net: ethernet: mtk_eth_soc: fix L2 offloading with DSA untag offload

Check for skb metadata in order to detect the case where the DSA header
is not present.

Fixes: 2d7605a7 ("net: ethernet: mtk_eth_soc: enable hardware DSA untagging")
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Link: https://lore.kernel.org/r/20230330120840.52079-2-nbd@nbd.nameSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/mediatek/mtk_eth_soc.c

@@ -2057,9 +2057,6 @@ static int mtk_poll_rx(struct napi_struct *napi, int budget,
 			skb_checksum_none_assert(skb);
 		skb->protocol = eth_type_trans(skb, netdev);
 
-		if (reason == MTK_PPE_CPU_REASON_HIT_UNBIND_RATE_REACHED)
-			mtk_ppe_check_skb(eth->ppe[0], skb, hash);
-
 		if (netdev->features & NETIF_F_HW_VLAN_CTAG_RX) {
 			if (MTK_HAS_CAPS(eth->soc->caps, MTK_NETSYS_V2)) {
 				if (trxd.rxd3 & RX_DMA_VTAG_V2) {
@@ -2087,6 +2084,9 @@ static int mtk_poll_rx(struct napi_struct *napi, int budget,
 			__vlan_hwaccel_put_tag(skb, htons(vlan_proto), vlan_tci);
 		}
 
+		if (reason == MTK_PPE_CPU_REASON_HIT_UNBIND_RATE_REACHED)
+			mtk_ppe_check_skb(eth->ppe[0], skb, hash);
+
 		skb_record_rx_queue(skb, 0);
 		napi_gro_receive(napi, skb);
 

drivers/net/ethernet/mediatek/mtk_ppe.c

@@ -8,6 +8,7 @@
 #include <linux/platform_device.h>
 #include <linux/if_ether.h>
 #include <linux/if_vlan.h>
+#include <net/dst_metadata.h>
 #include <net/dsa.h>
 #include "mtk_eth_soc.h"
 #include "mtk_ppe.h"
@@ -699,7 +700,9 @@ void __mtk_ppe_check_skb(struct mtk_ppe *ppe, struct sk_buff *skb, u16 hash)
 		    skb->dev->dsa_ptr->tag_ops->proto != DSA_TAG_PROTO_MTK)
 			goto out;
 
+		if (!skb_metadata_dst(skb))
 			tag += 4;
+
 		if (get_unaligned_be16(tag) != ETH_P_8021Q)
 			break;