[PATCH v3 net-next 1/2] net: dsa: tag_yt922x: add support for Motorcomm YT922x tags

[Kyle Switch]

For the Motorcomm YT922x series, tag are supported, and with a
default TPID(Tag Protocol Identifier) 0x9988, and the tag occupies
8 bytes.

Signed-off-by: Kyle Switch <kyle.switch@xxxxxxxxxxxxxx>
---
 include/net/dsa.h    |   2 +
 net/dsa/Kconfig      |   6 +++
 net/dsa/Makefile     |   1 +
 net/dsa/tag_yt922x.c | 111 +++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 120 insertions(+)
 create mode 100644 net/dsa/tag_yt922x.c

diff --git a/include/net/dsa.h b/include/net/dsa.h
index 7507d632e7c6..d1c4f2abc8e1 100644
--- a/include/net/dsa.h
+++ b/include/net/dsa.h
@@ -61,6 +61,7 @@ struct tc_action;
 #define DSA_TAG_PROTO_NETC_VALUE		33
 #define DSA_TAG_PROTO_KSZ8463_VALUE		34
 #define DSA_TAG_PROTO_MT7628_VALUE		35
+#define DSA_TAG_PROTO_YT922X_VALUE              36
 
 enum dsa_tag_protocol {
 	DSA_TAG_PROTO_NONE		= DSA_TAG_PROTO_NONE_VALUE,
@@ -99,6 +100,7 @@ enum dsa_tag_protocol {
 	DSA_TAG_PROTO_NETC		= DSA_TAG_PROTO_NETC_VALUE,
 	DSA_TAG_PROTO_KSZ8463		= DSA_TAG_PROTO_KSZ8463_VALUE,
 	DSA_TAG_PROTO_MT7628		= DSA_TAG_PROTO_MT7628_VALUE,
+	DSA_TAG_PROTO_YT922X		= DSA_TAG_PROTO_YT922X_VALUE,
 };
 
 struct dsa_switch;
diff --git a/net/dsa/Kconfig b/net/dsa/Kconfig
index 23b4b74004ed..0b9f8a632cf2 100644
--- a/net/dsa/Kconfig
+++ b/net/dsa/Kconfig
@@ -227,4 +227,10 @@ 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_YT922X
+	tristate "Tag driver for Motorcomm YT922x switches"
+	help
+	  Say Y or M if you want to enable support for tagging frames for
+	  Motorcomm YT922x switches.
+
 endif
diff --git a/net/dsa/Makefile b/net/dsa/Makefile
index d15bcf5c68f0..0c53f4184bdb 100644
--- a/net/dsa/Makefile
+++ b/net/dsa/Makefile
@@ -44,6 +44,7 @@ obj-$(CONFIG_NET_DSA_TAG_TRAILER) += tag_trailer.o
 obj-$(CONFIG_NET_DSA_TAG_VSC73XX_8021Q) += tag_vsc73xx_8021q.o
 obj-$(CONFIG_NET_DSA_TAG_XRS700X) += tag_xrs700x.o
 obj-$(CONFIG_NET_DSA_TAG_YT921X) += tag_yt921x.o
+obj-$(CONFIG_NET_DSA_TAG_YT922X) += tag_yt922x.o
 
