[openib-general] [PATCH][2/3] IPoIB: fix static rate calculation

[Roland Dreier]

Correct and simplify calculation of static rate.  We need to round up
the quotient of (local_rate - path_rate) / path_rate.  To round up we
add (path_rate - 1) to the numerator, so the quotient simplifies to
(local_rate - 1) / path_rate.

No idea how I came up with the old formula.

Signed-off-by: Roland Dreier <roland at topspin.com>

--- linux-export.orig/drivers/infiniband/ulp/ipoib/ipoib_main.c	2005-03-31 19:06:47.984714505 -0800
+++ linux-export/drivers/infiniband/ulp/ipoib/ipoib_main.c	2005-03-31 19:26:39.094134171 -0800
@@ -302,11 +302,10 @@
 			.sl 	       = pathrec->sl,
 			.port_num      = priv->port
 		};
+		int path_rate = ib_sa_rate_enum_to_int(pathrec->rate);
 
-		if (ib_sa_rate_enum_to_int(pathrec->rate) > 0)
-			av.static_rate = (2 * priv->local_rate -
-					  ib_sa_rate_enum_to_int(pathrec->rate) - 1) /
-				(priv->local_rate ? priv->local_rate : 1);
+		if (path_rate > 0 && priv->local_rate > path_rate)
+			av.static_rate = (priv->local_rate - 1) / path_rate;
 
 		ipoib_dbg(priv, "static_rate %d for local port %dX, path %dX\n",
 			  av.static_rate, priv->local_rate,
--- linux-export.orig/drivers/infiniband/ulp/ipoib/ipoib_multicast.c	2005-03-31 19:07:01.877698296 -0800
+++ linux-export/drivers/infiniband/ulp/ipoib/ipoib_multicast.c	2005-03-31 19:26:03.861782487 -0800
@@ -258,13 +258,12 @@
 				.traffic_class = mcast->mcmember.traffic_class
 			}
 		};
+		int path_rate = ib_sa_rate_enum_to_int(mcast->mcmember.rate);
 
 		av.grh.dgid = mcast->mcmember.mgid;
 
-		if (ib_sa_rate_enum_to_int(mcast->mcmember.rate) > 0)
-			av.static_rate = (2 * priv->local_rate -
-					  ib_sa_rate_enum_to_int(mcast->mcmember.rate) - 1) /
-				(priv->local_rate ? priv->local_rate : 1);
+		if (path_rate > 0 && priv->local_rate > path_rate)
+			av.static_rate = (priv->local_rate - 1) / path_rate;
 
 		ipoib_dbg_mcast(priv, "static_rate %d for local port %dX, mcmember %dX\n",
 				av.static_rate, priv->local_rate,