net/mlx5e: CT: Add initial support for Hardware Steering

Connection tracking can offload tuple matches to the NIC either via
firmware commands (when the steering mode is dmfs or offload support is
disabled due to eswitch being set to legacy) or via software-managed
flow steering (smfs).

This commit adds stub operations for a third mode, hardware-managed flow
steering. This is enabled when both CONFIG_MLX5_TC_CT and
CONFIG_MLX5_HW_STEERING are enabled.

Signed-off-by: Cosmin Ratiu <cratiu@nvidia.com>
Reviewed-by: Jianbo Liu <jianbol@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/20250114130646.1937192-3-tariqt@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/mellanox/mlx5/core/Makefile

@@ -60,6 +60,7 @@ mlx5_core-$(CONFIG_MLX5_CLS_ACT)     += en/tc/act/act.o en/tc/act/drop.o en/tc/a
 ifneq ($(CONFIG_MLX5_TC_CT),)
 	mlx5_core-y			     += en/tc_ct.o en/tc/ct_fs_dmfs.o
 	mlx5_core-$(CONFIG_MLX5_SW_STEERING) += en/tc/ct_fs_smfs.o
+	mlx5_core-$(CONFIG_MLX5_HW_STEERING) += en/tc/ct_fs_hmfs.o
 endif
 
 mlx5_core-$(CONFIG_MLX5_TC_SAMPLE)   += en/tc/sample.o

drivers/net/ethernet/mellanox/mlx5/core/en/tc/ct_fs.h

@@ -48,4 +48,14 @@ mlx5_ct_fs_smfs_ops_get(void)
 }
 #endif /* IS_ENABLED(CONFIG_MLX5_SW_STEERING) */
 
+#if IS_ENABLED(CONFIG_MLX5_HW_STEERING)
+struct mlx5_ct_fs_ops *mlx5_ct_fs_hmfs_ops_get(void);
+#else
+static inline struct mlx5_ct_fs_ops *
+mlx5_ct_fs_hmfs_ops_get(void)
+{
+	return NULL;
+}
+#endif /* IS_ENABLED(CONFIG_MLX5_SW_STEERING) */
+
 #endif /* __MLX5_EN_TC_CT_FS_H__ */

drivers/net/ethernet/mellanox/mlx5/core/en/tc/ct_fs_hmfs.c

@@ -0,0 +1,47 @@
+// SPDX-License-Identifier: GPL-2.0 OR Linux-OpenIB
+/* Copyright (c) 2025, NVIDIA CORPORATION & AFFILIATES. */
+
+#include "en_tc.h"
+#include "en/tc_ct.h"
+#include "en/tc/ct_fs.h"
+
+static int mlx5_ct_fs_hmfs_init(struct mlx5_ct_fs *fs, struct mlx5_flow_table *ct,
+				struct mlx5_flow_table *ct_nat, struct mlx5_flow_table *post_ct)
+{
+	return 0;
+}
+
+static void mlx5_ct_fs_hmfs_destroy(struct mlx5_ct_fs *fs)
+{
+}
+
+static struct mlx5_ct_fs_rule *
+mlx5_ct_fs_hmfs_ct_rule_add(struct mlx5_ct_fs *fs, struct mlx5_flow_spec *spec,
+			    struct mlx5_flow_attr *attr, struct flow_rule *flow_rule)
+{
+	return ERR_PTR(-EOPNOTSUPP);
+}
+
+static void mlx5_ct_fs_hmfs_ct_rule_del(struct mlx5_ct_fs *fs, struct mlx5_ct_fs_rule *fs_rule)
+{
+}
+
+static int mlx5_ct_fs_hmfs_ct_rule_update(struct mlx5_ct_fs *fs, struct mlx5_ct_fs_rule *fs_rule,
+					  struct mlx5_flow_spec *spec, struct mlx5_flow_attr *attr)
+{
+	return -EOPNOTSUPP;
+}
+
+static struct mlx5_ct_fs_ops hmfs_ops = {
+	.ct_rule_add = mlx5_ct_fs_hmfs_ct_rule_add,
+	.ct_rule_del = mlx5_ct_fs_hmfs_ct_rule_del,
+	.ct_rule_update = mlx5_ct_fs_hmfs_ct_rule_update,
+
+	.init = mlx5_ct_fs_hmfs_init,
+	.destroy = mlx5_ct_fs_hmfs_destroy,
+};
+
+struct mlx5_ct_fs_ops *mlx5_ct_fs_hmfs_ops_get(void)
+{
+	return &hmfs_ops;
+}

drivers/net/ethernet/mellanox/mlx5/core/en/tc_ct.c

@@ -2065,10 +2065,19 @@ mlx5_tc_ct_fs_init(struct mlx5_tc_ct_priv *ct_priv)
 	struct mlx5_ct_fs_ops *fs_ops = mlx5_ct_fs_dmfs_ops_get();
 	int err;
 
-	if (ct_priv->ns_type == MLX5_FLOW_NAMESPACE_FDB &&
-	    ct_priv->dev->priv.steering->mode == MLX5_FLOW_STEERING_MODE_SMFS) {
-		ct_dbg("Using SMFS ct flow steering provider");
-		fs_ops = mlx5_ct_fs_smfs_ops_get();
+	if (ct_priv->ns_type == MLX5_FLOW_NAMESPACE_FDB) {
+		if (ct_priv->dev->priv.steering->mode == MLX5_FLOW_STEERING_MODE_HMFS) {
+			ct_dbg("Using HMFS ct flow steering provider");
+			fs_ops = mlx5_ct_fs_hmfs_ops_get();
+		} else if (ct_priv->dev->priv.steering->mode == MLX5_FLOW_STEERING_MODE_SMFS) {
+			ct_dbg("Using SMFS ct flow steering provider");
+			fs_ops = mlx5_ct_fs_smfs_ops_get();
+		}
+
+		if (!fs_ops) {
+			ct_dbg("Requested flow steering mode is not enabled.");
+			return -EOPNOTSUPP;
+		}
 	}
 
 	ct_priv->fs = kzalloc(sizeof(*ct_priv->fs) + fs_ops->priv_size, GFP_KERNEL);