[PATCH net-next v3] net/mlx5e: advertise tcp-data-split support

[Dimitri Daskalakis <dimitri.daskalakis1@gmail.com>]

From: Dimitri Daskalakis <daskald@meta.com>

The ability to set tcp-data-split was introduced in
commit 46bcce5dfd33 ("net/mlx5e: Support ethtool tcp-data-split settings")
This commit dropped reporting from mlx5e_ethtool_get_ringparam()
without explaining why. commit d347b28c492e ("net/mlx5e: Add hds-thresh
query support via ethtool") added support for ETHTOOL_RING_USE_HDS_THRS,
and modified mlx5e_ethtool_get_ringparam() to report an hds_thresh of 0.

Between these two commits, the hds selftest helper _defer_reset_hds()
would skip the reset because neither hds-thresh or tcp-data-split was
present in the ring config. After the second commit this introduced
a KeyError in the hds.set_hds_enable/disable tests.

mlx5 couples tcp-data-split with rx-gro-hw. Users can currently disable
tcp-data-split then enable HW GRO. The kernel reports tcp-data-split
off, but the HW is presumably splitting.

Add back tcp-data-split reporting in mlx5e_ethtool_get_ringparam(),
and de-feature tcp-data-split disable. Users can either enable it
(if HW GRO is enabled), or leave it under driver control.

Additionally, move the call to netdev_update_features() out of
mlx5e_ethtool_set_tcp_data_split(). If mlx5e_ethtool_set_ringparam()
fails, this can cause the driver/kernel feature to de-sync.

This is not a fix since HDS/tcp-data-split is still functional with HW
GRO enabled.

Signed-off-by: Dimitri Daskalakis <daskald@meta.com>
---
Changes in v3:
- Drop redundant hw_features check in mlx5e_ethtool_get_ringparam(). Packet
  merge type can only be MLX5E_PACKET_MERGE_SHAMPO when HW GRO is active.
- Address Bjorn's feedback, and drop premature netdev_update_features() call
  in mlx5e_ethtool_set_tcp_data_split()
- Link to v2: https://lore.kernel.org/all/20261006225925.568263-1-dimitri.daskalakis1@gmail.com/
Changes in v2:
- Leave kernel_param->tcp_data_split as ETHTOOL_TCP_DATA_SPLIT_UNKNOWN if the
  device does not support HW GRO
- Prevent users from disabling tcp-data-split
- Link to v1: https://lore.kernel.org/all/20260923230521.1267511-1-dimitri.daskalakis1@gmail.com/

hds.py before:
 # Interface: eth0, driver: mlx5_core
 TAP version 13
 1..13
 ok 1 hds.get_hds # SKIP tcp-data-split not supported by device
 ok 2 hds.get_hds_thresh
 # Exception while handling defer / cleanup (callback 1 of 1)! ...
 # Defer Exception| KeyError: 'tcp-data-split'
 # Defer Exception|
 not ok 3 hds.set_hds_disable
 # Exception while handling defer / cleanup (callback 1 of 1)!
 ...
 # Defer Exception| KeyError: 'tcp-data-split'
 # Defer Exception|
 not ok 4 hds.set_hds_enable
 ok 5 hds.set_hds_thresh_random # SKIP hds-thresh-max is too small
 ok 6 hds.set_hds_thresh_zero
 ok 7 hds.set_hds_thresh_max
 ok 8 hds.set_hds_thresh_gt
 ok 9 hds.set_xdp # SKIP tcp-data-split not supported by device
 ok 10 hds.enabled_set_xdp # SKIP tcp-data-split not supported by device
 ok 11 hds.ioctl # SKIP tcp-data-split not supported by device
 ok 12 hds.ioctl_set_xdp # SKIP tcp-data-split not supported by device
 ok 13 hds.ioctl_enabled_set_xdp # SKIP tcp-data-split not supported by device

hds.py after:
 # Interface: eth0, driver: mlx5_core
 TAP version 13
 1..13
 ok 1 hds.get_hds # SKIP tcp-data-split not supported by device
 ok 2 hds.get_hds_thresh
 ok 3 hds.set_hds_disable # SKIP disabling of HDS not supported by the device
 ok 4 hds.set_hds_enable # SKIP disabling of HDS not supported by the device
 ok 5 hds.set_hds_thresh_random # SKIP hds-thresh-max is too small
 ok 6 hds.set_hds_thresh_zero
 ok 7 hds.set_hds_thresh_max
 ok 8 hds.set_hds_thresh_gt
 ok 9 hds.set_xdp # SKIP tcp-data-split not supported by device
 ok 10 hds.enabled_set_xdp # SKIP tcp-data-split not supported by device
 ok 11 hds.ioctl # SKIP tcp-data-split not supported by device
 ok 12 hds.ioctl_set_xdp # SKIP tcp-data-split not supported by device
 ok 13 hds.ioctl_enabled_set_xdp # SKIP tcp-data-split not supported by device
 # Totals: pass:4 fail:0 xfail:0 xpass:0 skip:9 error:0
---
 .../ethernet/mellanox/mlx5/core/en_ethtool.c  | 23 +++++++++++++++----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_ethtool.c b/drivers/net/ethernet/mellanox/mlx5/core/en_ethtool.c
index 261c466a4d36..c30d751cac2f 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_ethtool.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_ethtool.c
@@ -378,6 +378,9 @@ void mlx5e_ethtool_get_ringparam(struct mlx5e_priv *priv,
 
 	kernel_param->hds_thresh = 0;
 	kernel_param->hds_thresh_max = 0;
+
+	if (priv->channels.params.packet_merge.type == MLX5E_PACKET_MERGE_SHAMPO)
+		kernel_param->tcp_data_split = ETHTOOL_TCP_DATA_SPLIT_ENABLED;
 }
 
 static void mlx5e_get_ringparam(struct net_device *dev,
@@ -403,10 +406,11 @@ static bool mlx5e_ethtool_set_tcp_data_split(struct mlx5e_priv *priv,
 		return false;
 	}
 
-	/* Might need to disable HW-GRO if it was kept on due to hds. */
-	if (tcp_data_split == ETHTOOL_TCP_DATA_SPLIT_DISABLED &&
-	    dev->cfg->hds_config == ETHTOOL_TCP_DATA_SPLIT_ENABLED)
-		netdev_update_features(priv->netdev);
+	if (tcp_data_split == ETHTOOL_TCP_DATA_SPLIT_DISABLED) {
+		NL_SET_ERR_MSG_MOD(extack,
+				   "TCP-data-split can not be disabled");
+		return false;
+	}
 
 	return true;
 }
@@ -468,13 +472,22 @@ static int mlx5e_set_ringparam(struct net_device *dev,
 			       struct netlink_ext_ack *extack)
 {
 	struct mlx5e_priv *priv = netdev_priv(dev);
+	int err;
 
 	if (!mlx5e_ethtool_set_tcp_data_split(priv,
 					      kernel_param->tcp_data_split,
 					      extack))
 		return -EINVAL;
 
-	return mlx5e_ethtool_set_ringparam(priv, param, extack);
+	err = mlx5e_ethtool_set_ringparam(priv, param, extack);
+	if (err)
+		return err;
+
+	/* Disable HW-GRO if it was only kept on for HDS. */
+	if (dev->cfg->hds_config != kernel_param->tcp_data_split)
+		netdev_update_features(priv->netdev);
+
+	return 0;
 }
 
 void mlx5e_ethtool_get_channels(struct mlx5e_priv *priv,
-- 
2.52.0