Subject: [PATCH v7 net-next 09/15] net: dsa: add NETC switch tag support

From: Wei Fang <[email-masked]>
Date: Wed, 13 May 2026 11:04:48 +0800

The NXP NETC switch tag is a proprietary header added to frames after the
source MAC address. The switch tag has 3 types, and each type has 1 ~ 4
subtypes, the details are as follows.

Forward NXP switch tag (Type=0): Represents forwarded frames.
  - SubType = 0 - Normal frame processing.

To_Port NXP switch tag (Type=1): Represents frames that are to be sent
to a specific switch port.
  - SubType = 0. No request to perform timestamping.
  - SubType = 1. Request to perform one-step timestamping.
  - SubType = 2. Request to perform two-step timestamping.
  - SubType = 3. Request to perform both one-step timestamping and
    two-step timestamping.

To_Host NXP switch tag (Type=2): Represents frames redirected or copied
to the switch management port.
  - SubType = 0. Received frames redirected or copied to the switch
    management port.
  - SubType = 1. Received frames redirected or copied to the switch
    management port with captured timestamp at the switch port where
    the frame was received.
  - SubType = 2. Transmit timestamp response (two-step timestamping).

In addition, the length of different type switch tag is different, the
minimum length is 6 bytes, the maximum length is 14 bytes. Currently,
Forward tag, SubType 0 of To_Port tag and Subtype 0 of To_Host tag are
supported. More tags will be supported in the future.

Signed-off-by: Wei Fang <[email-masked]>
---
 include/linux/dsa/tag_netc.h  |  14 +++
 include/net/dsa.h             |   2 +
 include/uapi/linux/if_ether.h |   1 +
 net/dsa/Kconfig               |  10 ++
 net/dsa/Makefile              |   1 +
 net/dsa/tag_netc.c            | 214 ++++++++++++++++++++++++++++++++++
 6 files changed, 242 insertions(+)
 create mode 100644 include/linux/dsa/tag_netc.h
 create mode 100644 net/dsa/tag_netc.c

diff --git a/include/linux/dsa/tag_netc.h b/include/linux/dsa/tag_netc.h
new file mode 100644
index 000000000000..fe964722e5b0
--- /dev/null
+++ b/include/linux/dsa/tag_netc.h
@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0
+ *
+ * Copyright 2025-2026 NXP
+ */
+
+#ifndef __NET_DSA_TAG_NETC_H
+#define __NET_DSA_TAG_NETC_H
+
+#include <linux/skbuff.h>
+#include <net/dsa.h>
+
+#define NETC_TAG_MAX_LEN			14
+
+#endif
diff --git a/include/net/dsa.h b/include/net/dsa.h
index 4cc67469cf2e..8c16ef23cc10 100644
--- a/include/net/dsa.h
+++ b/include/net/dsa.h
@@ -58,6 +58,7 @@ struct tc_action;
 #define DSA_TAG_PROTO_YT921X_VALUE		30
 #define DSA_TAG_PROTO_MXL_GSW1XX_VALUE		31
 #define DSA_TAG_PROTO_MXL862_VALUE		32
+#define DSA_TAG_PROTO_NETC_VALUE		33
 
 enum dsa_tag_protocol {
 	DSA_TAG_PROTO_NONE		= DSA_TAG_PROTO_NONE_VALUE,
@@ -93,6 +94,7 @@ enum dsa_tag_protocol {
 	DSA_TAG_PROTO_YT921X		= DSA_TAG_PROTO_YT921X_VALUE,
 	DSA_TAG_PROTO_MXL_GSW1XX	= DSA_TAG_PROTO_MXL_GSW1XX_VALUE,
 	DSA_TAG_PROTO_MXL862		= DSA_TAG_PROTO_MXL862_VALUE,
+	DSA_TAG_PROTO_NETC		= DSA_TAG_PROTO_NETC_VALUE,
 };
 
 struct dsa_switch;
diff --git a/include/uapi/linux/if_ether.h b/include/uapi/linux/if_ether.h
index df9d44a11540..fb5efc8e06cc 100644
--- a/include/uapi/linux/if_ether.h
+++ b/include/uapi/linux/if_ether.h
@@ -123,6 +123,7 @@
 #define ETH_P_DSA_A5PSW	0xE001		/* A5PSW Tag Value [ NOT AN OFFICIALLY REGISTERED ID ] */
 #define ETH_P_IFE	0xED3E		/* ForCES inter-FE LFB type */
 #define ETH_P_AF_IUCV   0xFBFB		/* IBM af_iucv [ NOT AN OFFICIALLY REGISTERED ID ] */
+#define ETH_P_NXP_NETC  0xFD3A		/* NXP NETC DSA [ NOT AN OFFICIALLY REGISTERED ID ] */
 
