sfc: introduce pedit add actions on the ipv4 ttl field

Introduce pedit add actions and use it to achieve decrement ttl offload.
Decrement ttl can be achieved by adding 0xff to the ttl field.
Co-developed-by: Edward Cree <ecree.xilinx@gmail.com>
Signed-off-by: Edward Cree <ecree.xilinx@gmail.com>
Signed-off-by: Pieter Jansen van Vuuren <pieter.jansen-van-vuuren@amd.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/sfc/tc.c

@@ -1054,6 +1054,47 @@ static int efx_tc_complete_mac_mangle(struct efx_nic *efx,
 	return 0;
 }
 
+static int efx_tc_pedit_add(struct efx_nic *efx, struct efx_tc_action_set *act,
+			    const struct flow_action_entry *fa,
+			    struct netlink_ext_ack *extack)
+{
+	switch (fa->mangle.htype) {
+	case FLOW_ACT_MANGLE_HDR_TYPE_IP4:
+		switch (fa->mangle.offset) {
+		case offsetof(struct iphdr, ttl):
+			/* check that pedit applies to ttl only */
+			if (fa->mangle.mask != ~EFX_TC_HDR_TYPE_TTL_MASK)
+				break;
+
+			/* Adding 0xff is equivalent to decrementing the ttl.
+			 * Other added values are not supported.
+			 */
+			if ((fa->mangle.val & EFX_TC_HDR_TYPE_TTL_MASK) != U8_MAX)
+				break;
+
+			/* check that we do not decrement ttl twice */
+			if (!efx_tc_flower_action_order_ok(act,
+							   EFX_TC_AO_DEC_TTL)) {
+				NL_SET_ERR_MSG_MOD(extack, "Unsupported: multiple dec ttl");
+				return -EOPNOTSUPP;
+			}
+			act->do_ttl_dec = 1;
+			return 0;
+		default:
+			break;
+		}
+		break;
+	default:
+		break;
+	}
+
+	NL_SET_ERR_MSG_FMT_MOD(extack,
+			       "Unsupported: ttl add action type %x %x %x/%x",
+			       fa->mangle.htype, fa->mangle.offset,
+			       fa->mangle.val, fa->mangle.mask);
+	return -EOPNOTSUPP;
+}
+
 /**
  * efx_tc_mangle() - handle a single 32-bit (or less) pedit
  * @efx:	NIC we're installing a flow rule on
@@ -2014,6 +2055,11 @@ static int efx_tc_flower_replace(struct efx_nic *efx,
 			act->vlan_proto[act->vlan_push] = fa->vlan.proto;
 			act->vlan_push++;
 			break;
+		case FLOW_ACTION_ADD:
+			rc = efx_tc_pedit_add(efx, act, fa, extack);
+			if (rc < 0)
+				goto release;
+			break;
 		case FLOW_ACTION_MANGLE:
 			rc = efx_tc_mangle(efx, act, fa, &mung, extack, &match);
 			if (rc < 0)