[PATCH] ahci: enable prefetching for PACKET commands

[Tejun Heo <htejun@gmail.com>]

Turn on AHCI_CMD_PREFETCH for PACKET commands.  This hints the
controller that it can prefetch the CDB and the PRD entries.  This
patch is originally from Jeff Garzik.

Signed-off-by: Tejun Heo <htejun@gmail.com>

---

Jeff, I'll send two flavors of this patch.  The other one will enable
AHCI_CMD_PREFETCH for both ATA and ATAPI devices.  I've tested both
cases on ICH7R.

 ahci.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/ahci.c b/drivers/scsi/ahci.c
index 00dfdef..e97ab3e 100644
--- a/drivers/scsi/ahci.c
+++ b/drivers/scsi/ahci.c
@@ -66,6 +66,7 @@ enum {
 	AHCI_IRQ_ON_SG		= (1 << 31),
 	AHCI_CMD_ATAPI		= (1 << 5),
 	AHCI_CMD_WRITE		= (1 << 6),
+	AHCI_CMD_PREFETCH	= (1 << 7),
 	AHCI_CMD_RESET		= (1 << 8),
 	AHCI_CMD_CLR_BUSY	= (1 << 10),
 
@@ -631,7 +632,7 @@ static void ahci_qc_prep(struct ata_queu
 	if (qc->tf.flags & ATA_TFLAG_WRITE)
 		opts |= AHCI_CMD_WRITE;
 	if (is_atapi)
-		opts |= AHCI_CMD_ATAPI;
+		opts |= AHCI_CMD_ATAPI | AHCI_CMD_PREFETCH;
 
 	ahci_fill_cmd_slot(pp, opts);
 }
-
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