[PATCH 5.4 09/45] net: ethernet: mtk_eth_soc: fix tx vlan tag for llc packets

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

5.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Felix Fietkau <nbd@nbd.name>

[ Upstream commit d4736737110ffa83d29f1c5d17b26113864205f6 ]

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>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250831182007.51619-1-nbd@nbd.name
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/net/ethernet/mediatek/mtk_eth_soc.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
index 7b9f5eba78dcc..6ab4c84bc22ef 100644
--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
@@ -1173,6 +1173,13 @@ static int mtk_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	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
@@ -1218,8 +1225,9 @@ static int mtk_start_xmit(struct sk_buff *skb, struct net_device *dev)
 
 drop:
 	spin_unlock(&eth->page_lock);
-	stats->tx_dropped++;
 	dev_kfree_skb_any(skb);
+dropped:
+	stats->tx_dropped++;
 	return NETDEV_TX_OK;
 }
 
-- 
2.50.1