[PATCH] libata: use FLUSH_EXT only when driver is larger than LBA28 limit

Many drives support LBA48 even when its capacity is smaller than
1<<28, as LBA48 is required for many functionalities.  FLUSH_EXT is
mandatory for drives w/ LBA48 support.

Interestingly, at least one of such drives (ST960812A) has problems
dealing with FLUSH_EXT.  It eventually completes the command but takes
around 7 seconds to finish in many cases thus drastically slowing down
IO transactions.  This seems to be a firmware bug which sneaked into
production probably because no other ATA driver including linux IDE
issues FLUSH_EXT to drives which report support for LBA48 & FLUSH_EXT
but is smaller than 1<<28 blocks.

This patch adds ATA_DFLAG_FLUSH_EXT which is set iff the drive
supports LBA48 & FLUSH_EXT and is larger than LBA28 limit.  Both cache
flush paths are updated to issue FLUSH_EXT only when the flag is set.
Note that the changed behavior is more inline with the rest of libata.
libata prefers shorter commands whenever possible.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Cc: Danny Kukawka <dkukawka@novell.com>
Cc: Stefan Seyfried <seife@novell.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

1 files changed, 1 insertions, 2 deletions

diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index f13dd07a5331..7a55c2e4ea6e 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -1027,8 +1027,7 @@ static unsigned int ata_scsi_flush_xlat(struct ata_queued_cmd *qc, const u8 *scs
         tf->flags |= ATA_TFLAG_DEVICE;
         tf->protocol = ATA_PROT_NODATA;
 
-        if ((qc->dev->flags & ATA_DFLAG_LBA48) &&
-            (ata_id_has_flush_ext(qc->dev->id)))
+        if (qc->dev->flags & ATA_DFLAG_FLUSH_EXT)
                 tf->command = ATA_CMD_FLUSH_EXT;
         else
                 tf->command = ATA_CMD_FLUSH;