[PATCH 3/4] net: dsa: Add support for SoC-e SDSA tags

[Vasilij Strassheim]

Add a DSA tagger for the SoC-e SDSA header format used between
the conduit and SoC-e switch ports.

The implementation adds TX tag insertion and RX tag parsing and
registers a new DSA tag protocol.

Signed-off-by: Vasilij Strassheim <v.strassheim@xxxxxxxxxxxxx>
---
 include/net/dsa.h  |   2 ++
 net/dsa/Kconfig    |   6 ++++
 net/dsa/Makefile   |   1 +
 net/dsa/tag_sdsa.c | 102 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 111 insertions(+)

diff --git a/include/net/dsa.h b/include/net/dsa.h
index 8c16ef23cc10..744bbb4d54ea 100644
--- a/include/net/dsa.h
+++ b/include/net/dsa.h
@@ -59,6 +59,7 @@ struct tc_action;
 #define DSA_TAG_PROTO_MXL_GSW1XX_VALUE		31
 #define DSA_TAG_PROTO_MXL862_VALUE		32
 #define DSA_TAG_PROTO_NETC_VALUE		33
+#define DSA_TAG_PROTO_SDSA_VALUE		34
 
 enum dsa_tag_protocol {
 	DSA_TAG_PROTO_NONE		= DSA_TAG_PROTO_NONE_VALUE,
@@ -95,6 +96,7 @@ enum dsa_tag_protocol {
 	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,
+	DSA_TAG_PROTO_SDSA		= DSA_TAG_PROTO_SDSA_VALUE,
 };
 
 struct dsa_switch;
diff --git a/net/dsa/Kconfig b/net/dsa/Kconfig
index d5e725b90d78..1e1b0f2fb726 100644
--- a/net/dsa/Kconfig
+++ b/net/dsa/Kconfig
@@ -98,6 +98,12 @@ config NET_DSA_TAG_EDSA
 	  Say Y or M if you want to enable support for tagging frames for the
 	  Marvell switches which use EtherType DSA headers.
 
