Add offloading for packet duplication supported by the YT921x switches.

Signed-off-by: David Yang <mmyangfl@gmail.com>
---
 drivers/net/dsa/yt921x.c | 24 ++++++++++++++++++++++++
 net/dsa/tag_yt921x.c     |  4 ++++
 2 files changed, 28 insertions(+)

diff --git a/drivers/net/dsa/yt921x.c b/drivers/net/dsa/yt921x.c
index e88b4037ee80..e7b416719b58 100644
--- a/drivers/net/dsa/yt921x.c
+++ b/drivers/net/dsa/yt921x.c
@@ -1038,6 +1038,27 @@ static int yt921x_dsa_port_max_mtu(struct dsa_switch *ds, int port)
 	return YT921X_FRAME_SIZE_MAX - ETH_HLEN - ETH_FCS_LEN - YT921X_TAG_LEN;
 }
 
+static int
+yt921x_dsa_port_hsr_leave(struct dsa_switch *ds, int port,
+			  struct net_device *hsr)
+{
+	return 0;
+}
+
+static int
+yt921x_dsa_port_hsr_join(struct dsa_switch *ds, int port,
+			 struct net_device *hsr, struct netlink_ext_ack *extack)
+{
+	struct dsa_port *dp = dsa_to_port(ds, port);
+	struct net_device *user = dp->user;
+
+	/* Nothing special here; we natively support tx packet duplication */
+
+	user->features |= NETIF_F_HW_HSR_DUP;
+
+	return 0;
+}
+
 static int
 yt921x_mirror_del(struct yt921x_priv *priv, int port, bool ingress)
 {
@@ -2880,6 +2901,9 @@ static const struct dsa_switch_ops yt921x_dsa_switch_ops = {
 	/* mtu */
 	.port_change_mtu	= yt921x_dsa_port_change_mtu,
 	.port_max_mtu		= yt921x_dsa_port_max_mtu,
+	/* hsr */
+	.port_hsr_leave		= yt921x_dsa_port_hsr_leave,
+	.port_hsr_join		= yt921x_dsa_port_hsr_join,
 	/* mirror */
 	.port_mirror_del	= yt921x_dsa_port_mirror_del,
 	.port_mirror_add	= yt921x_dsa_port_mirror_add,
diff --git a/net/dsa/tag_yt921x.c b/net/dsa/tag_yt921x.c
index 995da44f0a2a..0ad83924fda1 100644
--- a/net/dsa/tag_yt921x.c
+++ b/net/dsa/tag_yt921x.c
@@ -46,6 +46,7 @@ yt921x_tag_xmit(struct sk_buff *skb, struct net_device *netdev)
 {
 	struct dsa_port *dp = dsa_user_to_port(netdev);
 	unsigned int port = dp->index;
+	struct dsa_port *partner;
 	__be16 *tag;
 	u16 tx;
 
@@ -59,6 +60,9 @@ yt921x_tag_xmit(struct sk_buff *skb, struct net_device *netdev)
 	tag[1] = 0;
 	tag[2] = 0;
 	tx = YT921X_TAG_PORT_EN | YT921X_TAG_TX_PORTn(port);
+	if (dp->hsr_dev)
+		dsa_hsr_foreach_port(partner, dp->ds, dp->hsr_dev)
+			tx |= YT921X_TAG_TX_PORTn(partner->index);
 	tag[3] = htons(tx);
 
 	return skb;
-- 
2.51.0

On Wed, Nov 26, 2025 at 05:32:36PM +0800, David Yang wrote:
> Add offloading for packet duplication supported by the YT921x switches.
> 
> Signed-off-by: David Yang <mmyangfl@gmail.com>
> ---

I like the idea behind this patch from a purely technical perspective,
but there's an important question. Do you, or people you know or have
interacted with, use HSR/PRP on the YT921x switches, in order to find
this change useful?

If NETIF_F_HW_HSR_DUP is the only offload that the switch supports, then
one can hardly say that the switch was designed to be an HSR accelerator.
I'm working on some patches to make this feature generically available
to most DSA switch drivers, rather than being arbitrarily implemented
here and there. The usefulness of having this single offload generally
available is where I am lacking some data points.