 # for tracing framework to find trace.h
 CFLAGS_trace.o := -I$(src)
diff --git a/net/dsa/tag_yt922x.c b/net/dsa/tag_yt922x.c
new file mode 100644
index 000000000000..d973c1e02cc1
--- /dev/null
+++ b/net/dsa/tag_yt922x.c
@@ -0,0 +1,111 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Motorcomm YT922x Switch Extended CPU Port Tagging
+ *
+ * Copyright (c) 2026 Kyle switch <kyle.switch@xxxxxxxxxxxxxx>
+ *
+ */
+
+#include <linux/etherdevice.h>
+
+#include "tag.h"
+
+#define YT922X_TAG_LEN	8
+
+/*
+ * To define the from cpu tag format 8 bytes:
+ */
+#define YT922X_TAG_NAME			"yt922x"
+#define YT922X_TAG_PORTMASK_0		BIT(15)
+#define YT922X_TAG_PORTMASK_M		GENMASK(8, 0)
+#define  YT922X_TAG_PORTS(x)			FIELD_PREP(YT922X_TAG_PORTMASK_M, ((x) >> 0x1))
+#define YT922X_TAG_FORCE_DST		BIT(9)
+#define YT922X_TAG_PRIO_M		GENMASK(12, 10)
+#define YT922X_TAG_PRIO_EN		BIT(13)
+#define  YT922X_TAG_PRIO(x)			(FIELD_PREP(YT922X_TAG_PRIO_M, (x)) | YT922X_TAG_PRIO_EN)
+#define YT922X_TAG_RX_PORT_M		GENMASK(5, 2)
+#define YT922X_TAG_RX_PRIO_M		GENMASK(15, 13)
+
+static struct sk_buff *
+yt922x_tag_xmit(struct sk_buff *skb, struct net_device *netdev)
+{
+	struct dsa_port *dp = dsa_user_to_port(netdev);
+	__be16 *tag;
+	u16 ctrl;
+
+	skb_push(skb, YT922X_TAG_LEN);
+	dsa_alloc_etype_header(skb, YT922X_TAG_LEN);
+	tag = dsa_etype_header_pos_tx(skb);
+
+	tag[0] = htons(ETH_P_YT921X);
+	if (dp->index != 0) {
+		/* Port index is not equal 0 in tag[1] */
+		ctrl = YT922X_TAG_PRIO(skb->priority) | YT922X_TAG_FORCE_DST |
+			YT922X_TAG_PORTS(dsa_xmit_port_mask(skb, netdev));
+		tag[1] = htons(ctrl);
+		tag[2] = 0;
+	} else {
+		/* Port 0 in bit15 in tag[2] */
+		ctrl = YT922X_TAG_PRIO(skb->priority) | YT922X_TAG_FORCE_DST;
+		tag[1] = htons(ctrl);
+		ctrl = YT922X_TAG_PORTMASK_0;
+		tag[2] = htons(ctrl);
+	}
+	tag[3] = 0;
+
+	return skb;
+}
+
+static struct sk_buff *
+yt922x_tag_rcv(struct sk_buff *skb, struct net_device *netdev)
+{
+	unsigned int port;
+	__be16 *tag;
+	u16 rx;
+
+	if (unlikely(!pskb_may_pull(skb, YT922X_TAG_LEN))) {
+		kfree_skb(skb);
+		return NULL;
+	}
+
+	tag = dsa_etype_header_pos_rx(skb);
+
+	if (unlikely(tag[0] != htons(ETH_P_YT921X))) {
+		dev_warn_ratelimited(&netdev->dev,
+				     "Unexpected EtherType 0x%04x\n",
+				     ntohs(tag[0]));
+		kfree_skb(skb);
+		return NULL;
+	}
+
+	/* Locate which port this is coming from */
+	rx = ntohs(tag[2]);
+	port = FIELD_GET(YT922X_TAG_RX_PORT_M, rx);
+	skb->dev = dsa_conduit_find_user(netdev, 0, port);
+	if (unlikely(!skb->dev)) {
+		dev_warn_ratelimited(&netdev->dev,
+				     "Couldn't decode source port %u\n", port);
+		kfree_skb(skb);
+		return NULL;
+	}
+
+	/* Remove tag and update checksum */
+	skb_pull_rcsum(skb, YT922X_TAG_LEN);
+	dsa_strip_etype_header(skb, YT922X_TAG_LEN);
+
+	return skb;
+}
+
+static const struct dsa_device_ops yt922x_netdev_ops = {
+	.name   = YT922X_TAG_NAME,
+	.proto  = DSA_TAG_PROTO_YT922X,
+	.xmit   = yt922x_tag_xmit,
+	.rcv    = yt922x_tag_rcv,
+	.needed_headroom = YT922X_TAG_LEN,
+};
+
+MODULE_DESCRIPTION("DSA tag driver for Motorcomm YT922x switches");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_YT922X, YT922X_TAG_NAME);
+
+module_dsa_tag_driver(yt922x_netdev_ops);
-- 
2.25.1