[PATCH V3 10/15] scsi: aha152x: use sg helper to operate scatterlist

[Ming Lei <ming.lei@redhat.com>]

Use the scatterlist iterators and remove direct indexing of the
scatterlist array.

This way allows us to pre-allocate one small scatterlist, which can be
chained with one runtime allocated scatterlist if the pre-allocated one
isn't enough for the whole request.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 drivers/scsi/aha152x.c | 29 +++++++++++++++++++----------
 1 file changed, 19 insertions(+), 10 deletions(-)

diff --git a/drivers/scsi/aha152x.c b/drivers/scsi/aha152x.c
index 97872838b983..bc9d12aa7880 100644
--- a/drivers/scsi/aha152x.c
+++ b/drivers/scsi/aha152x.c
@@ -2033,7 +2033,7 @@ static void datai_run(struct Scsi_Host *shpnt)
 				    CURRENT_SC->SCp.buffers_residual > 0) {
 					/* advance to next buffer */
 					CURRENT_SC->SCp.buffers_residual--;
-					CURRENT_SC->SCp.buffer++;
+					CURRENT_SC->SCp.buffer = sg_next(CURRENT_SC->SCp.buffer);
 					CURRENT_SC->SCp.ptr           = SG_ADDRESS(CURRENT_SC->SCp.buffer);
 					CURRENT_SC->SCp.this_residual = CURRENT_SC->SCp.buffer->length;
 				}
@@ -2139,7 +2139,7 @@ static void datao_run(struct Scsi_Host *shpnt)
 		if(CURRENT_SC->SCp.this_residual==0 && CURRENT_SC->SCp.buffers_residual>0) {
 			/* advance to next buffer */
 			CURRENT_SC->SCp.buffers_residual--;
-			CURRENT_SC->SCp.buffer++;
+			CURRENT_SC->SCp.buffer = sg_next(CURRENT_SC->SCp.buffer);
 			CURRENT_SC->SCp.ptr           = SG_ADDRESS(CURRENT_SC->SCp.buffer);
 			CURRENT_SC->SCp.this_residual = CURRENT_SC->SCp.buffer->length;
 		}
@@ -2160,20 +2160,29 @@ static void datao_end(struct Scsi_Host *shpnt)
 	if(TESTLO(DMASTAT, DFIFOEMP)) {
 		int data_count = (DATA_LEN - scsi_get_resid(CURRENT_SC)) -
 			GETSTCNT();
+		struct scatterlist *sg = scsi_sglist(CURRENT_SC);
+		int left, i = 0;
 
 		CMD_INC_RESID(CURRENT_SC, data_count);
 
 		data_count -= CURRENT_SC->SCp.ptr -
 			SG_ADDRESS(CURRENT_SC->SCp.buffer);
-		while(data_count>0) {
-			CURRENT_SC->SCp.buffer--;
-			CURRENT_SC->SCp.buffers_residual++;
-			data_count -= CURRENT_SC->SCp.buffer->length;
+
+		left = CURRENT_SC->transfersize - data_count;
+		for (i = 0; left > 0 && !sg_is_last(sg); i++, sg = sg_next(sg)) {
+			if (left < sg->length)
+				break;
+			left -= sg->length;
+		}
+
+		if (data_count > 0) {
+			CURRENT_SC->SCp.buffers_residual += i;
+			CURRENT_SC->SCp.buffer = sg;
+
+			CURRENT_SC->SCp.ptr = SG_ADDRESS(CURRENT_SC->SCp.buffer) + left;
+			CURRENT_SC->SCp.this_residual = CURRENT_SC->SCp.buffer->length -
+				left;
 		}
-		CURRENT_SC->SCp.ptr = SG_ADDRESS(CURRENT_SC->SCp.buffer) -
-			data_count;
-		CURRENT_SC->SCp.this_residual = CURRENT_SC->SCp.buffer->length +
-			data_count;
 	}
 
 	SETPORT(SXFRCTL0, CH1|CLRCH1|CLRSTCNT);
-- 
2.20.1