FAILED: patch "[PATCH] net: dsa: tag_mtk: fix 802.1ad VLAN egress" failed to apply to 5.10-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 5.10-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 9200f515c41f4cbaeffd8fdd1d8b6373a18b1b67 Mon Sep 17 00:00:00 2001
From: DENG Qingfang <dqfext@gmail.com>
Date: Tue, 2 Mar 2021 00:01:59 +0800
Subject: [PATCH] net: dsa: tag_mtk: fix 802.1ad VLAN egress

A different TPID bit is used for 802.1ad VLAN frames.

Reported-by: Ilario Gelmetti <iochesonome@gmail.com>
Fixes: f0af34317f4b ("net: dsa: mediatek: combine MediaTek tag with VLAN tag")
Signed-off-by: DENG Qingfang <dqfext@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/dsa/tag_mtk.c b/net/dsa/tag_mtk.c
index 38dcdded74c0..59748487664f 100644
--- a/net/dsa/tag_mtk.c
+++ b/net/dsa/tag_mtk.c
@@ -13,6 +13,7 @@
 #define MTK_HDR_LEN		4
 #define MTK_HDR_XMIT_UNTAGGED		0
 #define MTK_HDR_XMIT_TAGGED_TPID_8100	1
+#define MTK_HDR_XMIT_TAGGED_TPID_88A8	2
 #define MTK_HDR_RECV_SOURCE_PORT_MASK	GENMASK(2, 0)
 #define MTK_HDR_XMIT_DP_BIT_MASK	GENMASK(5, 0)
 #define MTK_HDR_XMIT_SA_DIS		BIT(6)
@@ -21,8 +22,8 @@ static struct sk_buff *mtk_tag_xmit(struct sk_buff *skb,
 				    struct net_device *dev)
 {
 	struct dsa_port *dp = dsa_slave_to_port(dev);
+	u8 xmit_tpid;
 	u8 *mtk_tag;
-	bool is_vlan_skb = true;
 	unsigned char *dest = eth_hdr(skb)->h_dest;
 	bool is_multicast_skb = is_multicast_ether_addr(dest) &&
 				!is_broadcast_ether_addr(dest);
@@ -33,10 +34,17 @@ static struct sk_buff *mtk_tag_xmit(struct sk_buff *skb,
 	 * the both special and VLAN tag at the same time and then look up VLAN
 	 * table with VID.
 	 */
-	if (!skb_vlan_tagged(skb)) {
+	switch (skb->protocol) {
+	case htons(ETH_P_8021Q):
+		xmit_tpid = MTK_HDR_XMIT_TAGGED_TPID_8100;
+		break;
+	case htons(ETH_P_8021AD):
+		xmit_tpid = MTK_HDR_XMIT_TAGGED_TPID_88A8;
+		break;
+	default:
+		xmit_tpid = MTK_HDR_XMIT_UNTAGGED;
 		skb_push(skb, MTK_HDR_LEN);
 		memmove(skb->data, skb->data + MTK_HDR_LEN, 2 * ETH_ALEN);
-		is_vlan_skb = false;
 	}
 
 	mtk_tag = skb->data + 2 * ETH_ALEN;
@@ -44,8 +52,7 @@ static struct sk_buff *mtk_tag_xmit(struct sk_buff *skb,
 	/* Mark tag attribute on special tag insertion to notify hardware
 	 * whether that's a combined special tag with 802.1Q header.
 	 */
-	mtk_tag[0] = is_vlan_skb ? MTK_HDR_XMIT_TAGGED_TPID_8100 :
-		     MTK_HDR_XMIT_UNTAGGED;
+	mtk_tag[0] = xmit_tpid;
 	mtk_tag[1] = (1 << dp->index) & MTK_HDR_XMIT_DP_BIT_MASK;
 
 	/* Disable SA learning for multicast frames */
@@ -53,7 +60,7 @@ static struct sk_buff *mtk_tag_xmit(struct sk_buff *skb,
 		mtk_tag[1] |= MTK_HDR_XMIT_SA_DIS;
 
 	/* Tag control information is kept for 802.1Q */
-	if (!is_vlan_skb) {
+	if (xmit_tpid == MTK_HDR_XMIT_UNTAGGED) {
 		mtk_tag[2] = 0;
 		mtk_tag[3] = 0;
 	}