net: stmmac: Add support for external trigger timestamping

The Synopsis MAC controller supports auxiliary snapshot feature that
allows user to store a snapshot of the system time based on an external
event.

This patch add supports to the above mentioned feature. Users will be
able to triggered capturing the time snapshot from user-space using
application such as testptp or any other applications that uses the
PTP_EXTTS_REQUEST ioctl request.

Cc: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: Tan Tee Min <tee.min.tan@intel.com>
Co-developed-by: Wong Vee Khee <vee.khee.wong@linux.intel.com>
Signed-off-by: Wong Vee Khee <vee.khee.wong@linux.intel.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac.h b/drivers/net/ethernet/stmicro/stmmac/stmmac.h
index b8a4226..b6cd43e 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac.h
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac.h
@@ -250,6 +250,9 @@ struct stmmac_priv {
 	int use_riwt;
 	int irq_wake;
 	spinlock_t ptp_lock;
+	/* Protects auxiliary snapshot registers from concurrent access. */
+	struct mutex aux_ts_lock;
+
 	void __iomem *mmcaddr;
 	void __iomem *ptpaddr;
 	unsigned long active_vlans[BITS_TO_LONGS(VLAN_N_VID)];