Debugging certain flows in the offloaded switch data path can be done by
installing two tc-mirred filters for mirroring: one in the hardware data
path, which copies the frames to the CPU, and one which takes the frame
from there and mirrors it to a virtual interface like a dummy device,
where it can be seen with tcpdump.

The effect of having 2 filters run on the same packet can be obtained by
default using tc, by not specifying either the 'skip_sw' or 'skip_hw'
keywords.

Instead of refusing to offload mirroring/redirecting packets towards
interfaces that aren't switch ports, just treat every other destination
for what it is: something that is handled in software, behind the CPU
port.

Usage:

$ ip link add dummy0 type dummy; ip link set dummy0 up
$ tc qdisc add dev swp0 clsact
$ tc filter add dev swp0 ingress protocol ip flower action mirred ingress mirror dev dummy0

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
---
v2->v3: s/f->skip_sw/f->common.skip_sw/
v1->v2: allow mirroring to the ingress of another ocelot port
        (using software)

 drivers/net/ethernet/mscc/ocelot_flower.c | 54 ++++++++++++++++++-----
 1 file changed, 42 insertions(+), 12 deletions(-)

diff --git a/drivers/net/ethernet/mscc/ocelot_flower.c b/drivers/net/ethernet/mscc/ocelot_flower.c
index a057ec3dab97..986b1f150e3b 100644
--- a/drivers/net/ethernet/mscc/ocelot_flower.c
+++ b/drivers/net/ethernet/mscc/ocelot_flower.c
@@ -228,6 +228,32 @@ ocelot_flower_parse_egress_vlan_modify(struct ocelot_vcap_filter *filter,
 	return 0;
 }
 
+static int
+ocelot_flower_parse_egress_port(struct ocelot *ocelot, struct flow_cls_offload *f,
+				const struct flow_action_entry *a, bool mirror,
+				struct netlink_ext_ack *extack)
+{
+	const char *act_string = mirror ? "mirror" : "redirect";
+	int egress_port = ocelot->ops->netdev_to_port(a->dev);
+	enum flow_action_id offloadable_act_id;
+
+	offloadable_act_id = mirror ? FLOW_ACTION_MIRRED : FLOW_ACTION_REDIRECT;
+
+	/* Mirroring towards foreign interfaces is handled in software */
+	if (egress_port < 0 || a->id != offloadable_act_id) {
+		if (f->common.skip_sw) {
+			NL_SET_ERR_MSG_FMT(extack,
+					   "Can only %s to %s if filter also runs in software",
+					   act_string, egress_port < 0 ?
+					   "CPU" : "ingress of ocelot port");
+			return -EOPNOTSUPP;
+		}
+		egress_port = ocelot->num_phys_ports;
+	}
+
+	return egress_port;
+}
+
 static int ocelot_flower_parse_action(struct ocelot *ocelot, int port,
 				      bool ingress, struct flow_cls_offload *f,
 				      struct ocelot_vcap_filter *filter)
@@ -356,6 +382,7 @@ static int ocelot_flower_parse_action(struct ocelot *ocelot, int port,
 			filter->type = OCELOT_VCAP_FILTER_OFFLOAD;
 			break;
 		case FLOW_ACTION_REDIRECT:
+		case FLOW_ACTION_REDIRECT_INGRESS:
 			if (filter->block_id != VCAP_IS2) {
 				NL_SET_ERR_MSG_MOD(extack,
 						   "Redirect action can only be offloaded to VCAP IS2");
@@ -366,17 +393,19 @@ static int ocelot_flower_parse_action(struct ocelot *ocelot, int port,
 						   "Last action must be GOTO");
 				return -EOPNOTSUPP;
 			}
-			egress_port = ocelot->ops->netdev_to_port(a->dev);
-			if (egress_port < 0) {
-				NL_SET_ERR_MSG_MOD(extack,
-						   "Destination not an ocelot port");
-				return -EOPNOTSUPP;
-			}
+
+			egress_port = ocelot_flower_parse_egress_port(ocelot, f,
+								      a, false,
+								      extack);
+			if (egress_port < 0)
+				return egress_port;
+
 			filter->action.mask_mode = OCELOT_MASK_MODE_REDIRECT;
 			filter->action.port_mask = BIT(egress_port);
 			filter->type = OCELOT_VCAP_FILTER_OFFLOAD;
 			break;
 		case FLOW_ACTION_MIRRED:
+		case FLOW_ACTION_MIRRED_INGRESS:
 			if (filter->block_id != VCAP_IS2) {
 				NL_SET_ERR_MSG_MOD(extack,
 						   "Mirror action can only be offloaded to VCAP IS2");
@@ -387,12 +416,13 @@ static int ocelot_flower_parse_action(struct ocelot *ocelot, int port,
 						   "Last action must be GOTO");
 				return -EOPNOTSUPP;
 			}
-			egress_port = ocelot->ops->netdev_to_port(a->dev);
-			if (egress_port < 0) {
-				NL_SET_ERR_MSG_MOD(extack,
-						   "Destination not an ocelot port");
-				return -EOPNOTSUPP;
-			}
+
+			egress_port = ocelot_flower_parse_egress_port(ocelot, f,
+								      a, true,
+								      extack);
+			if (egress_port < 0)
+				return egress_port;
+
 			filter->egress_port.value = egress_port;
 			filter->action.mirror_ena = true;
 			filter->type = OCELOT_VCAP_FILTER_OFFLOAD;
-- 
2.43.0