s390/qdio: allow to scan all Output SBALs in one go

Old code restricted the number of inspected SBALs to
QDIO_MAX_BUFFERS_PER_Q - 1, as otherwise the first_to_check and
first_to_kick cursors could overlap. Subsequent code would then assume that
there was no progress on the queue, when in fact _all_ SBALs on the queue
were ready-to-process.

This limitation no longer applies, so allow the queue-scan code to inspect
all SBALs on the queue. Note that qeth requires an additional patch
("s390/qeth: stop/wake TX queues based on their fill level"), to avoid
potential queue stalls when all 128 SBALs are reported as ready-to-process.

Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

drivers/s390/cio/qdio_main.c

@@ -719,11 +719,7 @@ static int get_outbound_buffer_frontier(struct qdio_q *q, unsigned int start)
 		    multicast_outbound(q)))
 			qdio_siga_sync_q(q);
 
-	/*
-	 * Don't check 128 buffers, as otherwise qdio_inbound_q_moved
-	 * would return 0.
-	 */
-	count = min(atomic_read(&q->nr_buf_used), QDIO_MAX_BUFFERS_MASK);
+	count = atomic_read(&q->nr_buf_used);
 	if (!count)
 		return 0;