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    Subject[PATCH] ahci: enable prefetching for PACKET commands
    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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