can: Kconfig: turn menu "CAN Device Drivers" into a menuconfig using CAN_DEV

In the next patches, the software/virtual drivers (slcan, v(x)can)
will depend on drivers/net/can/dev/skb.o.

This patch changes the scope of the can-dev module to include the
above mentioned drivers.

To do so, we reuse the menu "CAN Device Drivers" and turn it into a
configmenu using the config symbol CAN_DEV (which we released in
previous patch). Also, add a description to this new CAN_DEV
menuconfig.

The symbol CAN_DEV now only triggers the build of skb.o. For this
reasons, all the macros from linux/module.h are deported from
drivers/net/can/dev/dev.c to drivers/net/can/dev/skb.c.

Finally, drivers/net/can/dev/Makefile is adjusted accordingly.

Link: https://lore.kernel.org/all/20220610143009.323579-3-mailhol.vincent@wanadoo.frSuggested-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Acked-by: Max Staudt <max@enpas.org>
Tested-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/Kconfig

 # SPDX-License-Identifier: GPL-2.0-only
-menu "CAN Device Drivers"
+
+menuconfig CAN_DEV
+	tristate "CAN Device Drivers"
+	default y
+	help
+	  Controller Area Network (CAN) is serial communications protocol up to
+	  1Mbit/s for its original release (now known as Classical CAN) and up
+	  to 8Mbit/s for the more recent CAN with Flexible Data-Rate
+	  (CAN-FD). The CAN bus was originally mainly for automotive, but is now
+	  widely used in marine (NMEA2000), industrial, and medical
+	  applications. More information on the CAN network protocol family
+	  PF_CAN is contained in <Documentation/networking/can.rst>.
+
+	  This section contains all the CAN(-FD) device drivers including the
+	  virtual ones. If you own such devices or plan to use the virtual CAN
+	  interfaces to develop applications, say Y here.
+
+	  To compile as a module, choose M here: the module will be called
+	  can-dev.
+
+if CAN_DEV
 
 config CAN_VCAN
 	tristate "Virtual Local CAN Interface (vcan)"
@@ -49,7 +69,7 @@ config CAN_SLCAN
 	  also be built as a module. If so, the module will be called slcan.
 
 config CAN_NETLINK
-	tristate "CAN device drivers with Netlink support"
+	bool "CAN device drivers with Netlink support"
 	default y
 	help
 	  Enables the common framework for CAN device drivers. This is the
@@ -57,6 +77,9 @@ config CAN_NETLINK
 	  as bittiming validation, support of CAN error states, device restart
 	  and others.
 
+	  The additional features selected by this option will be added to the
+	  can-dev module.
+
 	  This is required by all platform and hardware CAN drivers. If you
 	  plan to use such devices or if unsure, say Y.
 
@@ -178,4 +201,4 @@ config CAN_DEBUG_DEVICES
 	  a problem with CAN support and want to see more of what is going
 	  on.
 
-endmenu
+endif #CAN_DEV

drivers/net/can/dev/Makefile

 # SPDX-License-Identifier: GPL-2.0
 
-obj-$(CONFIG_CAN_NETLINK) += can-dev.o
-can-dev-y			+= bittiming.o
-can-dev-y			+= dev.o
-can-dev-y			+= length.o
-can-dev-y			+= netlink.o
-can-dev-y			+= rx-offload.o
+obj-$(CONFIG_CAN_DEV) += can-dev.o
+
 can-dev-y += skb.o
+
+can-dev-$(CONFIG_CAN_NETLINK) += bittiming.o
+can-dev-$(CONFIG_CAN_NETLINK) += dev.o
+can-dev-$(CONFIG_CAN_NETLINK) += length.o
+can-dev-$(CONFIG_CAN_NETLINK) += netlink.o
+can-dev-$(CONFIG_CAN_NETLINK) += rx-offload.o

drivers/net/can/dev/dev.c

@@ -4,7 +4,6 @@
  * Copyright (C) 2008-2009 Wolfgang Grandegger <wg@grandegger.com>
  */
 
-#include <linux/module.h>
 #include <linux/kernel.h>
 #include <linux/slab.h>
 #include <linux/netdevice.h>
@@ -17,12 +16,6 @@
 #include <linux/gpio/consumer.h>
 #include <linux/of.h>
 
-#define MOD_DESC "CAN device driver interface"
-
-MODULE_DESCRIPTION(MOD_DESC);
-MODULE_LICENSE("GPL v2");
-MODULE_AUTHOR("Wolfgang Grandegger <wg@grandegger.com>");
-
 static void can_update_state_error_stats(struct net_device *dev,
 					 enum can_state new_state)
 {
@@ -513,7 +506,7 @@ static __init int can_dev_init(void)
 
 	err = can_netlink_register();
 	if (!err)
-		pr_info(MOD_DESC "\n");
+		pr_info("CAN device driver interface\n");
 
 	return err;
 }

drivers/net/can/dev/skb.c

@@ -5,6 +5,13 @@
  */
 
 #include <linux/can/dev.h>
+#include <linux/module.h>
+
+#define MOD_DESC "CAN device driver interface"
+
+MODULE_DESCRIPTION(MOD_DESC);
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Wolfgang Grandegger <wg@grandegger.com>");
 
 /* Local echo of CAN messages
  *