s390/qdio: simplify overlap calculation on Input refill

Refilling the Input Queue requires additional checks, as the refilled
SBALs can overlap with the ACKs that qdio maintains on the queue.

This code path is way too complex, and does a whole bunch of wrap-around
checks that the modulo arithmetic in sub_buf() takes care of by itself.
So shrink down all that code into a few lines of equivalent
functionality.
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

drivers/s390/cio/qdio_main.c

@@ -1438,24 +1438,6 @@ int qdio_activate(struct ccw_device *cdev)
 }
 EXPORT_SYMBOL_GPL(qdio_activate);
 
-static inline int buf_in_between(int bufnr, int start, int count)
-{
-	int end = add_buf(start, count);
-
-	if (end > start) {
-		if (bufnr >= start && bufnr < end)
-			return 1;
-		else
-			return 0;
-	}
-
-	/* wrap-around case */
-	if (bufnr >= start || bufnr < end)
-		return 1;
-	else
-		return 0;
-}
-
 /**
  * handle_inbound - reset processed input buffers
  * @q: queue containing the buffers
@@ -1466,36 +1448,18 @@ static inline int buf_in_between(int bufnr, int start, int count)
 static int handle_inbound(struct qdio_q *q, unsigned int callflags,
 			  int bufnr, int count)
 {
-	int diff;
+	int overlap;
 
 	qperf_inc(q, inbound_call);
 
-	if (!q->u.in.ack_count)
-		goto set;
-
-	/* protect against stop polling setting an ACK for an emptied slsb */
-	if (count == QDIO_MAX_BUFFERS_PER_Q) {
-		/* overwriting everything, just delete polling status */
-		q->u.in.ack_count = 0;
-		goto set;
-	} else if (buf_in_between(q->u.in.ack_start, bufnr, count)) {
-		if (is_qebsm(q)) {
-			/* partial overwrite, just update ack_start */
-			diff = add_buf(bufnr, count);
-			diff = sub_buf(diff, q->u.in.ack_start);
-			q->u.in.ack_count -= diff;
-			if (q->u.in.ack_count <= 0) {
-				q->u.in.ack_count = 0;
-				goto set;
-			}
-			q->u.in.ack_start = add_buf(q->u.in.ack_start, diff);
-		} else {
-			/* the only ACK will be deleted */
-			q->u.in.ack_count = 0;
-		}
+	/* If any ACKed SBALs are returned to HW, adjust ACK tracking: */
+	overlap = min(count - sub_buf(q->u.in.ack_start, bufnr),
+		      q->u.in.ack_count);
+	if (overlap > 0) {
+		q->u.in.ack_start = add_buf(q->u.in.ack_start, overlap);
+		q->u.in.ack_count -= overlap;
 	}
 
-set:
 	count = set_buf_states(q, bufnr, SLSB_CU_INPUT_EMPTY, count);
 	atomic_add(count, &q->nr_buf_used);