 #define ETH_P_802_3_MIN	0x0600		/* If the value in the ethernet type is more than this value
 					 * then the frame is Ethernet II. Else it is 802.3 */
diff --git a/net/dsa/Kconfig b/net/dsa/Kconfig
index 5ed8c704636d..d5e725b90d78 100644
--- a/net/dsa/Kconfig
+++ b/net/dsa/Kconfig
@@ -125,6 +125,16 @@ config NET_DSA_TAG_KSZ
 	  Say Y if you want to enable support for tagging frames for the
 	  Microchip 8795/937x/9477/9893 families of switches.
 
+config NET_DSA_TAG_NETC
+	tristate "Tag driver for NXP NETC switches"
+	help
+	  Say Y or M if you want to enable support for the NXP Switch Tag (NST),
+	  as implemented by NXP NETC switches having version 4.3 or later. The
+	  switch tag is a proprietary header added to frames after the source
+	  MAC address, it has 3 types and each type has different subtypes, so
+	  its length depends on the type and subtype of the tag, the maximum
+	  length is 14 bytes.
+
 config NET_DSA_TAG_OCELOT
 	tristate "Tag driver for Ocelot family of switches, using NPI port"
 	select PACKING
diff --git a/net/dsa/Makefile b/net/dsa/Makefile
index bf7247759a64..b8c2667cd14a 100644
--- a/net/dsa/Makefile
+++ b/net/dsa/Makefile
@@ -30,6 +30,7 @@ obj-$(CONFIG_NET_DSA_TAG_LAN9303) += tag_lan9303.o
 obj-$(CONFIG_NET_DSA_TAG_MTK) += tag_mtk.o
 obj-$(CONFIG_NET_DSA_TAG_MXL_862XX) += tag_mxl862xx.o
 obj-$(CONFIG_NET_DSA_TAG_MXL_GSW1XX) += tag_mxl-gsw1xx.o
+obj-$(CONFIG_NET_DSA_TAG_NETC) += tag_netc.o
 obj-$(CONFIG_NET_DSA_TAG_NONE) += tag_none.o
 obj-$(CONFIG_NET_DSA_TAG_OCELOT) += tag_ocelot.o
 obj-$(CONFIG_NET_DSA_TAG_OCELOT_8021Q) += tag_ocelot_8021q.o
diff --git a/net/dsa/tag_netc.c b/net/dsa/tag_netc.c
new file mode 100644
index 000000000000..07684e0ff064
--- /dev/null
+++ b/net/dsa/tag_netc.c
@@ -0,0 +1,214 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright 2025-2026 NXP
+ */
+
+#include <linux/dsa/tag_netc.h>
+
+#include "tag.h"
+
+#define NETC_NAME			"nxp_netc"
+
+/* Forward NXP switch tag */
+#define NETC_TAG_FORWARD		0
+
+/* To_Port NXP switch tag */
+#define NETC_TAG_TO_PORT		1
+/* SubType0: No request to perform timestamping */
+#define NETC_TAG_TP_SUBTYPE0		0
+
+/* To_Host NXP switch tag */
+#define NETC_TAG_TO_HOST		2
+/* SubType0: frames redirected or copied to CPU port */
+#define NETC_TAG_TH_SUBTYPE0		0
+/* SubType1: frames redirected or copied to CPU port with timestamp */
+#define NETC_TAG_TH_SUBTYPE1		1
+/* SubType2: Transmit timestamp response (two-step timestamping) */
+#define NETC_TAG_TH_SUBTYPE2		2
+
+/* NETC switch tag lengths */
+#define NETC_TAG_FORWARD_LEN		6
+#define NETC_TAG_TP_SUBTYPE0_LEN	6
+#define NETC_TAG_TH_SUBTYPE0_LEN	6
+#define NETC_TAG_TH_SUBTYPE1_LEN	14
+#define NETC_TAG_TH_SUBTYPE2_LEN	14
