[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/ata/sata_sil24.c b/drivers/ata/sata_sil24.c
index b0619278454a..26ebffc10f3e 100644
--- a/drivers/ata/sata_sil24.c
+++ b/drivers/ata/sata_sil24.c
@@ -796,16 +796,19 @@ static inline void sil24_fill_sg(struct ata_queued_cmd *qc,
                                  struct sil24_sge *sge)
 {
         struct scatterlist *sg;
+        struct sil24_sge *last_sge = NULL;
 
         ata_for_each_sg(sg, qc) {
                 sge->addr = cpu_to_le64(sg_dma_address(sg));
                 sge->cnt = cpu_to_le32(sg_dma_len(sg));
-                if (ata_sg_is_last(sg, qc))
-                        sge->flags = cpu_to_le32(SGE_TRM);
-                else
-                        sge->flags = 0;
+                sge->flags = 0;
+
+                last_sge = sge;
                 sge++;
         }
+
+        if (likely(last_sge))
+                last_sge->flags = cpu_to_le32(SGE_TRM);
 }
 
 static int sil24_qc_defer(struct ata_queued_cmd *qc)