ethtool: Add kernel API for PHC index

Add a new function, which returns the physical clock index of a
networking device. This function will be used to get the physical clock
of a device for timestamp manipulation in the receive path.

Signed-off-by: Gerhard Engleder <gerhard@engleder-embedded.com>

include/linux/ethtool.h

@@ -820,6 +820,14 @@ void
 ethtool_params_from_link_mode(struct ethtool_link_ksettings *link_ksettings,
 			      enum ethtool_link_mode_bit_indices link_mode);
 
+/**
+ * ethtool_get_phc - Get phc index
+ * @dev: pointer to net_device structure
+ *
+ * Return index of phc
+ */
+int ethtool_get_phc(struct net_device *dev);
+
 /**
  * ethtool_get_phc_vclocks - Derive phc vclocks information, and caller
  *                           is responsible to free memory of vclock_index

net/ethtool/common.c

@@ -557,6 +557,19 @@ int __ethtool_get_ts_info(struct net_device *dev, struct ethtool_ts_info *info)
 	return 0;
 }
 
+int ethtool_get_phc(struct net_device *dev)
+{
+	struct ethtool_ts_info info;
+	int ret;
+
+	ret = __ethtool_get_ts_info(dev, &info);
+	if (ret)
+		return ret;
+
+	return info.phc_index;
+}
+EXPORT_SYMBOL(ethtool_get_phc);
+
 int ethtool_get_phc_vclocks(struct net_device *dev, int **vclock_index)
 {
 	struct ethtool_ts_info info = { };