netdev - [PATCH net] net: ethernet: mtk_eth_soc: fix tx vlan tag for llc packets

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Message-ID: <20250831182007.51619-1-nbd@nbd.name>
Date: Sun, 31 Aug 2025 20:20:07 +0200
From: Felix Fietkau <nbd@....name>
To: netdev@...r.kernel.org,
	hacks@...shdirt.org,
	Sean Wang <sean.wang@...iatek.com>,
	Lorenzo Bianconi <lorenzo@...nel.org>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	Michael Lee <igvtee@...il.com>,
	John Crispin <john@...ozen.org>
Subject: [PATCH net] 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@...shdirt.org>
Signed-off-by: Felix Fietkau <nbd@....name>
---
 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 5a5fcde76dc0..e68997a29191 100644
--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
@@ -1761,6 +1761,13 @@ static netdev_tx_t 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
@@ -1806,8 +1813,9 @@ static netdev_tx_t 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;
 }
 
-- 
2.51.0