+config NET_DSA_TAG_SDSA
+	tristate "Tag driver for SoC-e switches using EtherType SDSA headers"
+	help
+	  Say Y or M if you want to enable support for tagging frames for the
+	  SoC-e switches.
+
 config NET_DSA_TAG_MTK
 	tristate "Tag driver for Mediatek switches"
 	help
diff --git a/net/dsa/Makefile b/net/dsa/Makefile
index b8c2667cd14a..dc154f10e0a0 100644
--- a/net/dsa/Makefile
+++ b/net/dsa/Makefile
@@ -23,6 +23,7 @@ dsa_core-y += \
 obj-$(CONFIG_NET_DSA_TAG_AR9331) += tag_ar9331.o
 obj-$(CONFIG_NET_DSA_TAG_BRCM_COMMON) += tag_brcm.o
 obj-$(CONFIG_NET_DSA_TAG_DSA_COMMON) += tag_dsa.o
+obj-$(CONFIG_NET_DSA_TAG_SDSA) += tag_sdsa.o
 obj-$(CONFIG_NET_DSA_TAG_GSWIP) += tag_gswip.o
 obj-$(CONFIG_NET_DSA_TAG_HELLCREEK) += tag_hellcreek.o
 obj-$(CONFIG_NET_DSA_TAG_KSZ) += tag_ksz.o
diff --git a/net/dsa/tag_sdsa.c b/net/dsa/tag_sdsa.c
new file mode 100644
index 000000000000..b32dca1e367c
--- /dev/null
+++ b/net/dsa/tag_sdsa.c
@@ -0,0 +1,102 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 System on Chip engineering, S.L.
+ * Copyright (c) 2026 Linutronix GmbH
+ */
+
+#include <linux/bitops.h>
+#include <linux/etherdevice.h>
+
+#include "tag.h"
+
+#define SDSA_HLEN	8
+
+#define SDSA_NAME	"sdsa"
+#define ETH_P_SDSA	0xDCDC
+
+/* SDSA tag byte layout (after the 12-byte MAC header):
+ * Bytes 0-1: SDSA EtherType (0xDCDC)
+ * Bytes 2-3: Reserved
+ * Byte 4:    Frame type (bits 7-6), VLAN-info bit (bit 5), port[9:5] (bits 4-0)
+ * Byte 5:    Port[4:0] (bits 7-3)
+ * Bytes 6-7: PCP (bits 7-5) / CFI (bit 4) / VID (bits 3-0 + byte 7), only
+ *            meaningful when the VLAN-info bit is set.
+ */
+#define SDSA_TAG_FRAME_TYPE_MASK	GENMASK(7, 6)
+#define SDSA_TAG_VLAN_BIT		BIT(5)
+#define SDSA_TAG_PORT_HI_MASK		GENMASK(4, 0)
+#define SDSA_TAG_PORT_MASK		GENMASK(7, 3)
+
+static struct sk_buff *sdsa_xmit(struct sk_buff *skb, struct net_device *dev)
+{
+	struct dsa_port *dp = dsa_user_to_port(dev);
+	u8 *sdsa_header;
+
+	if (skb_cow_head(skb, SDSA_HLEN) < 0)
+		return NULL;
+
+	skb_push(skb, SDSA_HLEN);
+	dsa_alloc_etype_header(skb, SDSA_HLEN);
+
+	/* Construct the FROM_CPU DSA tag. */
+	sdsa_header = dsa_etype_header_pos_tx(skb);
+	sdsa_header[0] = (ETH_P_SDSA >> 8) & 0xff;
+	sdsa_header[1] = ETH_P_SDSA & 0xff;
+	sdsa_header[2] = 0x00; /* reserved */
+	sdsa_header[3] = 0x00; /* reserved */
+	sdsa_header[4] = FIELD_PREP(SDSA_TAG_FRAME_TYPE_MASK, 1) |
+			 FIELD_PREP(SDSA_TAG_PORT_HI_MASK, dp->index >> 5);
+	sdsa_header[5] = FIELD_PREP(SDSA_TAG_PORT_MASK, dp->index);
+	sdsa_header[6] = 0x00; /* VLAN not supported */
+	sdsa_header[7] = 0x00; /* VLAN not supported */
+
+	return skb;
+}
+
+static struct sk_buff *sdsa_rcv(struct sk_buff *skb, struct net_device *dev)
+{
+	u8 *sdsa_header;
+	int source_port;
+	u8 frame_type;
+
+	if (unlikely(!pskb_may_pull(skb, SDSA_HLEN)))
+		return NULL;
+
+	sdsa_header = dsa_etype_header_pos_rx(skb);
+
+	/* Check that the frame type is TO_CPU. */
+	frame_type = FIELD_GET(SDSA_TAG_FRAME_TYPE_MASK, sdsa_header[4]);
+	if (frame_type != 0)
+		return NULL;
+
+	/* VLAN-tagged traffic is intentionally unsupported yet. */
+	if (sdsa_header[4] & SDSA_TAG_VLAN_BIT)
+		return NULL;
+
+	/* Determine the source port from the two port fields. */
+	source_port = ((sdsa_header[4] & 0x1f) << 5) |
+		      ((sdsa_header[5] & 0xf8) >> 3);
+
+	skb->dev = dsa_conduit_find_user(dev, 0, source_port);
+	if (!skb->dev)
+		return NULL;
+
+	skb_pull_rcsum(skb, SDSA_HLEN);
+	dsa_strip_etype_header(skb, SDSA_HLEN);
+
+	dsa_default_offload_fwd_mark(skb);
+	return skb;
+}
+
+static const struct dsa_device_ops sdsa_netdev_ops = {
+	.name = SDSA_NAME,
+	.proto = DSA_TAG_PROTO_SDSA,
+	.xmit = sdsa_xmit,
+	.rcv = sdsa_rcv,
+	.needed_headroom = SDSA_HLEN,
+};
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("DSA tag driver for SoC-e SDSA protocol");
+MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_SDSA, SDSA_NAME);
+
+module_dsa_tag_driver(sdsa_netdev_ops);

-- 
2.39.5