[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, 5 insertions, 1 deletions

diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index f531a89c26c..d94b8a02c34 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;