ntb_transport: fix bug calculating num_qps_mw

commit 8e8496e0e9564b66165f5219a4e8ed20b0d3fc6b upstream.

A divide by zero error occurs if qp_count is less than mw_count because
num_qps_mw is calculated to be zero. The calculation appears to be
incorrect.

The requirement is for num_qps_mw to be set to qp_count / mw_count
with any remainder divided among the earlier mws.

For example, if mw_count is 5 and qp_count is 12 then mws 0 and 1
will have 3 qps per window and mws 2 through 4 will have 2 qps per window.
Thus, when mw_num < qp_count % mw_count, num_qps_mw is 1 higher
than when mw_num >= qp_count.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Fixes: e26a584 ("NTB: Split ntb_hw_intel and ntb_transport drivers")
Acked-by: Allen Hubbe <Allen.Hubbe@dell.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: lsgunth

drivers/ntb/ntb_transport.c

@@ -599,7 +599,7 @@ static int ntb_transport_setup_qp_mw(struct ntb_transport_ctx *nt,
 	if (!mw->virt_addr)
 		return -ENOMEM;
 
-	if (qp_count % mw_count && mw_num + 1 < qp_count / mw_count)
+	if (mw_num < qp_count % mw_count)
 		num_qps_mw = qp_count / mw_count + 1;
 	else
 		num_qps_mw = qp_count / mw_count;
@@ -947,7 +947,7 @@ static int ntb_transport_init_queue(struct ntb_transport_ctx *nt,
 	qp->event_handler = NULL;
 	ntb_qp_link_down_reset(qp);
 
-	if (qp_count % mw_count && mw_num + 1 < qp_count / mw_count)
+	if (mw_num < qp_count % mw_count)
 		num_qps_mw = qp_count / mw_count + 1;
 	else
 		num_qps_mw = qp_count / mw_count;