[PATCH] libata: Don't believe bogus claims in the older PIO mode register

Signed-off-by: NAlan Cox <alan@redhat.com>
Signed-off-by: NJeff Garzik <jeff@garzik.org>

drivers/ata/libata-core.c

@@ -870,7 +870,11 @@ static unsigned int ata_id_xfermask(const u16 *id)
 		 * the PIO timing number for the maximum. Turn it into
 		 * a mask.
 		 */
-		pio_mask = (2 << (id[ATA_ID_OLD_PIO_MODES] & 0xFF)) - 1 ;
+		u8 mode = id[ATA_ID_OLD_PIO_MODES] & 0xFF;
+		if (mode < 5)	/* Valid PIO range */
+                	pio_mask = (2 << mode) - 1;
+		else
+			pio_mask = 1;
 
 		/* But wait.. there's more. Design your standards by
 		 * committee and you too can get a free iordy field to