net: dsa: add NETC switch tag support

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>
Link: https://patch.msgid.link/20260518082506.1318236-10-wei.fang@nxp.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

1 files changed, 14 insertions, 0 deletions

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