mlxsw: spectrum: Don't depend on ip_gre and ip6_gre

mlxsw_spectrum supports offloading of a tc action mirred egress mirror
to a gretap or an ip6gretap netdevice, which necessitates calls to
functions defined in ip_gre, ip6_gre and ip6_tunnel modules. Previously
this was enabled by introducing a hard dependency of MLXSW_SPECTRUM on
NET_IPGRE and IPV6_GRE. However the rest of mlxsw is careful about
picking which modules are absolutely required, and therefore the better
approach is to make mlxsw_spectrum tolerant of absence of one or both of
the GRE flavors.

Hence rework the NET_IPGRE and IPV6_GRE dependencies to just guard
matching modularity, and hide the corresponding code in spectrum_span.c
in an #if IS_ENABLED. Mark mlxsw_sp_span_entry_tunnel_parms_common as
maybe unused, to muffle warnings if neither GRE flavor is selected,
which seems cleaner than introducing a composite #if.

Signed-off-by: Petr Machata <petrm@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlxsw/Kconfig

@@ -76,12 +76,10 @@ config MLXSW_SPECTRUM
 	depends on PSAMPLE || PSAMPLE=n
 	depends on BRIDGE || BRIDGE=n
 	depends on IPV6 || IPV6=n
+	depends on NET_IPGRE || NET_IPGRE=n
+	depends on IPV6_GRE || IPV6_GRE=n
 	select PARMAN
 	select MLXFW
-	depends on NET_IPGRE
-	depends on !(MLXSW_CORE=y && NET_IPGRE=m)
-	depends on IPV6_GRE
-	depends on !(MLXSW_CORE=y && IPV6_GRE=m)
 	default m
 	---help---
 	  This driver supports Mellanox Technologies Spectrum Ethernet

drivers/net/ethernet/mellanox/mlxsw/spectrum_span.c

@@ -167,7 +167,7 @@ mlxsw_sp_span_entry_unoffloadable(struct mlxsw_sp_span_parms *sparmsp)
 	return 0;
 }
 
-static int
+static __maybe_unused int
 mlxsw_sp_span_entry_tunnel_parms_common(struct net_device *l3edev,
 					union mlxsw_sp_l3addr saddr,
 					union mlxsw_sp_l3addr daddr,
@@ -194,6 +194,7 @@ mlxsw_sp_span_entry_tunnel_parms_common(struct net_device *l3edev,
 	return 0;
 }
 
+#if IS_ENABLED(CONFIG_NET_IPGRE)
 static struct net_device *
 mlxsw_sp_span_gretap4_route(const struct net_device *to_dev,
 			    __be32 *saddrp, __be32 *daddrp)
@@ -291,7 +292,9 @@ static const struct mlxsw_sp_span_entry_ops mlxsw_sp_span_entry_ops_gretap4 = {
 	.configure = mlxsw_sp_span_entry_gretap4_configure,
 	.deconfigure = mlxsw_sp_span_entry_gretap4_deconfigure,
 };
+#endif
 
+#if IS_ENABLED(CONFIG_IPV6_GRE)
 static struct net_device *
 mlxsw_sp_span_gretap6_route(const struct net_device *to_dev,
 			    struct in6_addr *saddrp,
@@ -389,12 +392,17 @@ struct mlxsw_sp_span_entry_ops mlxsw_sp_span_entry_ops_gretap6 = {
 	.configure = mlxsw_sp_span_entry_gretap6_configure,
 	.deconfigure = mlxsw_sp_span_entry_gretap6_deconfigure,
 };
+#endif
 
 static const
 struct mlxsw_sp_span_entry_ops *const mlxsw_sp_span_entry_types[] = {
 	&mlxsw_sp_span_entry_ops_phys,
+#if IS_ENABLED(CONFIG_NET_IPGRE)
 	&mlxsw_sp_span_entry_ops_gretap4,
+#endif
+#if IS_ENABLED(CONFIG_IPV6_GRE)
 	&mlxsw_sp_span_entry_ops_gretap6,
+#endif
 };
 
 static int