[PATCH] libata: make ata_sg_setup_one() trim zero length sg
This patch makes ata_sg_setup_one() trim sg entry (thus making
qc->n_elem zero) if padding results in zero length sg entry.
Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>
diff --git a/drivers/scsi/libata-core.c b/drivers/scsi/libata-core.c
index bbac87a..5f1d758 100644
--- a/drivers/scsi/libata-core.c
+++ b/drivers/scsi/libata-core.c
@@ -2514,7 +2514,7 @@
assert(sg != NULL);
if (qc->flags & ATA_QCFLAG_SINGLE)
- assert(qc->n_elem == 1);
+ assert(qc->n_elem <= 1);
VPRINTK("unmapping %u sg elements\n", qc->n_elem);
@@ -2537,7 +2537,7 @@
kunmap_atomic(addr, KM_IRQ0);
}
} else {
- if (sg_dma_len(&sg[0]) > 0)
+ if (qc->n_elem)
dma_unmap_single(ap->host_set->dev,
sg_dma_address(&sg[0]), sg_dma_len(&sg[0]),
dir);
@@ -2715,6 +2715,7 @@
int dir = qc->dma_dir;
struct scatterlist *sg = qc->__sg;
dma_addr_t dma_address;
+ int trim_sg = 0;
/* we must lengthen transfers to end on a 32-bit boundary */
qc->pad_len = sg->length & 3;
@@ -2734,13 +2735,15 @@
sg_dma_len(psg) = ATA_DMA_PAD_SZ;
/* trim sg */
sg->length -= qc->pad_len;
+ if (sg->length == 0)
+ trim_sg = 1;
DPRINTK("padding done, sg->length=%u pad_len=%u\n",
sg->length, qc->pad_len);
}
- if (!sg->length) {
- sg_dma_address(sg) = 0;
+ if (trim_sg) {
+ qc->n_elem--;
goto skip_map;
}
@@ -2753,9 +2756,9 @@
}
sg_dma_address(sg) = dma_address;
-skip_map:
sg_dma_len(sg) = sg->length;
+skip_map:
DPRINTK("mapped buffer of %d bytes for %s\n", sg_dma_len(sg),
qc->tf.flags & ATA_TFLAG_WRITE ? "write" : "read");