scsi: libsas: fix ata xfer length

BugLink: http://bugs.launchpad.net/bugs/1681862

commit 9702c67c upstream.

The total ata xfer length may not be calculated properly, in that we do
not use the proper method to get an sg element dma length.

According to the code comment, sg_dma_len() should be used after
dma_map_sg() is called.

This issue was found by turning on the SMMUv3 in front of the hisi_sas
controller in hip07. Multiple sg elements were being combined into a
single element, but the original first element length was being use as
the total xfer length.

Fixes: ff2aeb1e ("libata: convert to chained sg")
Signed-off-by: John Garry <john.garry@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

drivers/scsi/libsas/sas_ata.c

@@ -218,7 +218,7 @@ static unsigned int sas_ata_qc_issue(struct ata_queued_cmd *qc)
 		task->num_scatter = qc->n_elem;
 	} else {
 		for_each_sg(qc->sg, sg, qc->n_elem, si)
-			xfer += sg->length;
+			xfer += sg_dma_len(sg);
 
 		task->total_xfer_len = xfer;
 		task->num_scatter = si;