[PATCH net-next 09/14] net: dsa: add NETC switch tag support

Wei Fang
2026-03-16T09:41:31Z

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 <wei.fang@nxp.com>
---
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 | 180 ++++++++++++++++++++++++++++++++++
6 files changed, 208 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 6c17446f3dcc..6bed824d1f07 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..15b0dd5c5408
--- /dev/null
+++ b/net/dsa/tag_netc.c
@@ -0,0 +1,180 @@
+// 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);
+ u8 ipv = netdev_txq_to_tc(ndev, queue);
+ void *tag;
+
+ 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);
+ 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 rx_type)
+{
+ int type = FIELD_GET(NETC_TAG_TYPE, rx_type);
+
+ if (type == NETC_TAG_TO_HOST) {
+ u8 subtype = rx_type & NETC_TAG_SUBTYPE;
+
+ 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 = dsa_etype_header_pos_rx(skb);
+ int tag_len = netc_get_rx_tag_len(tag_cmn->type);
+ int sw_id, port;
+
+ 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 = 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;
+
+ if (tag_cmn->type == NETC_TAG_FORWARD)
+ dsa_default_offload_fwd_mark(skb);
+
+ /* Remove Switch tag from the frame */
+ 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 tag_len = netc_get_rx_tag_len(tag_cmn->type);
+
+ *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