From: Felix Fietkau <nbd@nbd.name>
Date: Sun, 31 Aug 2025 20:05:13 +0200
Subject: [PATCH] net: ethernet: mtk_eth_soc: fix tx vlan tag for llc packets

When sending llc packets with vlan tx offload, the hardware fails to
actually add the tag. Deal with this by fixing it up in software.

Fixes: 656e705243fd ("net-next: mediatek: add support for MT7623 ethernet")
Reported-by: Thibaut VARENE <hacks@slashdirt.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>
---

--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
@@ -1763,6 +1763,13 @@ static netdev_tx_t mtk_start_xmit(struct
 	bool gso = false;
 	int tx_num;
 
+	if (skb_vlan_tag_present(skb) &&
+	    !eth_proto_is_802_3(eth_hdr(skb)->h_proto)) {
+		skb = __vlan_hwaccel_push_inside(skb);
+		if (!skb)
+			goto dropped;
+	}
+
 	/* normally we can rely on the stack not calling this more than once,
 	 * however we have 2 queues running on the same ring so we need to lock
 	 * the ring access
@@ -1826,8 +1833,9 @@ static netdev_tx_t mtk_start_xmit(struct
 
 drop:
 	spin_unlock(&eth->page_lock);
-	stats->tx_dropped++;
 	dev_kfree_skb_any(skb);
+dropped:
+	stats->tx_dropped++;
 	return NETDEV_TX_OK;
 }
 
