sfc: Document conditions for multicast replication vs filter replacement

Add the efx_filter_is_mc_recip() function to decide whether a filter
is for a multicast recipient and can coexist with other filters with
the same match values.  Update efx_filter_insert_filter() kernel-doc
to explain the conditions for this.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>

1 files changed, 34 insertions, 0 deletions

diff --git a/drivers/net/ethernet/sfc/rx.c b/drivers/net/ethernet/sfc/rx.c
index 864b6ffc9cb2..81eab21effe9 100644
--- a/drivers/net/ethernet/sfc/rx.c
+++ b/drivers/net/ethernet/sfc/rx.c
@@ -903,3 +903,37 @@ bool __efx_filter_rfs_expire(struct efx_nic *efx, unsigned int quota)
 }
 
 #endif /* CONFIG_RFS_ACCEL */
+
+/**
+ * efx_filter_is_mc_recipient - test whether spec is a multicast recipient
+ * @spec: Specification to test
+ *
+ * Return: %true if the specification is a non-drop RX filter that
+ * matches a local MAC address I/G bit value of 1 or matches a local
+ * IPv4 or IPv6 address value in the respective multicast address
+ * range.  Otherwise %false.
+ */
+bool efx_filter_is_mc_recipient(const struct efx_filter_spec *spec)
+{
+	if (!(spec->flags & EFX_FILTER_FLAG_RX) ||
+	    spec->dmaq_id == EFX_FILTER_RX_DMAQ_ID_DROP)
+		return false;
+
+	if (spec->match_flags &
+	    (EFX_FILTER_MATCH_LOC_MAC | EFX_FILTER_MATCH_LOC_MAC_IG) &&
+	    is_multicast_ether_addr(spec->loc_mac))
+		return true;
+
+	if ((spec->match_flags &
+	     (EFX_FILTER_MATCH_ETHER_TYPE | EFX_FILTER_MATCH_LOC_HOST)) ==
+	    (EFX_FILTER_MATCH_ETHER_TYPE | EFX_FILTER_MATCH_LOC_HOST)) {
+		if (spec->ether_type == htons(ETH_P_IP) &&
+		    ipv4_is_multicast(spec->loc_host[0]))
+			return true;
+		if (spec->ether_type == htons(ETH_P_IPV6) &&
+		    ((const u8 *)spec->loc_host)[0] == 0xff)
+			return true;
+	}
+
+	return false;
+}