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

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

1 files changed, 5 insertions, 1 deletions

diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index dce65651d858..ad8e2c64c867 100644
--- a/drivers/ata/libata-core.c
+++ b/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