net: dsa: add support for DSA rx offloading via metadata dst

If a metadata dst is present with the type METADATA_HW_PORT_MUX on a dsa cpu
port netdev, assume that it carries the port number and that there is no DSA
tag present in the skb data.
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/core/flow_dissector.c

@@ -971,12 +971,14 @@ bool __skb_flow_dissect(const struct net *net,
 #if IS_ENABLED(CONFIG_NET_DSA)
 		if (unlikely(skb->dev && netdev_uses_dsa(skb->dev) &&
 			     proto == htons(ETH_P_XDSA))) {
+			struct metadata_dst *md_dst = skb_metadata_dst(skb);
 			const struct dsa_device_ops *ops;
 			int offset = 0;
 
 			ops = skb->dev->dsa_ptr->tag_ops;
 			/* Only DSA header taggers break flow dissection */
-			if (ops->needed_headroom) {
+			if (ops->needed_headroom &&
+			    (!md_dst || md_dst->type != METADATA_HW_PORT_MUX)) {
 				if (ops->flow_dissect)
 					ops->flow_dissect(skb, &proto, &offset);
 				else

net/dsa/dsa.c

@@ -11,6 +11,7 @@
 #include <linux/netdevice.h>
 #include <linux/sysfs.h>
 #include <linux/ptp_classify.h>
+#include <net/dst_metadata.h>
 
 #include "dsa_priv.h"
 
@@ -216,6 +217,7 @@ static bool dsa_skb_defer_rx_timestamp(struct dsa_slave_priv *p,
 static int dsa_switch_rcv(struct sk_buff *skb, struct net_device *dev,
 			  struct packet_type *pt, struct net_device *unused)
 {
+	struct metadata_dst *md_dst = skb_metadata_dst(skb);
 	struct dsa_port *cpu_dp = dev->dsa_ptr;
 	struct sk_buff *nskb = NULL;
 	struct dsa_slave_priv *p;
@@ -229,7 +231,22 @@ static int dsa_switch_rcv(struct sk_buff *skb, struct net_device *dev,
 	if (!skb)
 		return 0;
 
-	nskb = cpu_dp->rcv(skb, dev);
+	if (md_dst && md_dst->type == METADATA_HW_PORT_MUX) {
+		unsigned int port = md_dst->u.port_info.port_id;
+
+		skb_dst_drop(skb);
+		if (!skb_has_extensions(skb))
+			skb->slow_gro = 0;
+
+		skb->dev = dsa_master_find_slave(dev, 0, port);
+		if (likely(skb->dev)) {
+			dsa_default_offload_fwd_mark(skb);
+			nskb = skb;
+		}
+	} else {
+		nskb = cpu_dp->rcv(skb, dev);
+	}
+
 	if (!nskb) {
 		kfree_skb(skb);
 		return 0;