ethtool: Don't check for RXFH fields conflict when no input_xfrm is requested

The requirement of ->get_rxfh_fields() in ethtool_set_rxfh() is there to
verify that we have no conflict of input_xfrm with the RSS fields
options, there is no point in doing it if input_xfrm is not
supported/requested.

This is under the assumption that a driver that supports input_xfrm will
also support ->get_rxfh_fields(), so add a WARN_ON() to
ethtool_check_ops() to verify it, and remove the op NULL check.

This fixes the following error in mlx4_en, which doesn't support
getting/setting RXFH fields.
$ ethtool --set-rxfh-indir eth2 hfunc xor
Cannot set RX flow hash configuration: Operation not supported

Fixes: 7279246 ("net: ethtool: don't mux RXFH via rxnfc callbacks")
Reviewed-by: Dragos Tatulea <[email protected]>
Signed-off-by: Gal Pressman <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: gal-pressman

net/ethtool/common.c

@@ -812,6 +812,8 @@ int ethtool_check_ops(const struct ethtool_ops *ops)
 		return -EINVAL;
 	if (WARN_ON(ops->rxfh_max_num_contexts == 1))
 		return -EINVAL;
+	if (WARN_ON(ops->supported_input_xfrm && !ops->get_rxfh_fields))
+		return -EINVAL;
 	/* NOTE: sufficiently insane drivers may swap ethtool_ops at runtime,
 	 * the fact that ops are checked at registration time does not
 	 * mean the ops attached to a netdev later on are sane.

net/ethtool/ioctl.c

@@ -1041,6 +1041,9 @@ static int ethtool_check_flow_types(struct net_device *dev, u32 input_xfrm)
 	int err;
 	u32 i;
 
+	if (!input_xfrm || input_xfrm == RXH_XFRM_NO_CHANGE)
+		return 0;
+
 	for (i = 0; i < __FLOW_TYPE_COUNT; i++) {
 		struct ethtool_rxfh_fields fields = {
 			.flow_type	= i,
@@ -1523,7 +1526,7 @@ static noinline_for_stack int ethtool_set_rxfh(struct net_device *dev,
 	u8 *rss_config;
 	int ret;
 
-	if (!ops->get_rxnfc || !ops->get_rxfh_fields || !ops->set_rxfh)
+	if (!ops->get_rxnfc || !ops->set_rxfh)
 		return -EOPNOTSUPP;
 
 	if (ops->get_rxfh_indir_size)