libata: set dma_mode to 0xff in reset

ata_device->dma_mode's initial value is zero, which is not a valid dma
mode, but ata_dma_enabled will return true for this value. This patch
sets dma_mode to 0xff in reset function, so that ata_dma_enabled will
not return true for this case, or it will cause problem for pata_acpi.

The corrsponding bugzilla page is at:
https://bugzilla.kernel.org/show_bug.cgi?id=49151

Reported-by: Phillip Wood <[email protected]>
Signed-off-by: Aaron Lu <[email protected]>
Tested-by: Szymon Janc <[email protected]>
Tested-by: Dutra Julio <[email protected]>
Acked-by: Alan Cox <[email protected]>
Cc: <[email protected]>
Signed-off-by: Jeff Garzik <[email protected]>

drivers/ata/libata-core.c

@@ -2559,6 +2559,7 @@ int ata_bus_probe(struct ata_port *ap)
 		 * bus as we may be talking too fast.
 		 */
 		dev->pio_mode = XFER_PIO_0;
+		dev->dma_mode = 0xff;
 
 		/* If the controller has a pio mode setup function
 		 * then use it to set the chipset to rights. Don't

drivers/ata/libata-eh.c

@@ -2657,6 +2657,7 @@ int ata_eh_reset(struct ata_link *link, int classify,
 		 * bus as we may be talking too fast.
 		 */
 		dev->pio_mode = XFER_PIO_0;
+		dev->dma_mode = 0xff;
 
 		/* If the controller has a pio mode setup function
 		 * then use it to set the chipset to rights. Don't