[PATCH net-next v2 0/3] net: dsa: brcm: add legacy FCS tag

[PATCH net-next v2 0/3] net: dsa: brcm: add legacy FCS tag

[Álvaro Fernández Rojas]

The existing brcm legacy tag only works with BCM63xx switches.
These patches add a new legacy tag for BCM5325 and BCM5365 switches, which
require including the FCS and length.

Álvaro Fernández Rojas (3):
  net: dsa: tag_brcm: legacy: reorganize functions
  net: dsa: tag_brcm: add support for legacy FCS tags
  net: dsa: b53: support legacy FCS tags

 v2: replace swab32 with cpu_to_le32.

 drivers/net/dsa/b53/Kconfig      |   1 +
 drivers/net/dsa/b53/b53_common.c |   7 +-
 include/net/dsa.h                |   2 +
 net/dsa/Kconfig                  |   8 +++
 net/dsa/tag_brcm.c               | 119 ++++++++++++++++++++++++-------
 5 files changed, 111 insertions(+), 26 deletions(-)

-- 
2.39.5

[PATCH net-next v2 1/3] net: dsa: tag_brcm: legacy: reorganize functions

[Álvaro Fernández Rojas]

Move brcm_leg_tag_rcv() definition to top.
This function is going to be shared between two different tags.

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
---
 net/dsa/tag_brcm.c | 64 +++++++++++++++++++++++-----------------------
 1 file changed, 32 insertions(+), 32 deletions(-)

 v2: no changes

diff --git a/net/dsa/tag_brcm.c b/net/dsa/tag_brcm.c
index fe75821623a4f..9f4b0bcd95cde 100644
--- a/net/dsa/tag_brcm.c
+++ b/net/dsa/tag_brcm.c
@@ -213,6 +213,38 @@ MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_BRCM, BRCM_NAME);
 #endif
 
 #if IS_ENABLED(CONFIG_NET_DSA_TAG_BRCM_LEGACY)
+static struct sk_buff *brcm_leg_tag_rcv(struct sk_buff *skb,
+					struct net_device *dev)
+{
+	int len = BRCM_LEG_TAG_LEN;
+	int source_port;
+	u8 *brcm_tag;
+
+	if (unlikely(!pskb_may_pull(skb, BRCM_LEG_TAG_LEN + VLAN_HLEN)))
+		return NULL;
+
+	brcm_tag = dsa_etype_header_pos_rx(skb);
+
+	source_port = brcm_tag[5] & BRCM_LEG_PORT_ID;
+
+	skb->dev = dsa_conduit_find_user(dev, 0, source_port);
+	if (!skb->dev)
+		return NULL;
+
+	/* VLAN tag is added by BCM63xx internal switch */
+	if (netdev_uses_dsa(skb->dev))
+		len += VLAN_HLEN;
+
+	/* Remove Broadcom tag and update checksum */
+	skb_pull_rcsum(skb, len);
+
+	dsa_default_offload_fwd_mark(skb);
+
+	dsa_strip_etype_header(skb, len);
+
+	return skb;
+}
+
 static struct sk_buff *brcm_leg_tag_xmit(struct sk_buff *skb,
 					 struct net_device *dev)
 {
@@ -250,38 +282,6 @@ static struct sk_buff *brcm_leg_tag_xmit(struct sk_buff *skb,
 	return skb;
 }
 
-static struct sk_buff *brcm_leg_tag_rcv(struct sk_buff *skb,
-					struct net_device *dev)
-{
-	int len = BRCM_LEG_TAG_LEN;
-	int source_port;
-	u8 *brcm_tag;
-
-	if (unlikely(!pskb_may_pull(skb, BRCM_LEG_TAG_LEN + VLAN_HLEN)))
-		return NULL;
-
-	brcm_tag = dsa_etype_header_pos_rx(skb);
-
-	source_port = brcm_tag[5] & BRCM_LEG_PORT_ID;
-
-	skb->dev = dsa_conduit_find_user(dev, 0, source_port);
-	if (!skb->dev)
-		return NULL;
-
-	/* VLAN tag is added by BCM63xx internal switch */
-	if (netdev_uses_dsa(skb->dev))
-		len += VLAN_HLEN;
-
-	/* Remove Broadcom tag and update checksum */
-	skb_pull_rcsum(skb, len);
-
-	dsa_default_offload_fwd_mark(skb);
-
-	dsa_strip_etype_header(skb, len);
-
-	return skb;
-}
-
 static const struct dsa_device_ops brcm_legacy_netdev_ops = {
 	.name = BRCM_LEGACY_NAME,
 	.proto = DSA_TAG_PROTO_BRCM_LEGACY,
-- 
2.39.5

[PATCH net-next v2 2/3] net: dsa: tag_brcm: add support for legacy FCS tags

[Álvaro Fernández Rojas]

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>
---
 include/net/dsa.h  |  2 ++
 net/dsa/Kconfig    |  8 +++++
 net/dsa/tag_brcm.c | 73 +++++++++++++++++++++++++++++++++++++++++++++-
 3 files changed, 82 insertions(+), 1 deletion(-)

 v2: replace swab32 with cpu_to_le32.

diff --git a/include/net/dsa.h b/include/net/dsa.h
index 55e2d97f247eb..d73ea08800660 100644
--- 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,
diff --git a/net/dsa/Kconfig b/net/dsa/Kconfig
index 2dfe9063613fe..e6696e8212cf3 100644
--- a/net/dsa/Kconfig
+++ b/net/dsa/Kconfig
@@ -49,6 +49,14 @@ config NET_DSA_TAG_BRCM_LEGACY
 	  Broadcom legacy switches which place the tag after the MAC source
 	  address.
 
