IB/mlx4: Fix creation of kernel QP with max number of send s/g entries

When creating a kernel QP where the consumer asked for a send queue
with lots of scatter/gater entries, set_kernel_sq_size() incorrectly
returned an error if the send queue stride is larger than the
hardware's maximum send work request descriptor size.  This is not a
problem; the only issue is to make sure that the actual descriptors
used do not overflow the maximum descriptor size, so check this instead.

Clamp the returned max_send_sge value to be no bigger than what
query_device returns for the max_sge to avoid confusing hapless users,
even if the hardware is capable of handling a few more s/g entries.

This bug caused NFS/RDMA mounts to fail when the server adapter used
the mlx4 driver.
Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/hw/mlx4/qp.c

@@ -333,6 +333,9 @@ static int set_kernel_sq_size(struct mlx4_ib_dev *dev, struct ib_qp_cap *cap,
 		cap->max_inline_data + sizeof (struct mlx4_wqe_inline_seg)) +
 		send_wqe_overhead(type, qp->flags);
 
+	if (s > dev->dev->caps.max_sq_desc_sz)
+		return -EINVAL;
+
 	/*
 	 * Hermon supports shrinking WQEs, such that a single work
 	 * request can include multiple units of 1 << wqe_shift.  This
@@ -372,9 +375,6 @@ static int set_kernel_sq_size(struct mlx4_ib_dev *dev, struct ib_qp_cap *cap,
 		qp->sq.wqe_shift = ilog2(roundup_pow_of_two(s));
 
 	for (;;) {
-		if (1 << qp->sq.wqe_shift > dev->dev->caps.max_sq_desc_sz)
-			return -EINVAL;
-
 		qp->sq_max_wqes_per_wr = DIV_ROUND_UP(s, 1U << qp->sq.wqe_shift);
 
 		/*
@@ -395,7 +395,8 @@ static int set_kernel_sq_size(struct mlx4_ib_dev *dev, struct ib_qp_cap *cap,
 		++qp->sq.wqe_shift;
 	}
 
-	qp->sq.max_gs = ((qp->sq_max_wqes_per_wr << qp->sq.wqe_shift) -
+	qp->sq.max_gs = (min(dev->dev->caps.max_sq_desc_sz,
+			     (qp->sq_max_wqes_per_wr << qp->sq.wqe_shift)) -
 			 send_wqe_overhead(type, qp->flags)) /
 		sizeof (struct mlx4_wqe_data_seg);
 
@@ -411,7 +412,9 @@ static int set_kernel_sq_size(struct mlx4_ib_dev *dev, struct ib_qp_cap *cap,
 
 	cap->max_send_wr  = qp->sq.max_post =
 		(qp->sq.wqe_cnt - qp->sq_spare_wqes) / qp->sq_max_wqes_per_wr;
-	cap->max_send_sge = qp->sq.max_gs;
+	cap->max_send_sge = min(qp->sq.max_gs,
+				min(dev->dev->caps.max_sq_sg,
+				    dev->dev->caps.max_rq_sg));
 	/* We don't support inline sends for kernel QPs (yet) */
 	cap->max_inline_data = 0;