IB/mlx4: Make sure RQ allocation is always valid

QPs attached to an SRQ must never have their own RQ, and QPs not
attached to SRQs must have an RQ with at least 1 entry.  Enforce all
of this in set_rq_size().

Based on a patch by Eli Cohen <eli@mellanox.co.il>.
Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/hw/mlx4/qp.c

@@ -189,18 +189,28 @@ static int send_wqe_overhead(enum ib_qp_type type)
 }
 
 static int set_rq_size(struct mlx4_ib_dev *dev, struct ib_qp_cap *cap,
-		       struct mlx4_ib_qp *qp)
+		       int is_user, int has_srq, struct mlx4_ib_qp *qp)
 {
 	/* Sanity check RQ size before proceeding */
 	if (cap->max_recv_wr  > dev->dev->caps.max_wqes  ||
 	    cap->max_recv_sge > dev->dev->caps.max_rq_sg)
 		return -EINVAL;
 
-	qp->rq.max = cap->max_recv_wr ? roundup_pow_of_two(cap->max_recv_wr) : 0;
+	if (has_srq) {
+		/* QPs attached to an SRQ should have no RQ */
+		if (cap->max_recv_wr)
+			return -EINVAL;
 
-	qp->rq.wqe_shift = ilog2(roundup_pow_of_two(cap->max_recv_sge *
-						    sizeof (struct mlx4_wqe_data_seg)));
-	qp->rq.max_gs    = (1 << qp->rq.wqe_shift) / sizeof (struct mlx4_wqe_data_seg);
+		qp->rq.max = qp->rq.max_gs = 0;
+	} else {
+		/* HW requires >= 1 RQ entry with >= 1 gather entry */
+		if (is_user && (!cap->max_recv_wr || !cap->max_recv_sge))
+			return -EINVAL;
+
+		qp->rq.max	 = roundup_pow_of_two(max(1, cap->max_recv_wr));
+		qp->rq.max_gs	 = roundup_pow_of_two(max(1, cap->max_recv_sge));
+		qp->rq.wqe_shift = ilog2(qp->rq.max_gs * sizeof (struct mlx4_wqe_data_seg));
+	}
 
 	cap->max_recv_wr  = qp->rq.max;
 	cap->max_recv_sge = qp->rq.max_gs;
@@ -285,7 +295,7 @@ static int create_qp_common(struct mlx4_ib_dev *dev, struct ib_pd *pd,
 	qp->sq.head	    = 0;
 	qp->sq.tail	    = 0;
 
-	err = set_rq_size(dev, &init_attr->cap, qp);
+	err = set_rq_size(dev, &init_attr->cap, !!pd->uobject, !!init_attr->srq, qp);
 	if (err)
 		goto err;