+config NET_DSA_TAG_BRCM_LEGACY_FCS
+	tristate "Tag driver for Broadcom legacy switches using in-frame headers, FCS and length"
+	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
+	  address and require the original FCS and length.
+
 config NET_DSA_TAG_BRCM_PREPEND
 	tristate "Tag driver for Broadcom switches using prepended headers"
 	select NET_DSA_TAG_BRCM_COMMON
diff --git a/net/dsa/tag_brcm.c b/net/dsa/tag_brcm.c
index 9f4b0bcd95cde..fff05ed3318f7 100644
--- 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)
 {
@@ -244,7 +250,9 @@ static struct sk_buff *brcm_leg_tag_rcv(struct sk_buff *skb,
 
 	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)
 {
@@ -294,6 +302,66 @@ 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;
+	u32 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(~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)
@@ -328,6 +396,9 @@ static struct dsa_tag_driver *dsa_tag_driver_array[] =	{
 #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
-- 
2.39.5

[PATCH net-next v2 3/3] net: dsa: b53: support legacy FCS tags

[Álvaro Fernández Rojas]

Commit 46c5176c586c ("net: dsa: b53: support legacy tags") introduced
support for legacy tags, but it turns out that BCM5325 and BCM5365
switches require the original FCS value and length, so they have to be
treated differently.

Fixes: 46c5176c586c ("net: dsa: b53: support legacy tags")
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
---
 drivers/net/dsa/b53/Kconfig      | 1 +
 drivers/net/dsa/b53/b53_common.c | 7 +++++--
 2 files changed, 6 insertions(+), 2 deletions(-)

 v2: no changes

diff --git a/drivers/net/dsa/b53/Kconfig b/drivers/net/dsa/b53/Kconfig
index ebaa4a80d5444..915008e8eff53 100644
--- a/drivers/net/dsa/b53/Kconfig
+++ b/drivers/net/dsa/b53/Kconfig
@@ -5,6 +5,7 @@ menuconfig B53
 	select NET_DSA_TAG_NONE
 	select NET_DSA_TAG_BRCM
 	select NET_DSA_TAG_BRCM_LEGACY
+	select NET_DSA_TAG_BRCM_LEGACY_FCS
 	select NET_DSA_TAG_BRCM_PREPEND
 	help
 	  This driver adds support for Broadcom managed switch chips. It supports
diff --git a/drivers/net/dsa/b53/b53_common.c b/drivers/net/dsa/b53/b53_common.c
index 862bdccb74397..222107223d109 100644
--- a/drivers/net/dsa/b53/b53_common.c
+++ b/drivers/net/dsa/b53/b53_common.c
@@ -2245,8 +2245,11 @@ enum dsa_tag_protocol b53_get_tag_protocol(struct dsa_switch *ds, int port,
 		goto out;
 	}
 
-	/* Older models require a different 6 byte tag */
-	if (is5325(dev) || is5365(dev) || is63xx(dev)) {
+	/* Older models require different 6 byte tags */
+	if (is5325(dev) || is5365(dev)) {
+		dev->tag_protocol = DSA_TAG_PROTO_BRCM_LEGACY_FCS;
+		goto out;
+	} else if (is63xx(dev)) {
 		dev->tag_protocol = DSA_TAG_PROTO_BRCM_LEGACY;
 		goto out;
 	}
-- 
2.39.5

Re: [PATCH net-next v2 1/3] net: dsa: tag_brcm: legacy: reorganize functions

[Florian Fainelli]

On 6/10/25 09:31, Álvaro Fernández Rojas wrote:
> Move brcm_leg_tag_rcv() definition to top.
> This function is going to be shared between two different tags.
> 
> Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>

Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
-- 
Florian

Re: [PATCH net-next v2 3/3] net: dsa: b53: support legacy FCS tags

[Florian Fainelli]

On 6/10/25 09:31, Álvaro Fernández Rojas wrote:
> Commit 46c5176c586c ("net: dsa: b53: support legacy tags") introduced
> support for legacy tags, but it turns out that BCM5325 and BCM5365
> switches require the original FCS value and length, so they have to be
> treated differently.
> 
> Fixes: 46c5176c586c ("net: dsa: b53: support legacy tags")
> Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>

Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
-- 
Florian

Re: [PATCH net-next v2 2/3] net: dsa: tag_brcm: add support for legacy FCS tags

[Jakub Kicinski]

On Tue, 10 Jun 2025 18:31:53 +0200 Álvaro Fernández Rojas wrote:
> +	struct dsa_port *dp = dsa_user_to_port(dev);
> +	unsigned int fcs_len;
> +	u32 fcs_val;
> +	u8 *brcm_tag;

nit: please reorder the variable declaration lines longest to shortest

> +	/* 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(~0, skb->data, fcs_len) ^ ~0);

sparse (C=1 build flag) complains about the loss of type annotation:

net/dsa/tag_brcm.c:327:17: warning: incorrect type in assignment (different base types)
net/dsa/tag_brcm.c:327:17:    expected unsigned int [usertype] fcs_val
net/dsa/tag_brcm.c:327:17:    got restricted __le32 [usertype]

> +	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);
-- 
pw-bot: cr