sfc: extend pedit add action to handle decrement ipv6 hop limit

Extend the pedit add actions to handle this case for ipv6. Similar to ipv4
dec ttl, decrementing ipv6 hop limit can be achieved by adding 0xff to the
hop limit 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>

Author: pieterj-xilinx

drivers/net/ethernet/sfc/tc.c

@@ -1084,6 +1084,31 @@ static int efx_tc_pedit_add(struct efx_nic *efx, struct efx_tc_action_set *act,
 			break;
 		}
 		break;
+	case FLOW_ACT_MANGLE_HDR_TYPE_IP6:
+		switch (fa->mangle.offset) {
+		case round_down(offsetof(struct ipv6hdr, hop_limit), 4):
+			/* check that pedit applies to hoplimit only */
+			if (fa->mangle.mask != EFX_TC_HDR_TYPE_HLIMIT_MASK)
+				break;
+
+			/* Adding 0xff is equivalent to decrementing the hoplimit.
+			 * Other added values are not supported.
+			 */
+			if ((fa->mangle.val >> 24) != U8_MAX)
+				break;
+
+			/* check that we do not decrement hoplimit 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;
 	}