SERR_INTERNAL |
+				 AHCI_HFLAG_32BIT_ONLY |
 				 AHCI_HFLAG_SECT255 | AHCI_HFLAG_NO_PMP),
 		.flags		= AHCI_FLAG_COMMON,
 		.link_flags	= AHCI_LFLAG_COMMON,
@@ -1217,8 +1218,11 @@ static void ahci_dev_config(struct ata_device *dev)
 {
 	struct ahci_host_priv *hpriv = dev->link->ap->host->private_data;
 
-	if (hpriv->flags & AHCI_HFLAG_SECT255)
+	if (hpriv->flags & AHCI_HFLAG_SECT255) {
 		dev->max_sectors = 255;
+		ata_dev_printk(dev, KERN_INFO,
+			       "SB600 AHCI: limiting to 255 sectors per cmd\n");
+	}
 }
 
 static unsigned int ahci_dev_classify(struct ata_port *ap)