+#define NETC_TAG_CMN_LEN		5
+
+#define NETC_TAG_SUBTYPE		GENMASK(3, 0)
+#define NETC_TAG_TYPE			GENMASK(7, 4)
+#define NETC_TAG_QV			BIT(0)
+#define NETC_TAG_IPV			GENMASK(4, 2)
+#define NETC_TAG_SWITCH			GENMASK(2, 0)
+#define NETC_TAG_PORT			GENMASK(7, 3)
+
+struct netc_tag_cmn {
+	__be16 tpid;
+	u8 type;
+	u8 qos;
+	u8 switch_port;
+} __packed;
+
+static void netc_fill_common_tag(struct netc_tag_cmn *tag, u8 type,
+				 u8 subtype, u8 sw_id, u8 port, u8 ipv)
+{
+	tag->tpid = htons(ETH_P_NXP_NETC);
+	tag->type = FIELD_PREP(NETC_TAG_TYPE, type) |
+		    FIELD_PREP(NETC_TAG_SUBTYPE, subtype);
+	tag->qos = NETC_TAG_QV | FIELD_PREP(NETC_TAG_IPV, ipv);
+	tag->switch_port = FIELD_PREP(NETC_TAG_SWITCH, sw_id) |
+			   FIELD_PREP(NETC_TAG_PORT, port);
+}
+
+static void *netc_fill_common_tp_tag(struct sk_buff *skb,
+				     struct net_device *ndev,
+				     u8 subtype, int tag_len)
+{
+	struct dsa_port *dp = dsa_user_to_port(ndev);
+	u16 queue = skb_get_queue_mapping(skb);
+	s8 ipv = netdev_txq_to_tc(ndev, queue);
+	void *tag;
+
+	if (unlikely(ipv < 0))
+		ipv = 0;
+
+	skb_push(skb, tag_len);
+	dsa_alloc_etype_header(skb, tag_len);
+
+	tag = dsa_etype_header_pos_tx(skb);
+	memset(tag + NETC_TAG_CMN_LEN, 0, tag_len - NETC_TAG_CMN_LEN);
+	/* As 'dsa,member' is a required property for NETC switch, the member
+	 * is used to specify the switch ID (thus the hardware switch ID and
+	 * the software switch ID are consistent), its range is 1 ~ 7. The
+	 * NETC switch driver will check this value, and if it is invalid,
+	 * the switch driver will fail the probe.
+	 * In addition, according to the nxp,netc-switch.yaml doc, the port
+	 * index will not be greater than 0xf.
+	 */
+	netc_fill_common_tag(tag, NETC_TAG_TO_PORT, subtype,
+			     dp->ds->index, dp->index, ipv);
+
+	return tag;
+}
+
+static void netc_fill_tp_tag_subtype0(struct sk_buff *skb,
+				      struct net_device *ndev)
+{
+	netc_fill_common_tp_tag(skb, ndev, NETC_TAG_TP_SUBTYPE0,
+				NETC_TAG_TP_SUBTYPE0_LEN);
+}
+
+/* Currently only support To_Port tag, subtype 0 */
+static struct sk_buff *netc_xmit(struct sk_buff *skb,
+				 struct net_device *ndev)
+{
+	netc_fill_tp_tag_subtype0(skb, ndev);
+
+	return skb;
+}
+
+static int netc_get_rx_tag_len(int type, int subtype)
+{
+	/* Only NETC_TAG_TO_HOST and NETC_TAG_FORWARD are expected in RX,
+	 * NETC_TAG_TO_PORT is a TX switch tag that does not exist in RX.
+	 */
+	if (type == NETC_TAG_TO_HOST) {
+		if (subtype == NETC_TAG_TH_SUBTYPE1)
+			return NETC_TAG_TH_SUBTYPE1_LEN;
+		else if (subtype == NETC_TAG_TH_SUBTYPE2)
+			return NETC_TAG_TH_SUBTYPE2_LEN;
+		else
+			return NETC_TAG_TH_SUBTYPE0_LEN;
+	}
+
+	return NETC_TAG_FORWARD_LEN;
+}
+
