can: dev: add generic function can_eth_ioctl_hwts()

Tools based on libpcap (such as tcpdump) expect the SIOCSHWTSTAMP
ioctl call to be supported. This is also specified in the kernel doc
[1]. The purpose of this ioctl is to toggle the hardware timestamps.

Currently, CAN devices which support hardware timestamping have those
always activated. can_eth_ioctl_hwts() is a dumb function that will
always succeed when requested to set tx_type to HWTSTAMP_TX_ON or
rx_filter to HWTSTAMP_FILTER_ALL.

[1] Kernel doc: Timestamping, section 3.1 "Hardware Timestamping
Implementation: Device Drivers"
Link: https://docs.kernel.org/networking/timestamping.html#hardware-timestamping-implementation-device-driversSigned-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Link: https://lore.kernel.org/all/20220727101641.198847-9-mailhol.vincent@wanadoo.frSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/dev/dev.c

@@ -322,6 +322,35 @@ int can_change_mtu(struct net_device *dev, int new_mtu)
 }
 EXPORT_SYMBOL_GPL(can_change_mtu);
 
+/* generic implementation of netdev_ops::ndo_eth_ioctl for CAN devices
+ * supporting hardware timestamps
+ */
+int can_eth_ioctl_hwts(struct net_device *netdev, struct ifreq *ifr, int cmd)
+{
+	struct hwtstamp_config hwts_cfg = { 0 };
+
+	switch (cmd) {
+	case SIOCSHWTSTAMP: /* set */
+		if (copy_from_user(&hwts_cfg, ifr->ifr_data, sizeof(hwts_cfg)))
+			return -EFAULT;
+		if (hwts_cfg.tx_type == HWTSTAMP_TX_ON &&
+		    hwts_cfg.rx_filter == HWTSTAMP_FILTER_ALL)
+			return 0;
+		return -ERANGE;
+
+	case SIOCGHWTSTAMP: /* get */
+		hwts_cfg.tx_type = HWTSTAMP_TX_ON;
+		hwts_cfg.rx_filter = HWTSTAMP_FILTER_ALL;
+		if (copy_to_user(ifr->ifr_data, &hwts_cfg, sizeof(hwts_cfg)))
+			return -EFAULT;
+		return 0;
+
+	default:
+		return -EOPNOTSUPP;
+	}
+}
+EXPORT_SYMBOL(can_eth_ioctl_hwts);
+
 /* generic implementation of ethtool_ops::get_ts_info for CAN devices
  * supporting hardware timestamps
  */

include/linux/can/dev.h

@@ -163,6 +163,7 @@ struct can_priv *safe_candev_priv(struct net_device *dev);
 int open_candev(struct net_device *dev);
 void close_candev(struct net_device *dev);
 int can_change_mtu(struct net_device *dev, int new_mtu);
+int can_eth_ioctl_hwts(struct net_device *netdev, struct ifreq *ifr, int cmd);
 int can_ethtool_op_get_ts_info_hwts(struct net_device *dev,
 				    struct ethtool_ts_info *info);