IB/mthca: correct log2 calculation

Fix thinko in rd_atomic calculation: ffs(x) - 1 does not find the next
power of 2 -- it should be fls(x - 1).
Signed-off-by: Jack Morgenstein <jackm@mellanox.co.il>
Signed-off-by: Michael S. Tsirkin <mst@mellanox.co.il>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/hw/mthca/mthca_qp.c

@@ -728,9 +728,9 @@ int mthca_modify_qp(struct ib_qp *ibqp, struct ib_qp_attr *attr, int attr_mask)
 	}
 
 	if (attr_mask & IB_QP_MAX_QP_RD_ATOMIC) {
-		qp_context->params1 |= cpu_to_be32(min(attr->max_rd_atomic ?
-						       ffs(attr->max_rd_atomic) - 1 : 0,
-						       7) << 21);
+		if (attr->max_rd_atomic)
+			qp_context->params1 |=
+				cpu_to_be32(fls(attr->max_rd_atomic - 1) << 21);
 		qp_param->opt_param_mask |= cpu_to_be32(MTHCA_QP_OPTPAR_SRA_MAX);
 	}
 
@@ -769,8 +769,6 @@ int mthca_modify_qp(struct ib_qp *ibqp, struct ib_qp_attr *attr, int attr_mask)
 	}
 
 	if (attr_mask & IB_QP_MAX_DEST_RD_ATOMIC) {
-		u8 rra_max;
-
 		if (qp->resp_depth && !attr->max_dest_rd_atomic) {
 			/*
 			 * Lowering our responder resources to zero.
@@ -798,13 +796,10 @@ int mthca_modify_qp(struct ib_qp *ibqp, struct ib_qp_attr *attr, int attr_mask)
 								MTHCA_QP_OPTPAR_RAE);
 		}
 
-		for (rra_max = 0;
-		     1 << rra_max < attr->max_dest_rd_atomic &&
-			     rra_max < dev->qp_table.rdb_shift;
-		     ++rra_max)
-			; /* nothing */
+		if (attr->max_dest_rd_atomic)
+			qp_context->params2 |=
+				cpu_to_be32(fls(attr->max_dest_rd_atomic - 1) << 21);
 
-		qp_context->params2      |= cpu_to_be32(rra_max << 21);
 		qp_param->opt_param_mask |= cpu_to_be32(MTHCA_QP_OPTPAR_RRA_MAX);
 
 		qp->resp_depth = attr->max_dest_rd_atomic;