net/mlx5e: Support XDP target xmit with dummy program

Save per-channel resources in default, in device and host memory.

As no better API exist, make the XDP-redirect-target SQ available by
loading a dummy XDP program.

This improves the latency of interface up/down operations when feature
is disabled.

Perf numbers:
NIC: Connect-X7.
Setup: 248 channels, default mtu and rx/tx ring sizes.

Interface up + down:
Before: 2.246 secs
After:  1.798 secs (-0.448 sec)

Saves ~1.8 msec per channel.

Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Dragos Tatulea <dtatulea@nvidia.com>
Reviewed-by: William Tu <witu@nvidia.com>
Link: https://patch.msgid.link/1764497617-1326331-3-git-send-email-tariqt@nvidia.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Author: Tariq Toukan

drivers/net/ethernet/mellanox/mlx5/core/en_main.c

@@ -2612,7 +2612,7 @@ static int mlx5e_open_queues(struct mlx5e_channel *c,
 	if (err)
 		goto err_close_icosq_cq;
 
-	if (netdev_ops->ndo_xdp_xmit) {
+	if (netdev_ops->ndo_xdp_xmit && c->xdp) {
 		c->xdpsq = mlx5e_open_xdpredirect_sq(c, params, cparam, &ccp);
 		if (IS_ERR(c->xdpsq)) {
 			err = PTR_ERR(c->xdpsq);
@@ -4415,19 +4415,18 @@ void mlx5e_set_xdp_feature(struct mlx5e_priv *priv)
 {
 	struct mlx5e_params *params = &priv->channels.params;
 	struct net_device *netdev = priv->netdev;
-	xdp_features_t val;
+	xdp_features_t val = 0;
 
-	if (!netdev->netdev_ops->ndo_bpf ||
-	    params->packet_merge.type != MLX5E_PACKET_MERGE_NONE) {
-		xdp_set_features_flag_locked(netdev, 0);
-		return;
-	}
+	if (netdev->netdev_ops->ndo_bpf &&
+	    params->packet_merge.type == MLX5E_PACKET_MERGE_NONE)
+		val = NETDEV_XDP_ACT_BASIC | NETDEV_XDP_ACT_REDIRECT |
+		      NETDEV_XDP_ACT_XSK_ZEROCOPY |
+		      NETDEV_XDP_ACT_RX_SG;
+
+	if (netdev->netdev_ops->ndo_xdp_xmit && params->xdp_prog)
+		val |= NETDEV_XDP_ACT_NDO_XMIT |
+			NETDEV_XDP_ACT_NDO_XMIT_SG;
 
-	val = NETDEV_XDP_ACT_BASIC | NETDEV_XDP_ACT_REDIRECT |
-	      NETDEV_XDP_ACT_XSK_ZEROCOPY |
-	      NETDEV_XDP_ACT_RX_SG |
-	      NETDEV_XDP_ACT_NDO_XMIT |
-	      NETDEV_XDP_ACT_NDO_XMIT_SG;
 	xdp_set_features_flag_locked(netdev, val);
 }