[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>
diff --git a/drivers/ata/pdc_adma.c b/drivers/ata/pdc_adma.c
index 8d1b03d..199f7e1 100644
--- a/drivers/ata/pdc_adma.c
+++ b/drivers/ata/pdc_adma.c
@@ -318,7 +318,7 @@
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 @@
*(__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 @@
VPRINTK("PRD[%u] = (0x%lX, 0x%X)\n", i/4,
(unsigned long)addr, len);
}
+
+ if (likely(last_buf))
+ *last_buf |= pEND;
+
return i;
}