[libata] kill ata_sg_is_last()

Short term, this works around a bug introduced by early sg-chaining
work.

Long term, removing this function eliminates a branch from a hot
path loop in each scatter/gather table build.  Also, as this code
demonstrates, we don't need to _track_ the end of the s/g list, as
long as we mark it in some way.  And doing so programatically is nice.
So its a useful cleanup, regardless of its short term effects.

Based conceptually on a quick patch by Jens Axboe.

Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

1 files changed, 7 insertions, 4 deletions

diff --git a/drivers/scsi/ipr.c b/drivers/scsi/ipr.c
index b41dfb539021..c316a0bcae6c 100644
--- a/drivers/scsi/ipr.c
+++ b/drivers/scsi/ipr.c
@@ -5134,6 +5134,7 @@ static void ipr_build_ata_ioadl(struct ipr_cmnd *ipr_cmd,
         u32 ioadl_flags = 0;
         struct ipr_ioarcb *ioarcb = &ipr_cmd->ioarcb;
         struct ipr_ioadl_desc *ioadl = ipr_cmd->ioadl;
+        struct ipr_ioadl_desc *last_ioadl = NULL;
         int len = qc->nbytes + qc->pad_len;
         struct scatterlist *sg;
 
@@ -5156,11 +5157,13 @@ static void ipr_build_ata_ioadl(struct ipr_cmnd *ipr_cmd,
         ata_for_each_sg(sg, qc) {
                 ioadl->flags_and_data_len = cpu_to_be32(ioadl_flags | sg_dma_len(sg));
                 ioadl->address = cpu_to_be32(sg_dma_address(sg));
-                if (ata_sg_is_last(sg, qc))
-                        ioadl->flags_and_data_len |= cpu_to_be32(IPR_IOADL_FLAGS_LAST);
-                else
-                        ioadl++;
+
+                last_ioadl = ioadl;
+                ioadl++;
         }
+
+        if (likely(last_ioadl))
+                last_ioadl->flags_and_data_len |= cpu_to_be32(IPR_IOADL_FLAGS_LAST);
 }
 
 /**