s390/qdio: simplify SBAL range calculation

When passing a range of ready-to-process SBALs to the upper-layer
driver, use the available 'count' instead of calculating the distance
between the first_to_check and first_to_kick cursors.

This simplifies the logic of the queue-scan path, and opens up the
possibility of scanning all 128 SBALs in one go (as determining the
reported count no longer requires wrap-around safe arithmetic on the
queue's cursors).

Signed-off-by: Julian Wiedmann <[e-mail]>
Reviewed-by: Jens Remus <[e-mail]>
Signed-off-by: Martin Schwidefsky <[e-mail]>

drivers/s390/cio/qdio_main.c

···
 	return phys_aob;
 }
 
-static void qdio_kick_handler(struct qdio_q *q)
+static void qdio_kick_handler(struct qdio_q *q, unsigned int count)
 {
 	int start = q->first_to_kick;
-	int end = q->first_to_check;
-	int count;
 
 	if (unlikely(q->irq_ptr->state != QDIO_IRQ_STATE_ACTIVE))
 		return;
-
-	count = sub_buf(end, start);
 
 	if (q->is_input_q) {
 		qperf_inc(q, inbound_handler);
···
 		   q->irq_ptr->int_parm);
 
 	/* for the next time */
-	q->first_to_kick = end;
+	q->first_to_kick = add_buf(start, count);
 	q->qdio_error = 0;
 }
 
···
 	if (count == 0)
 		return;
 
-	qdio_kick_handler(q);
+	qdio_kick_handler(q, count);
 
 	if (!qdio_inbound_q_done(q)) {
 		/* means poll time is not yet over */
···
 
 	count = qdio_outbound_q_moved(q);
 	if (count)
-		qdio_kick_handler(q);
+		qdio_kick_handler(q, count);
 
 	if (queue_type(q) == QDIO_ZFCP_QFMT && !pci_out_supported(q->irq_ptr) &&
 	    !qdio_outbound_q_done(q))
···
 	if (count == 0)
 		return;
 
-	qdio_kick_handler(q);
+	qdio_kick_handler(q, count);
 
 	if (!qdio_inbound_q_done(q)) {
 		qperf_inc(q, tasklet_inbound_resched);
···
 			  int *error)
 {
 	struct qdio_q *q;
-	int start, end;
 	struct qdio_irq *irq_ptr = cdev->private->qdio_data;
 	int count;
 
···
 	if (unlikely(q->irq_ptr->state != QDIO_IRQ_STATE_ACTIVE))
 		return -EIO;
 
-	start = q->first_to_kick;
-	end = q->first_to_check;
-	*bufnr = start;
+	*bufnr = q->first_to_kick;
 	*error = q->qdio_error;
 
 	/* for the next time */
-	q->first_to_kick = end;
+	q->first_to_kick = add_buf(q->first_to_kick, count);
 	q->qdio_error = 0;
-	return sub_buf(end, start);
+
+	return count;
 }
 EXPORT_SYMBOL(qdio_get_next_buffers);