[PATCH net-next v2] net: dsa: offer a flowtable to the switch before the conduit

[Julius Bairaktaris <julius@bairaktaris.de>]

A flowtable bound to a DSA user port is forwarded to the conduit netdev
by dsa_user_setup_ft_block(), for a flow engine that sits on the
conduit as mtk_eth's does. It does not go through
ds->ops->port_setup_tc, so a switch that owns its flow engine is never
offered the flowtable.

Offer TC_SETUP_FT to the switch first and forward it to the conduit
only when the switch answers -EOPNOTSUPP. The side that takes the bind
is recorded on the port so that the unbind goes to the same side. Every
in-tree .port_setup_tc returns -EOPNOTSUPP for TC_SETUP_FT, so a
conduit-side flow engine is reached as before.

Assisted-by: Claude:claude-fable-5-1
Signed-off-by: Julius Bairaktaris <julius@bairaktaris.de>
---
v2:
- decide the target on FLOW_BLOCK_BIND and record it on the port, so
  the unbind goes to the side that holds the block callback
- reword the comment
v1: https://lore.kernel.org/netdev/20260901092546.369232-1-julius@bairaktaris.de/

Tested on IPQ8074 with an out-of-tree DSA switch driver that handles
TC_SETUP_FT (openwrt/openwrt#24806): three flowtable unbind/bind cycles,
hardware offload of routed flows after each.

 include/net/dsa.h |  6 ++++++
 net/dsa/user.c    | 25 ++++++++++++++++++++-----
 2 files changed, 26 insertions(+), 5 deletions(-)

diff --git a/include/net/dsa.h b/include/net/dsa.h
index 7507d632e7c6..dbcb02de06fc 100644
--- a/include/net/dsa.h
+++ b/include/net/dsa.h
@@ -297,6 +297,12 @@ struct dsa_port {
 
 	u8			setup:1;
 
+	/* Flowtable blocks on this user port go to the switch, not the
+	 * conduit; decided at bind time. Written without rtnl, so not one of
+	 * the bit fields above.
+	 */
+	bool			ft_on_switch;
+
 	struct device_node	*dn;
 	unsigned int		ageing_time;
 
diff --git a/net/dsa/user.c b/net/dsa/user.c
index 041f9060c8ef..f4cd48df2519 100644
--- a/net/dsa/user.c
+++ b/net/dsa/user.c
@@ -1718,15 +1718,30 @@ static int dsa_user_setup_tc_block(struct net_device *dev,
 	}
 }
 
-static int dsa_user_setup_ft_block(struct dsa_switch *ds, int port,
-				   void *type_data)
+static int dsa_user_setup_ft_block(struct dsa_port *dp,
+				   struct flow_block_offload *bo)
 {
-	struct net_device *conduit = dsa_port_to_conduit(dsa_to_port(ds, port));
+	struct net_device *conduit = dsa_port_to_conduit(dp);
+	struct dsa_switch *ds = dp->ds;
+	int err;
+
+	/* The unbind goes to the side that took the bind. */
+	if (bo->command == FLOW_BLOCK_BIND) {
+		err = -EOPNOTSUPP;
+		if (ds->ops->port_setup_tc)
+			err = ds->ops->port_setup_tc(ds, dp->index, TC_SETUP_FT,
+						     bo);
+		dp->ft_on_switch = err != -EOPNOTSUPP;
+		if (dp->ft_on_switch)
+			return err;
+	} else if (dp->ft_on_switch) {
+		return ds->ops->port_setup_tc(ds, dp->index, TC_SETUP_FT, bo);
+	}
 
 	if (!conduit->netdev_ops->ndo_setup_tc)
 		return -EOPNOTSUPP;
 
-	return conduit->netdev_ops->ndo_setup_tc(conduit, TC_SETUP_FT, type_data);
+	return conduit->netdev_ops->ndo_setup_tc(conduit, TC_SETUP_FT, bo);
 }
 
 static int dsa_user_setup_tc(struct net_device *dev, enum tc_setup_type type,
@@ -1739,7 +1754,7 @@ static int dsa_user_setup_tc(struct net_device *dev, enum tc_setup_type type,
 	case TC_SETUP_BLOCK:
 		return dsa_user_setup_tc_block(dev, type_data);
 	case TC_SETUP_FT:
-		return dsa_user_setup_ft_block(ds, dp->index, type_data);
+		return dsa_user_setup_ft_block(dp, type_data);
 	default:
 		break;
 	}
-- 
2.53.0