ethtool: provide timestamping information with TSINFO_GET request

Implement TSINFO_GET request to get timestamping information for a network
device. This is traditionally available via ETHTOOL_GET_TS_INFO ioctl
request.

Move part of ethtool_get_ts_info() into common.c so that ioctl and netlink
code use the same logic to get timestamping information from the device.

v3: use "TSINFO" rather than "TIMESTAMP", suggested by Richard Cochran

Signed-off-by: Michal Kubecek <mkubecek@suse.cz>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ethtool/common.c

@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0-only
 
 #include <linux/net_tstamp.h>
+#include <linux/phy.h>
 
 #include "common.h"
 
@@ -350,3 +351,23 @@ int ethtool_check_ops(const struct ethtool_ops *ops)
 	 */
 	return 0;
 }
+
+int __ethtool_get_ts_info(struct net_device *dev, struct ethtool_ts_info *info)
+{
+	const struct ethtool_ops *ops = dev->ethtool_ops;
+	struct phy_device *phydev = dev->phydev;
+
+	memset(info, 0, sizeof(*info));
+	info->cmd = ETHTOOL_GET_TS_INFO;
+
+	if (phy_has_tsinfo(phydev))
+		return phy_ts_info(phydev, info);
+	if (ops->get_ts_info)
+		return ops->get_ts_info(dev, info);
+
+	info->so_timestamping = SOF_TIMESTAMPING_RX_SOFTWARE |
+				SOF_TIMESTAMPING_SOFTWARE;
+	info->phc_index = -1;
+
+	return 0;
+}