[PATCH 09/20] net: dsa: tag_xlnx_tsn: add skeleton tag protocol

The AMD/Xilinx TSN Endpoint Ethernet MAC IP does not insert an
in-band CPU tag on the wire. The EP MAC driver attaches a per-port
metadata_dst (METADATA_HW_PORT_MUX) on RX to carry the port
classification out of band. The tag protocol therefore has no tag
bytes to add or strip.

Add DSA_TAG_PROTO_XLNX_TSN and register NET_DSA_TAG_XLNX_TSN as a
no-op tag driver. A later patch adds the PTP TX intercept to reroute
PTP frames through the per-MAC PTP TX path.

Signed-off-by: Nagadheeraj Rottela <[email protected]>
---
 MAINTAINERS            |  1 +
 include/net/dsa.h      |  2 ++
 net/dsa/Kconfig        |  9 +++++++++
 net/dsa/Makefile       |  1 +
 net/dsa/tag_xlnx_tsn.c | 33 +++++++++++++++++++++++++++++++++
 5 files changed, 46 insertions(+)
 create mode 100644 net/dsa/tag_xlnx_tsn.c

diff --git a/MAINTAINERS b/MAINTAINERS
index e5b95b3bfa21..6fbe83fb3953 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -29614,6 +29614,7 @@ L:	[email protected]
 S:	Maintained
 F:	Documentation/devicetree/bindings/net/xlnx,tsn-endpoint-ethernet-mac.yaml
 F:	drivers/net/ethernet/xilinx/tsn/
+F:	net/dsa/tag_xlnx_tsn.c
 
 XILINX UARTLITE SERIAL DRIVER
 M:	Peter Korsgaard <[email protected]>
diff --git a/include/net/dsa.h b/include/net/dsa.h
index 6f7f5c17b532..f0cc5b49407a 100644
--- a/include/net/dsa.h
+++ b/include/net/dsa.h
@@ -60,6 +60,7 @@ struct tc_action;
 #define DSA_TAG_PROTO_MXL862_VALUE		32
 #define DSA_TAG_PROTO_NETC_VALUE		33
 #define DSA_TAG_PROTO_KSZ8463_VALUE		34
+#define DSA_TAG_PROTO_XLNX_TSN_VALUE		35
 
 enum dsa_tag_protocol {
 	DSA_TAG_PROTO_NONE		= DSA_TAG_PROTO_NONE_VALUE,
@@ -97,6 +98,7 @@ enum dsa_tag_protocol {
 	DSA_TAG_PROTO_MXL862		= DSA_TAG_PROTO_MXL862_VALUE,
 	DSA_TAG_PROTO_NETC		= DSA_TAG_PROTO_NETC_VALUE,
 	DSA_TAG_PROTO_KSZ8463		= DSA_TAG_PROTO_KSZ8463_VALUE,
+	DSA_TAG_PROTO_XLNX_TSN		= DSA_TAG_PROTO_XLNX_TSN_VALUE,
 };
 
 struct dsa_switch;
diff --git a/net/dsa/Kconfig b/net/dsa/Kconfig
index d5e725b90d78..8ca48ce46ec1 100644
--- a/net/dsa/Kconfig
+++ b/net/dsa/Kconfig
@@ -221,4 +221,13 @@ config NET_DSA_TAG_YT921X
 	  Say Y or M if you want to enable support for tagging frames for
 	  Motorcomm YT921x switches.
 
+config NET_DSA_TAG_XLNX_TSN
+	tristate "Tag driver for AMD/Xilinx TSN Endpoint Ethernet MAC"
+	help
+	  Say Y or M if you want to enable support for the AMD/Xilinx TSN
+	  Endpoint Ethernet MAC IP. The IP does not insert an in-band CPU
+	  tag; port classification is conveyed via metadata_dst attached on
+	  RX by the EP MAC driver, and PTP TX frames are intercepted in the
+	  xmit hook to be steered into the per-MAC PTP TX register window.
+
 endif
diff --git a/net/dsa/Makefile b/net/dsa/Makefile
index b8c2667cd14a..6ba6c3a95976 100644
--- a/net/dsa/Makefile
+++ b/net/dsa/Makefile
@@ -41,6 +41,7 @@ obj-$(CONFIG_NET_DSA_TAG_RZN1_A5PSW) += tag_rzn1_a5psw.o
 obj-$(CONFIG_NET_DSA_TAG_SJA1105) += tag_sja1105.o
 obj-$(CONFIG_NET_DSA_TAG_TRAILER) += tag_trailer.o
 obj-$(CONFIG_NET_DSA_TAG_VSC73XX_8021Q) += tag_vsc73xx_8021q.o
+obj-$(CONFIG_NET_DSA_TAG_XLNX_TSN) += tag_xlnx_tsn.o
 obj-$(CONFIG_NET_DSA_TAG_XRS700X) += tag_xrs700x.o
 obj-$(CONFIG_NET_DSA_TAG_YT921X) += tag_yt921x.o
 
diff --git a/net/dsa/tag_xlnx_tsn.c b/net/dsa/tag_xlnx_tsn.c
new file mode 100644
index 000000000000..de352aa3d9a8
--- /dev/null
+++ b/net/dsa/tag_xlnx_tsn.c
@@ -0,0 +1,33 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * AMD/Xilinx TSN Endpoint Ethernet MAC tag protocol.
+ */
+
+#include "tag.h"
+
+#define XLNX_TSN_NAME	"xlnx_tsn"
+
+static struct sk_buff *xlnx_tsn_xmit(struct sk_buff *skb,
+				     struct net_device *dev)
+{
+	return skb;
+}
+
+static struct sk_buff *xlnx_tsn_rcv(struct sk_buff *skb,
+				    struct net_device *dev)
+{
+	kfree_skb(skb);
+	return NULL;
+}
+
+static const struct dsa_device_ops xlnx_tsn_netdev_ops = {
+	.name	= XLNX_TSN_NAME,
+	.proto	= DSA_TAG_PROTO_XLNX_TSN,
+	.xmit	= xlnx_tsn_xmit,
+	.rcv	= xlnx_tsn_rcv,
+};
+
+module_dsa_tag_driver(xlnx_tsn_netdev_ops);
+MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_XLNX_TSN, XLNX_TSN_NAME);
+MODULE_DESCRIPTION("DSA tag driver for AMD/Xilinx TSN Endpoint Ethernet MAC");
+MODULE_LICENSE("GPL");
-- 
2.34.1