From ef07df397a621707903ef0d294a7df11f80cf206 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=81lvaro=20Fern=C3=A1ndez=20Rojas?= <noltari@gmail.com>
Date: Sat, 14 Jun 2025 09:59:48 +0200
Subject: [PATCH] net: dsa: tag_brcm: add support for legacy FCS tags
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Add support for legacy Broadcom FCS tags, which are similar to
DSA_TAG_PROTO_BRCM_LEGACY.
BCM5325 and BCM5365 switches require including the original FCS value and
length, as opposed to BCM63xx switches.
Adding the original FCS value and length to DSA_TAG_PROTO_BRCM_LEGACY would
impact performance of BCM63xx switches, so it's better to create a new tag.

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Link: https://patch.msgid.link/20250614080000.1884236-3-noltari@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
 include/net/dsa.h  |  2 ++
 net/dsa/Kconfig    | 16 ++++++++--
 net/dsa/tag_brcm.c | 73 +++++++++++++++++++++++++++++++++++++++++++++-
 3 files changed, 88 insertions(+), 3 deletions(-)

--- a/include/net/dsa.h
+++ b/include/net/dsa.h
@@ -54,11 +54,13 @@ struct tc_action;
 #define DSA_TAG_PROTO_RZN1_A5PSW_VALUE		26
 #define DSA_TAG_PROTO_LAN937X_VALUE		27
 #define DSA_TAG_PROTO_VSC73XX_8021Q_VALUE	28
+#define DSA_TAG_PROTO_BRCM_LEGACY_FCS_VALUE	29
 
 enum dsa_tag_protocol {
 	DSA_TAG_PROTO_NONE		= DSA_TAG_PROTO_NONE_VALUE,
 	DSA_TAG_PROTO_BRCM		= DSA_TAG_PROTO_BRCM_VALUE,
 	DSA_TAG_PROTO_BRCM_LEGACY	= DSA_TAG_PROTO_BRCM_LEGACY_VALUE,
+	DSA_TAG_PROTO_BRCM_LEGACY_FCS	= DSA_TAG_PROTO_BRCM_LEGACY_FCS_VALUE,
 	DSA_TAG_PROTO_BRCM_PREPEND	= DSA_TAG_PROTO_BRCM_PREPEND_VALUE,
 	DSA_TAG_PROTO_DSA		= DSA_TAG_PROTO_DSA_VALUE,
 	DSA_TAG_PROTO_EDSA		= DSA_TAG_PROTO_EDSA_VALUE,
--- a/net/dsa/Kconfig
+++ b/net/dsa/Kconfig
@@ -42,12 +42,24 @@ config NET_DSA_TAG_BRCM
 	  Broadcom switches which place the tag after the MAC source address.
 
 config NET_DSA_TAG_BRCM_LEGACY
-	tristate "Tag driver for Broadcom legacy switches using in-frame headers"
+	tristate "Tag driver for BCM63xx legacy switches using in-frame headers"
 	select NET_DSA_TAG_BRCM_COMMON
 	help
 	  Say Y if you want to enable support for tagging frames for the
-	  Broadcom legacy switches which place the tag after the MAC source
+	  BCM63xx legacy switches which place the tag after the MAC source
 	  address.
+	  This tag is used in BCM63xx legacy switches which work without the
+	  original FCS and length before the tag insertion.
+
+config NET_DSA_TAG_BRCM_LEGACY_FCS
+	tristate "Tag driver for BCM53xx legacy switches using in-frame headers"
+	select NET_DSA_TAG_BRCM_COMMON
+	help
+	  Say Y if you want to enable support for tagging frames for the
+	  BCM53xx legacy switches which place the tag after the MAC source
+	  address.
+	  This tag is used in BCM53xx legacy switches which expect original
+	  FCS and length before the tag insertion to be present.
 
 config NET_DSA_TAG_BRCM_PREPEND
 	tristate "Tag driver for Broadcom switches using prepended headers"
--- a/net/dsa/tag_brcm.c
+++ b/net/dsa/tag_brcm.c
@@ -15,6 +15,7 @@
 
 #define BRCM_NAME		"brcm"
 #define BRCM_LEGACY_NAME	"brcm-legacy"
+#define BRCM_LEGACY_FCS_NAME	"brcm-legacy-fcs"
 #define BRCM_PREPEND_NAME	"brcm-prepend"
 
 /* Legacy Broadcom tag (6 bytes) */
@@ -32,6 +33,10 @@
 #define BRCM_LEG_MULTICAST	(1 << 5)
 #define BRCM_LEG_EGRESS		(2 << 5)
 #define BRCM_LEG_INGRESS	(3 << 5)
+#define BRCM_LEG_LEN_HI(x)	(((x) >> 8) & 0x7)
+
+/* 4th byte in the tag */
+#define BRCM_LEG_LEN_LO(x)	((x) & 0xff)
 
 /* 6th byte in the tag */
 #define BRCM_LEG_PORT_ID	(0xf)
@@ -212,7 +217,8 @@ DSA_TAG_DRIVER(brcm_netdev_ops);
 MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_BRCM, BRCM_NAME);
 #endif
 
