[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>

3 files changed, 7 insertions, 3 deletions

diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index f531a89c26c9..d94b8a02c340 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -1457,6 +1457,10 @@ int ata_dev_configure(struct ata_device *dev)
                         if (ata_id_has_lba48(id)) {
                                 dev->flags |= ATA_DFLAG_LBA48;
                                 lba_desc = "LBA48";
+
+                                if (dev->n_sectors >= (1UL << 28) &&
+                                    ata_id_has_flush_ext(id))
+                                        dev->flags |= ATA_DFLAG_FLUSH_EXT;
                         }
 
                         /* config NCQ */
@@ -5128,7 +5132,7 @@ int ata_flush_cache(struct ata_device *dev)
         if (!ata_try_flush_cache(dev))
                 return 0;
 
-        if (ata_id_has_flush_ext(dev->id))
+        if (dev->flags & ATA_DFLAG_FLUSH_EXT)
                 cmd = ATA_CMD_FLUSH_EXT;
         else
                 cmd = ATA_CMD_FLUSH;
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;
diff --git a/include/linux/libata.h b/include/linux/libata.h
index 0d0ddeaee73f..36e233cc3886 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -140,6 +140,7 @@ enum {
         ATA_DFLAG_LBA48         = (1 << 1), /* device supports LBA48 */
         ATA_DFLAG_CDB_INTR      = (1 << 2), /* device asserts INTRQ when ready for CDB */
         ATA_DFLAG_NCQ           = (1 << 3), /* device supports NCQ */
+        ATA_DFLAG_FLUSH_EXT     = (1 << 4), /* do FLUSH_EXT instead of FLUSH */
         ATA_DFLAG_CFG_MASK      = (1 << 8) - 1,
 
         ATA_DFLAG_PIO           = (1 << 8), /* device limited to PIO mode */