can: c_can: add ethtool support

With commit 132f2d45fb23 ("can: c_can: add support to 64 message
objects") the number of message objects used for reception /
transmission depends on FIFO size.

The ethtools API support allows you to retrieve this info. Driver info
has been added too.

Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Dario Binacchi <[e-mail]>
Reviewed-by: Andrew Lunn <[e-mail]>
Signed-off-by: Marc Kleine-Budde <[e-mail]>

drivers/net/can/c_can/Makefile

···
 #
 
 obj-$(CONFIG_CAN_C_CAN) += c_can.o
+
+c_can-objs :=
+c_can-objs += c_can_ethtool.o
+c_can-objs += c_can_main.o
+
 obj-$(CONFIG_CAN_C_CAN_PLATFORM) += c_can_platform.o
 obj-$(CONFIG_CAN_C_CAN_PCI) += c_can_pci.o

drivers/net/can/c_can/c_can.c drivers/net/can/c_can/c_can_main.c

···
 
 	dev->flags |= IFF_ECHO;	/* we support local echo */
 	dev->netdev_ops = &c_can_netdev_ops;
+	c_can_set_ethtool_ops(dev);
 
 	err = register_candev(dev);
 	if (!err)

drivers/net/can/c_can/c_can.h

···
 int c_can_power_down(struct net_device *dev);
 #endif
 
+void c_can_set_ethtool_ops(struct net_device *dev);
+
 #endif /* C_CAN_H */

drivers/net/can/c_can/c_can_ethtool.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2021, Dario Binacchi <[e-mail]>
+ */
+
+#include <linux/ethtool.h>
+#include <linux/kernel.h>
+#include <linux/platform_device.h>
+#include <linux/netdevice.h>
+#include <linux/can/dev.h>
+
+#include "c_can.h"
+
+static void c_can_get_drvinfo(struct net_device *netdev,
+			      struct ethtool_drvinfo *info)
+{
+	struct c_can_priv *priv = netdev_priv(netdev);
+	struct platform_device *pdev = to_platform_device(priv->device);
+
+	strscpy(info->driver, "c_can", sizeof(info->driver));
+	strscpy(info->bus_info, pdev->name, sizeof(info->bus_info));
+}
+
+static void c_can_get_ringparam(struct net_device *netdev,
+				struct ethtool_ringparam *ring)
+{
+	struct c_can_priv *priv = netdev_priv(netdev);
+
+	ring->rx_max_pending = priv->msg_obj_num;
+	ring->tx_max_pending = priv->msg_obj_num;
+	ring->rx_pending = priv->msg_obj_rx_num;
+	ring->tx_pending = priv->msg_obj_tx_num;
+}
+
+static const struct ethtool_ops c_can_ethtool_ops = {
+	.get_drvinfo = c_can_get_drvinfo,
+	.get_ringparam = c_can_get_ringparam,
+};
+
+void c_can_set_ethtool_ops(struct net_device *netdev)
+{
+	netdev->ethtool_ops = &c_can_ethtool_ops;
+}