Add support for Motorcomm YT921x tags, which includes a configurable
ethertype field (default to 0x9988).
Signed-off-by: David Yang <mmyangfl@gmail.com>
---
include/net/dsa.h | 2 +
net/dsa/Kconfig | 6 +++
net/dsa/Makefile | 1 +
net/dsa/tag_yt921x.c | 116 +++++++++++++++++++++++++++++++++++++++++++
4 files changed, 125 insertions(+)
create mode 100644 net/dsa/tag_yt921x.c
diff --git a/include/net/dsa.h b/include/net/dsa.h
index d73ea0880066..67762fdaf3c7 100644
--- a/include/net/dsa.h
+++ b/include/net/dsa.h
@@ -55,6 +55,7 @@ struct tc_action;
#define DSA_TAG_PROTO_LAN937X_VALUE 27
#define DSA_TAG_PROTO_VSC73XX_8021Q_VALUE 28
#define DSA_TAG_PROTO_BRCM_LEGACY_FCS_VALUE 29
+#define DSA_TAG_PROTO_YT921X_VALUE 30
enum dsa_tag_protocol {
DSA_TAG_PROTO_NONE = DSA_TAG_PROTO_NONE_VALUE,
@@ -87,6 +88,7 @@ enum dsa_tag_protocol {
DSA_TAG_PROTO_RZN1_A5PSW = DSA_TAG_PROTO_RZN1_A5PSW_VALUE,
DSA_TAG_PROTO_LAN937X = DSA_TAG_PROTO_LAN937X_VALUE,
DSA_TAG_PROTO_VSC73XX_8021Q = DSA_TAG_PROTO_VSC73XX_8021Q_VALUE,
+ DSA_TAG_PROTO_YT921X = DSA_TAG_PROTO_YT921X_VALUE,
};
struct dsa_switch;
diff --git a/net/dsa/Kconfig b/net/dsa/Kconfig
index 869cbe57162f..6b94028b1fcc 100644
--- a/net/dsa/Kconfig
+++ b/net/dsa/Kconfig
@@ -190,4 +190,10 @@ config NET_DSA_TAG_XRS700X
Say Y or M if you want to enable support for tagging frames for
Arrow SpeedChips XRS700x switches that use a single byte tag trailer.
+config NET_DSA_TAG_YT921X
+ tristate "Tag driver for Motorcomm YT921x switches"
+ help
+ Say Y or M if you want to enable support for tagging frames for
+ Motorcomm YT921x switches.
+
endif
diff --git a/net/dsa/Makefile b/net/dsa/Makefile
index 555c07cfeb71..4b011a1d5c87 100644
--- a/net/dsa/Makefile
+++ b/net/dsa/Makefile
@@ -39,6 +39,7 @@ 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_XRS700X) += tag_xrs700x.o
+obj-$(CONFIG_NET_DSA_TAG_YT921X) += tag_yt921x.o
# for tracing framework to find trace.h
CFLAGS_trace.o := -I$(src)
diff --git a/net/dsa/tag_yt921x.c b/net/dsa/tag_yt921x.c
new file mode 100644
index 000000000000..95354bdb0aff
--- /dev/null
+++ b/net/dsa/tag_yt921x.c
@@ -0,0 +1,116 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Motorcomm YT921x Switch External CPU tagging
+ *
+ * Copyright (c) 2025 David Yang <mmyangfl@gmail.com>
+ *
+ * +----+----+-------+-----+----+---------
+ * | DA | SA | TagET | Tag | ET | Payload ...
