net: ethernet: Add net_eth_get_ptp_clock_by_index() function

This can be used to get the PTP clock if only network interface
index is known.

Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>

include/net/ethernet.h

@@ -682,6 +682,26 @@ static inline struct device *net_eth_get_ptp_clock(struct net_if *iface)
 }
 #endif
 
+/**
+ * @brief Return PTP clock that is tied to this ethernet network interface
+ * index.
+ *
+ * @param index Network interface index
+ *
+ * @return Pointer to PTP clock if found, NULL if not found or if this
+ * ethernet interface index does not support PTP.
+ */
+#if defined(CONFIG_PTP_CLOCK)
+struct device *net_eth_get_ptp_clock_by_index(int index);
+#else
+static inline struct device *net_eth_get_ptp_clock_by_index(int index)
+{
+	ARG_UNUSED(index);
+
+	return NULL;
+}
+#endif
+
 /**
  * @brief Return gPTP port number attached to this interface.
  *

subsys/net/l2/ethernet/ethernet.c

@@ -987,6 +987,20 @@ struct device *net_eth_get_ptp_clock(struct net_if *iface)
 }
 #endif /* CONFIG_PTP_CLOCK */
 
+#if defined(CONFIG_PTP_CLOCK)
+struct device *net_eth_get_ptp_clock_by_index(int index)
+{
+	struct net_if *iface;
+
+	iface = net_if_get_by_index(index);
+	if (!iface) {
+		return NULL;
+	}
+
+	return net_eth_get_ptp_clock(iface);
+}
+#endif
+
 #if defined(CONFIG_NET_GPTP)
 int net_eth_get_ptp_port(struct net_if *iface)
 {