"mlx4_en: Enabling new steering" brokenness

[Roland Dreier <roland-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>]

Hi Yevgeny!

So I have a system with an mlx4_en device with pretty old FW (version
2.7.700), old enough that the firmware doesn't have the capability
MLX4_DEV_CAP_FLAG_VEP_UC_STEER set.  And it looks like mlx4_en is
completely broken in this case, at least since your commit
1679200f91da ("mlx4_en: Enabling new steering").  If I try to bring up
the interface, I just see:

    mlx4_en: eth1: Failed to allocate RSS indirection QP

And this is failing because the QPN in 0.

The problem is in drivers/net/mlx4/port.c:mlx4_register_mac():

	if (!(dev->caps.flags & MLX4_DEV_CAP_FLAG_VEP_UC_STEER))
		*qpn = info->base_qpn + free;

but absolutely nothing ever initializes info->base_qpn.  It looks like
the intention of the code is to initialize this in
mlx4_init_port_info(); however even the below hack doesn't seem to fix
things completely -- I still seem to have problems on the RX side
unless I enable promiscuous mode by running tcpdump:

diff --git a/drivers/net/mlx4/main.c b/drivers/net/mlx4/main.c
index c94b342..38092c7 100644
--- a/drivers/net/mlx4/main.c
+++ b/drivers/net/mlx4/main.c
@@ -1125,6 +1125,13 @@ static int mlx4_init_port_info(struct mlx4_dev *dev, int port)
 	info->port_attr.store     = set_port_type;
 	sysfs_attr_init(&info->port_attr.attr);
 
+	err = mlx4_qp_reserve_range(dev, 1, 1, &info->base_qpn);
+	if (err) {
+		mlx4_err(dev, "Failed to reserve QP range for port %d\n", port);
+		info->port = -1;
+		return err;
+	}
+
 	err = device_create_file(&dev->pdev->dev, &info->port_attr);
 	if (err) {
 		mlx4_err(dev, "Failed to create file for port %d\n", port);

Could you take a look at getting this working?  (Or update the driver
so it immediately fails with an informative message if you want to
rely on certain FW versions; and then strip out the old broken
compatibility code)

Thanks!
  Roland
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