+ * +----+----+-------+-----+----+---------
+ * 6 6 2 6 2 N
+ *
+ * Tag Ethertype: CPU_TAG_TPID_TPIDf (default: 0x9988)
+ * Tag:
+ * 2: Service VLAN Tag
+ * 2: Rx Port
+ * 15b: Rx Port Valid
+ * 14b-11b: Rx Port
+ * 10b-0b: Unknown Value 0x80
+ * 2: Tx Port(s)
+ * 15b: Tx Port(s) Valid
+ * 10b-0b: Tx Port(s) Mask
+ */
+
+#include <linux/etherdevice.h>
+#include <linux/list.h>
+#include <linux/slab.h>
+
+#include "tag.h"
+
+#define YT921X_NAME "yt921x"
+
+#define YT921X_TAG_LEN 8
+
+#define ETH_P_YT921X 0x9988
+
+#define YT921X_TAG_PORT_ENf BIT(15)
+#define YT921X_TAG_RX_PORTf GENMASK(14, 11)
+#define YT921X_TAG_TX_PORTf GENMASK(10, 0)
+#define YT921X_TAG_TX_PORTnv(port) BIT(port)
+
+static struct sk_buff *
+yt921x_tag_xmit(struct sk_buff *skb, struct net_device *netdev)
+{
+ struct dsa_port *dp = dsa_user_to_port(netdev);
+ __be16 *tag;
+
+ skb_push(skb, YT921X_TAG_LEN);
+ dsa_alloc_etype_header(skb, YT921X_TAG_LEN);
+
+ tag = (__be16 *)(skb->data + 2 * ETH_ALEN);
+
+ /* Might use yt921x_priv::tag_eth_p, but... */
+ tag[0] = htons(ETH_P_YT921X);
+ /* Service VLAN not used here, set to 1 anyway */
+ tag[1] = htons(1);
+ tag[2] = 0;
+ tag[3] = htons(YT921X_TAG_PORT_ENf | YT921X_TAG_TX_PORTnv(dp->index));
+
+ /* Now tell the conduit network device about the desired output queue
+ * as well
+ */
+ skb_set_queue_mapping(skb, dp->index);
+
+ return skb;
+}
+
+static struct sk_buff *
+yt921x_tag_rcv(struct sk_buff *skb, struct net_device *netdev)
+{
+ __be16 *tag;
+ u16 rx;
+ int rx_port;
+
+ if (unlikely(!pskb_may_pull(skb, YT921X_TAG_LEN)))
+ return NULL;
+
+ tag = (__be16 *)skb->data;
+
+ /* Locate which port this is coming from */
+ rx = ntohs(tag[1]);
+ if (unlikely((rx & YT921X_TAG_PORT_ENf) == 0)) {
+ netdev_err(netdev, "Unexpected rx tag 0x%04x\n", rx);
+ return NULL;
+ }
+
+ rx_port = FIELD_GET(YT921X_TAG_RX_PORTf, rx);
+ skb->dev = dsa_conduit_find_user(netdev, 0, rx_port);
+ if (unlikely(!skb->dev)) {
+ dev_warn_ratelimited(&netdev->dev,
+ "Couldn't decode source port\n");
+ return NULL;
+ }
+
+ /* Remove YT921x tag and update checksum */
+ skb_pull_rcsum(skb, YT921X_TAG_LEN);
+
+ dsa_default_offload_fwd_mark(skb);
+
+ dsa_strip_etype_header(skb, YT921X_TAG_LEN);
+
+ return skb;
+}
+
+static const struct dsa_device_ops yt921x_netdev_ops = {
+ .name = YT921X_NAME,
+ .proto = DSA_TAG_PROTO_YT921X,
+ .xmit = yt921x_tag_xmit,
+ .rcv = yt921x_tag_rcv,
+ .needed_headroom = YT921X_TAG_LEN,
+};
+
+MODULE_DESCRIPTION("DSA tag driver for Motorcomm YT921x switches");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_YT921X, YT921X_NAME);
+
+module_dsa_tag_driver(yt921x_netdev_ops);
--
2.47.2On Sat, Aug 09, 2025 at 01:38:02AM +0800, David Yang wrote:
> Add support for Motorcomm YT921x tags, which includes a configurable
> ethertype field (default to 0x9988).
Hi David
Please take a read of:
https://www.kernel.org/doc/html/latest/process/maintainer-netdev.html
We are in the merge window at the moment, so you need to post patches
as RFC. And you need to indicate the tree in the Subject: line.
> +#define YT921X_TAG_PORT_ENf BIT(15)
> +#define YT921X_TAG_RX_PORTf GENMASK(14, 11)
> +#define YT921X_TAG_TX_PORTf GENMASK(10, 0)
> +#define YT921X_TAG_TX_PORTnv(port) BIT(port)
These lower case letters at the end are unusual. What do they
represent?
> +static struct sk_buff *
> +yt921x_tag_xmit(struct sk_buff *skb, struct net_device *netdev)
> +{
> + struct dsa_port *dp = dsa_user_to_port(netdev);
> + __be16 *tag;
> +
> + skb_push(skb, YT921X_TAG_LEN);
> + dsa_alloc_etype_header(skb, YT921X_TAG_LEN);
> +
> + tag = (__be16 *)(skb->data + 2 * ETH_ALEN);
dsa_etype_header_pos_tx() ?
> +static struct sk_buff *
> +yt921x_tag_rcv(struct sk_buff *skb, struct net_device *netdev)
> +{
> + __be16 *tag;
> + u16 rx;
> + int rx_port;
Reverse Christmas tree. Longest to shortest.
Andrew
---
pw-bot: cr
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