[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>
diff --git a/drivers/ata/sata_svw.c b/drivers/ata/sata_svw.c
index 16aa683..fb13b82 100644
--- a/drivers/ata/sata_svw.c
+++ b/drivers/ata/sata_svw.c
@@ -253,21 +253,29 @@
/* 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);
}