net: ena: make ena rxfh support ETH_RSS_HASH_NO_CHANGE

As the name suggests ETH_RSS_HASH_NO_CHANGE is received upon changing
the key or indirection table using ethtool while keeping the same hash
function.

Also add a function for retrieving the current hash function from
the ena-com layer.

Fixes: 1738cd3e ("net: ena: Add a driver for Amazon Elastic Network Adapters (ENA)")
Signed-off-by: NSameeh Jubran <sameehj@amazon.com>
Signed-off-by: NSaeed Bshara <saeedb@amazon.com>
Signed-off-by: NArthur Kiyanovski <akiyano@amazon.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/amazon/ena/ena_com.c

@@ -1041,6 +1041,11 @@ static int ena_com_get_feature(struct ena_com_dev *ena_dev,
 				      feature_ver);
 }
 
+int ena_com_get_current_hash_function(struct ena_com_dev *ena_dev)
+{
+	return ena_dev->rss.hash_func;
+}
+
 static void ena_com_hash_key_fill_default_key(struct ena_com_dev *ena_dev)
 {
 	struct ena_admin_feature_rss_flow_hash_control *hash_key =

drivers/net/ethernet/amazon/ena/ena_com.h

@@ -656,6 +656,14 @@ int ena_com_rss_init(struct ena_com_dev *ena_dev, u16 log_size);
  */
 void ena_com_rss_destroy(struct ena_com_dev *ena_dev);
 
+/* ena_com_get_current_hash_function - Get RSS hash function
+ * @ena_dev: ENA communication layer struct
+ *
+ * Return the current hash function.
+ * @return: 0 or one of the ena_admin_hash_functions values.
+ */
+int ena_com_get_current_hash_function(struct ena_com_dev *ena_dev);
+
 /* ena_com_fill_hash_function - Fill RSS hash function
  * @ena_dev: ENA communication layer struct
  * @func: The hash function (Toeplitz or crc)

drivers/net/ethernet/amazon/ena/ena_ethtool.c

@@ -736,6 +736,9 @@ static int ena_set_rxfh(struct net_device *netdev, const u32 *indir,
 	}
 
 	switch (hfunc) {
+	case ETH_RSS_HASH_NO_CHANGE:
+		func = ena_com_get_current_hash_function(ena_dev);
+		break;
 	case ETH_RSS_HASH_TOP:
 		func = ENA_ADMIN_TOEPLITZ;
 		break;