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>
diff --git a/net/ethtool/ioctl.c b/net/ethtool/ioctl.c
index 05a2bf6..89d0b18 100644
--- a/net/ethtool/ioctl.c
+++ b/net/ethtool/ioctl.c
@@ -2140,32 +2140,17 @@ static int ethtool_get_dump_data(struct net_device *dev,
 
 static int ethtool_get_ts_info(struct net_device *dev, void __user *useraddr)
 {
-	int err = 0;
 	struct ethtool_ts_info info;
-	const struct ethtool_ops *ops = dev->ethtool_ops;
-	struct phy_device *phydev = dev->phydev;
+	int err;
 
-	memset(&info, 0, sizeof(info));
-	info.cmd = ETHTOOL_GET_TS_INFO;
-
-	if (phy_has_tsinfo(phydev)) {
-		err = phy_ts_info(phydev, &info);
-	} else if (ops->get_ts_info) {
-		err = ops->get_ts_info(dev, &info);
-	} else {
-		info.so_timestamping =
-			SOF_TIMESTAMPING_RX_SOFTWARE |
-			SOF_TIMESTAMPING_SOFTWARE;
-		info.phc_index = -1;
-	}
-
+	err = __ethtool_get_ts_info(dev, &info);
 	if (err)
 		return err;
 
 	if (copy_to_user(useraddr, &info, sizeof(info)))
-		err = -EFAULT;
+		return -EFAULT;
 
-	return err;
+	return 0;
 }
 
 static int __ethtool_get_module_info(struct net_device *dev,