IB/mlx4: Eliminate duplicate barriers on weakly-ordered archs

Code includes wmb() followed by writel(). writel() already has a barrier on
some architectures like arm64.

This ends up CPU observing two barriers back to back before executing the
register write.

Since code already has an explicit barrier call, changing writel() to
writel_relaxed().

Signed-off-by: Sinan Kaya <okaya@codeaurora.org>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

diff --git a/drivers/infiniband/hw/mlx4/qp.c b/drivers/infiniband/hw/mlx4/qp.c
index 04efc05..523028e 100644 (file)
--- a/drivers/infiniband/hw/mlx4/qp.c
+++ b/drivers/infiniband/hw/mlx4/qp.c
@@ -3894,8 +3894,8 @@ out:
                 */
                wmb();
 
-               writel(qp->doorbell_qpn,
-                      to_mdev(ibqp->device)->uar_map + MLX4_SEND_DOORBELL);
+               writel_relaxed(qp->doorbell_qpn,
+                       to_mdev(ibqp->device)->uar_map + MLX4_SEND_DOORBELL);
 
                /*
                 * Make sure doorbells don't leak out of SQ spinlock