sfc: add decrement ipv6 hop limit by offloading set hop limit actions

Offload pedit set ipv6 hop limit, where the hop limit has already been
matched and the new value is one less, by translating it to a decrement.

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

@@ -32,6 +32,8 @@ enum efx_encap_type efx_tc_indr_netdev_type(struct net_device *net_dev)
 }
 
 #define EFX_TC_HDR_TYPE_TTL_MASK ((u32)0xff)
+/* Hoplimit is stored in the most significant byte in the pedit ipv6 header action */
+#define EFX_TC_HDR_TYPE_HLIMIT_MASK ~((u32)0xff000000)
 #define EFX_EFV_PF	NULL
 /* Look up the representor information (efv) for a device.
  * May return NULL for the PF (us), or an error pointer for a device that
@@ -1190,6 +1192,63 @@ static int efx_tc_mangle(struct efx_nic *efx, struct efx_tc_action_set *act,
 			return -EOPNOTSUPP;
 		}
 		break;
+	case FLOW_ACT_MANGLE_HDR_TYPE_IP6:
+		switch (fa->mangle.offset) {
+		case round_down(offsetof(struct ipv6hdr, hop_limit), 4):
+			/* we currently only support pedit IP6 when it applies
+			 * to the hoplimit and then only when it can be achieved
+			 * with a decrement hoplimit action
+			 */
+
+			/* check that pedit applies to ttl only */
+			if (fa->mangle.mask != EFX_TC_HDR_TYPE_HLIMIT_MASK) {
+				NL_SET_ERR_MSG_FMT_MOD(extack,
+						       "Unsupported: mask (%#x) out of range, only support mangle action on ipv6.hop_limit",
+						       fa->mangle.mask);
+
+				return -EOPNOTSUPP;
+			}
+
+			/* we can only convert to a dec ttl when we have an
+			 * exact match on the ttl field
+			 */
+			if (match->mask.ip_ttl != U8_MAX) {
+				NL_SET_ERR_MSG_FMT_MOD(extack,
+						       "Unsupported: only support mangle ipv6.hop_limit when we have an exact match on ttl, mask used for match (%#x)",
+						       match->mask.ip_ttl);
+				return -EOPNOTSUPP;
+			}
+
+			/* check that we don't try to decrement 0, which equates
+			 * to setting the ttl to 0xff
+			 */
+			if (match->value.ip_ttl == 0) {
+				NL_SET_ERR_MSG_MOD(extack,
+						   "Unsupported: we cannot decrement hop_limit past 0");
+				return -EOPNOTSUPP;
+			}
+
+			/* 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;
+			}
+
+			/* check pedit can be achieved with decrement action */
+			tr_ttl = match->value.ip_ttl - 1;
+			if ((fa->mangle.val >> 24) == tr_ttl) {
+				act->do_ttl_dec = 1;
+				return 0;
+			}
+
+			fallthrough;
+		default:
+			NL_SET_ERR_MSG_FMT_MOD(extack,
+					       "Unsupported: only support mangle on the hop_limit field");
+			return -EOPNOTSUPP;
+		}
 	default:
 		NL_SET_ERR_MSG_FMT_MOD(extack, "Unhandled mangle htype %u for action rule",
 				       fa->mangle.htype);