+static struct sk_buff *netc_rcv(struct sk_buff *skb,
+				struct net_device *ndev)
+{
+	struct netc_tag_cmn *tag_cmn;
+	int tag_len, sw_id, port;
+	int type, subtype;
+
+	if (unlikely(!pskb_may_pull(skb, NETC_TAG_MAX_LEN)))
+		return NULL;
+
+	tag_cmn = dsa_etype_header_pos_rx(skb);
+	if (ntohs(tag_cmn->tpid) != ETH_P_NXP_NETC) {
+		dev_warn_ratelimited(&ndev->dev, "Unknown TPID 0x%04x\n",
+				     ntohs(tag_cmn->tpid));
+
+		return NULL;
+	}
+
+	if (tag_cmn->qos & NETC_TAG_QV)
+		skb->priority = FIELD_GET(NETC_TAG_IPV, tag_cmn->qos);
+
+	sw_id = FIELD_GET(NETC_TAG_SWITCH, tag_cmn->switch_port);
+	/* ENETC VEPA switch ID (0) is not supported yet */
+	if (!sw_id) {
+		dev_warn_ratelimited(&ndev->dev,
+				     "VEPA switch ID is not supported yet\n");
+
+		return NULL;
+	}
+
+	port = FIELD_GET(NETC_TAG_PORT, tag_cmn->switch_port);
+	skb->dev = dsa_conduit_find_user(ndev, sw_id, port);
+	if (!skb->dev)
+		return NULL;
+
+	type = FIELD_GET(NETC_TAG_TYPE, tag_cmn->type);
+	subtype = FIELD_GET(NETC_TAG_SUBTYPE, tag_cmn->type);
+	if (type == NETC_TAG_FORWARD) {
+		dsa_default_offload_fwd_mark(skb);
+	} else if (type == NETC_TAG_TO_HOST) {
+		/* Currently only subtype0 supported */
+		if (subtype != NETC_TAG_TH_SUBTYPE0)
+			return NULL;
+	} else {
+		dev_warn_ratelimited(&ndev->dev,
+				     "Unknown tag type %d\n", type);
+		return NULL;
+	}
+
+	/* Remove Switch tag from the frame */
+	tag_len = netc_get_rx_tag_len(type, subtype);
+	skb_pull_rcsum(skb, tag_len);
+	dsa_strip_etype_header(skb, tag_len);
+
+	return skb;
+}
+
+static void netc_flow_dissect(const struct sk_buff *skb, __be16 *proto,
+			      int *offset)
+{
+	struct netc_tag_cmn *tag_cmn = (struct netc_tag_cmn *)(skb->data - 2);
+	int subtype = FIELD_GET(NETC_TAG_SUBTYPE, tag_cmn->type);
+	int type = FIELD_GET(NETC_TAG_TYPE, tag_cmn->type);
+	int tag_len = netc_get_rx_tag_len(type, subtype);
+
+	/* The RX minimum frame length of the NETC switch port is 64 bytes,
+	 * and the frame is received by the ENETC driver. From the hardware
+	 * perspective, the receive buffer of RX BD is at least 128 bytes,
+	 * so the switch tag header is guaranteed to be in the linear region
+	 * of the skb.
+	 */
+	*offset = tag_len;
+	*proto = ((__be16 *)skb->data)[(tag_len / 2) - 1];
+}
+
+static const struct dsa_device_ops netc_netdev_ops = {
+	.name			= NETC_NAME,
+	.proto			= DSA_TAG_PROTO_NETC,
+	.xmit			= netc_xmit,
+	.rcv			= netc_rcv,
+	.needed_headroom	= NETC_TAG_MAX_LEN,
+	.flow_dissect		= netc_flow_dissect,
+};
+
+MODULE_DESCRIPTION("DSA tag driver for NXP NETC switch family");
+MODULE_LICENSE("GPL");
+
+MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_NETC, NETC_NAME);
+module_dsa_tag_driver(netc_netdev_ops);
-- 
2.34.1