[libata] sata_svw: update code comments relating to data corruption

Signed-off-by: Pavel Machek <pavel@suse.cz>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

1 files changed, 23 insertions, 15 deletions

diff --git a/drivers/ata/sata_svw.c b/drivers/ata/sata_svw.c
index 16aa6839aa5..fb13b82aacb 100644
--- a/drivers/ata/sata_svw.c
+++ b/drivers/ata/sata_svw.c
@@ -253,21 +253,29 @@ static void k2_bmdma_start_mmio(struct ata_queued_cmd *qc)
         /* start host DMA transaction */
         dmactl = readb(mmio + ATA_DMA_CMD);
         writeb(dmactl | ATA_DMA_START, mmio + ATA_DMA_CMD);
-        /* There is a race condition in certain SATA controllers that can
-           be seen when the r/w command is given to the controller before the
-           host DMA is started. On a Read command, the controller would initiate
-           the command to the drive even before it sees the DMA start. When there
-           are very fast drives connected to the controller, or when the data request
-           hits in the drive cache, there is the possibility that the drive returns a part
-           or all of the requested data to the controller before the DMA start is issued.
-           In this case, the controller would become confused as to what to do with the data.
-           In the worst case when all the data is returned back to the controller, the
-           controller could hang. In other cases it could return partial data returning
-           in data corruption. This problem has been seen in PPC systems and can also appear
-           on an system with very fast disks, where the SATA controller is sitting behind a
-           number of bridges, and hence there is significant latency between the r/w command
-           and the start command. */
-        /* issue r/w command if the access is to ATA*/
+        /* This works around possible data corruption.
+
+           On certain SATA controllers that can be seen when the r/w
+           command is given to the controller before the host DMA is
+           started.
+
+           On a Read command, the controller would initiate the
+           command to the drive even before it sees the DMA
+           start. When there are very fast drives connected to the
+           controller, or when the data request hits in the drive
+           cache, there is the possibility that the drive returns a
+           part or all of the requested data to the controller before
+           the DMA start is issued.  In this case, the controller
+           would become confused as to what to do with the data.  In
+           the worst case when all the data is returned back to the
+           controller, the controller could hang. In other cases it
+           could return partial data returning in data
+           corruption. This problem has been seen in PPC systems and
+           can also appear on an system with very fast disks, where
+           the SATA controller is sitting behind a number of bridges,
+           and hence there is significant latency between the r/w
+           command and the start command. */
+        /* issue r/w command if the access is to ATA */
         if (qc->tf.protocol == ATA_PROT_DMA)
                 ap->ops->sff_exec_command(ap, &qc->tf);
 }