-#if IS_ENABLED(CONFIG_NET_DSA_TAG_BRCM_LEGACY)
+#if IS_ENABLED(CONFIG_NET_DSA_TAG_BRCM_LEGACY) || \
+	IS_ENABLED(CONFIG_NET_DSA_TAG_BRCM_LEGACY_FCS)
 static struct sk_buff *brcm_leg_tag_rcv(struct sk_buff *skb,
 					struct net_device *dev)
 {
@@ -250,7 +256,9 @@ static struct sk_buff *brcm_leg_tag_rcv(
 
 	return skb;
 }
+#endif /* CONFIG_NET_DSA_TAG_BRCM_LEGACY || CONFIG_NET_DSA_TAG_BRCM_LEGACY_FCS */
 
+#if IS_ENABLED(CONFIG_NET_DSA_TAG_BRCM_LEGACY)
 static struct sk_buff *brcm_leg_tag_xmit(struct sk_buff *skb,
 					 struct net_device *dev)
 {
@@ -300,6 +308,66 @@ DSA_TAG_DRIVER(brcm_legacy_netdev_ops);
 MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_BRCM_LEGACY, BRCM_LEGACY_NAME);
 #endif /* CONFIG_NET_DSA_TAG_BRCM_LEGACY */
 
+#if IS_ENABLED(CONFIG_NET_DSA_TAG_BRCM_LEGACY_FCS)
+static struct sk_buff *brcm_leg_fcs_tag_xmit(struct sk_buff *skb,
+					     struct net_device *dev)
+{
+	struct dsa_port *dp = dsa_user_to_port(dev);
+	unsigned int fcs_len;
+	__le32 fcs_val;
+	u8 *brcm_tag;
+
+	/* The Ethernet switch we are interfaced with needs packets to be at
+	 * least 64 bytes (including FCS) otherwise they will be discarded when
+	 * they enter the switch port logic. When Broadcom tags are enabled, we
+	 * need to make sure that packets are at least 70 bytes (including FCS
+	 * and tag) because the length verification is done after the Broadcom
+	 * tag is stripped off the ingress packet.
+	 *
+	 * Let dsa_user_xmit() free the SKB.
+	 */
+	if (__skb_put_padto(skb, ETH_ZLEN + BRCM_LEG_TAG_LEN, false))
+		return NULL;
+
+	fcs_len = skb->len;
+	fcs_val = cpu_to_le32(crc32_le(~0, skb->data, fcs_len) ^ ~0);
+
+	skb_push(skb, BRCM_LEG_TAG_LEN);
+
+	dsa_alloc_etype_header(skb, BRCM_LEG_TAG_LEN);
+
+	brcm_tag = skb->data + 2 * ETH_ALEN;
+
+	/* Broadcom tag type */
+	brcm_tag[0] = BRCM_LEG_TYPE_HI;
+	brcm_tag[1] = BRCM_LEG_TYPE_LO;
+
+	/* Broadcom tag value */
+	brcm_tag[2] = BRCM_LEG_EGRESS | BRCM_LEG_LEN_HI(fcs_len);
+	brcm_tag[3] = BRCM_LEG_LEN_LO(fcs_len);
+	brcm_tag[4] = 0;
+	brcm_tag[5] = dp->index & BRCM_LEG_PORT_ID;
+
+	/* Original FCS value */
+	if (__skb_pad(skb, ETH_FCS_LEN, false))
+		return NULL;
+	skb_put_data(skb, &fcs_val, ETH_FCS_LEN);
+
+	return skb;
+}
+
+static const struct dsa_device_ops brcm_legacy_fcs_netdev_ops = {
+	.name = BRCM_LEGACY_FCS_NAME,
+	.proto = DSA_TAG_PROTO_BRCM_LEGACY_FCS,
+	.xmit = brcm_leg_fcs_tag_xmit,
+	.rcv = brcm_leg_tag_rcv,
+	.needed_headroom = BRCM_LEG_TAG_LEN,
+};
+
+DSA_TAG_DRIVER(brcm_legacy_fcs_netdev_ops);
+MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_BRCM_LEGACY_FCS, BRCM_LEGACY_FCS_NAME);
+#endif /* CONFIG_NET_DSA_TAG_BRCM_LEGACY_FCS */
+
 #if IS_ENABLED(CONFIG_NET_DSA_TAG_BRCM_PREPEND)
 static struct sk_buff *brcm_tag_xmit_prepend(struct sk_buff *skb,
 					     struct net_device *dev)
@@ -334,6 +402,9 @@ static struct dsa_tag_driver *dsa_tag_dr
 #if IS_ENABLED(CONFIG_NET_DSA_TAG_BRCM_LEGACY)
 	&DSA_TAG_DRIVER_NAME(brcm_legacy_netdev_ops),
 #endif
+#if IS_ENABLED(CONFIG_NET_DSA_TAG_BRCM_LEGACY_FCS)
+	&DSA_TAG_DRIVER_NAME(brcm_legacy_fcs_netdev_ops),
+#endif
 #if IS_ENABLED(CONFIG_NET_DSA_TAG_BRCM_PREPEND)
 	&DSA_TAG_DRIVER_NAME(brcm_prepend_netdev_ops),
 #endif
