ethtool: Add a common function for drivers with transmit time stamping.

Currently, most drivers do not support transmit SO_TIMESTAMPING. For those
that do support it, there is one appropriate response to the get_ts_info
query. This patch adds a common function providing this response.
Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Reviewed-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/ethtool.h

@@ -811,6 +811,7 @@ struct net_device;
 
 /* Some generic methods drivers may use in their ethtool_ops */
 u32 ethtool_op_get_link(struct net_device *dev);
+int ethtool_op_get_ts_info(struct net_device *dev, struct ethtool_ts_info *eti);
 
 /**
  * ethtool_rxfh_indir_default - get default value for RX flow hash indirection

net/core/ethtool.c

@@ -38,6 +38,17 @@ u32 ethtool_op_get_link(struct net_device *dev)
 }
 EXPORT_SYMBOL(ethtool_op_get_link);
 
+int ethtool_op_get_ts_info(struct net_device *dev, struct ethtool_ts_info *info)
+{
+	info->so_timestamping =
+		SOF_TIMESTAMPING_TX_SOFTWARE |
+		SOF_TIMESTAMPING_RX_SOFTWARE |
+		SOF_TIMESTAMPING_SOFTWARE;
+	info->phc_index = -1;
+	return 0;
+}
+EXPORT_SYMBOL(ethtool_op_get_ts_info);
+
 /* Handlers for each ethtool command */
 
 #define ETHTOOL_DEV_FEATURE_WORDS	((NETDEV_FEATURE_COUNT + 31) / 32)