[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, 6 insertions, 3 deletions

diff --git a/drivers/ata/pdc_adma.c b/drivers/ata/pdc_adma.c
index 8d1b03d5bcb1..199f7e150eb3 100644
--- a/drivers/ata/pdc_adma.c
+++ b/drivers/ata/pdc_adma.c
@@ -318,7 +318,7 @@ static int adma_fill_sg(struct ata_queued_cmd *qc)
         struct scatterlist *sg;
         struct ata_port *ap = qc->ap;
         struct adma_port_priv *pp = ap->private_data;
-        u8  *buf = pp->pkt;
+        u8  *buf = pp->pkt, *last_buf = NULL;
         int i = (2 + buf[3]) * 8;
         u8 pFLAGS = pORD | ((qc->tf.flags & ATA_TFLAG_WRITE) ? pDIRO : 0);
 
@@ -334,8 +334,7 @@ static int adma_fill_sg(struct ata_queued_cmd *qc)
                 *(__le32 *)(buf + i) = cpu_to_le32(len);
                 i += 4;
 
-                if (ata_sg_is_last(sg, qc))
-                        pFLAGS |= pEND;
+                last_buf = &buf[i];
                 buf[i++] = pFLAGS;
                 buf[i++] = qc->dev->dma_mode & 0xf;
                 buf[i++] = 0;   /* pPKLW */
@@ -348,6 +347,10 @@ static int adma_fill_sg(struct ata_queued_cmd *qc)
                 VPRINTK("PRD[%u] = (0x%lX, 0x%X)\n", i/4,
                                         (unsigned long)addr, len);
         }
+
+        if (likely(last_buf))
+                *last_buf |= pEND;
+
         return i;
 }