net: dsa: modularize DSA_TAG_PROTO_NONE

There is no reason that I can see why the no-op tagging protocol should
be registered manually, so make it a module and make all drivers which
have any sort of reference to DSA_TAG_PROTO_NONE select it.

Note that I don't know if ksz_get_tag_protocol() really needs this,
or if it's just the logic which is poorly written. All switches seem to
have their own tagging protocol, and DSA_TAG_PROTO_NONE is just a
fallback that never gets used.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/dsa/Kconfig

@@ -18,6 +18,7 @@ config NET_DSA_BCM_SF2
 
 config NET_DSA_LOOP
 	tristate "DSA mock-up Ethernet switch chip support"
+	select NET_DSA_TAG_NONE
 	select FIXED_PHY
 	help
 	  This enables support for a fake mock-up switch chip which
@@ -99,6 +100,7 @@ config NET_DSA_SMSC_LAN9303_MDIO
 
 config NET_DSA_VITESSE_VSC73XX
 	tristate
+	select NET_DSA_TAG_NONE
 	select FIXED_PHY
 	select VITESSE_PHY
 	select GPIOLIB

drivers/net/dsa/b53/Kconfig

@@ -2,6 +2,7 @@
 menuconfig B53
 	tristate "Broadcom BCM53xx managed switch support"
 	depends on NET_DSA
+	select NET_DSA_TAG_NONE
 	select NET_DSA_TAG_BRCM
 	select NET_DSA_TAG_BRCM_LEGACY
 	select NET_DSA_TAG_BRCM_PREPEND

drivers/net/dsa/microchip/Kconfig

@@ -3,6 +3,7 @@ menuconfig NET_DSA_MICROCHIP_KSZ_COMMON
 	tristate "Microchip KSZ8795/KSZ9477/LAN937x series switch support"
 	depends on NET_DSA
 	select NET_DSA_TAG_KSZ
+	select NET_DSA_TAG_NONE
 	help
 	  This driver adds support for Microchip KSZ9477 series switch and
 	  KSZ8795/KSZ88x3 switch chips.

net/dsa/Kconfig

@@ -18,6 +18,12 @@ if NET_DSA
 
 # Drivers must select the appropriate tagging format(s)
 
+config NET_DSA_TAG_NONE
+	tristate "No-op tag driver"
+	help
+	  Say Y or M if you want to enable support for switches which don't tag
+	  frames over the CPU port.
+
 config NET_DSA_TAG_AR9331
 	tristate "Tag driver for Atheros AR9331 SoC with built-in switch"
 	help

net/dsa/Makefile

@@ -20,6 +20,7 @@ obj-$(CONFIG_NET_DSA_TAG_HELLCREEK) += tag_hellcreek.o
 obj-$(CONFIG_NET_DSA_TAG_KSZ) += tag_ksz.o
 obj-$(CONFIG_NET_DSA_TAG_LAN9303) += tag_lan9303.o
 obj-$(CONFIG_NET_DSA_TAG_MTK) += tag_mtk.o
+obj-$(CONFIG_NET_DSA_TAG_NONE) += tag_none.o
 obj-$(CONFIG_NET_DSA_TAG_OCELOT) += tag_ocelot.o
 obj-$(CONFIG_NET_DSA_TAG_OCELOT_8021Q) += tag_ocelot_8021q.o
 obj-$(CONFIG_NET_DSA_TAG_QCA) += tag_qca.o

net/dsa/dsa.c

@@ -18,22 +18,6 @@
 static LIST_HEAD(dsa_tag_drivers_list);
 static DEFINE_MUTEX(dsa_tag_drivers_lock);
 
-static struct sk_buff *dsa_slave_notag_xmit(struct sk_buff *skb,
-					    struct net_device *dev)
-{
-	/* Just return the original SKB */
-	return skb;
-}
-
-static const struct dsa_device_ops none_ops = {
-	.name	= "none",
-	.proto	= DSA_TAG_PROTO_NONE,
-	.xmit	= dsa_slave_notag_xmit,
-	.rcv	= NULL,
-};
-
-DSA_TAG_DRIVER(none_ops);
-
 static void dsa_tag_driver_register(struct dsa_tag_driver *dsa_tag_driver,
 				    struct module *owner)
 {
@@ -551,9 +535,6 @@ static int __init dsa_init_module(void)
 
 	dev_add_pack(&dsa_pack_type);
 
-	dsa_tag_driver_register(&DSA_TAG_DRIVER_NAME(none_ops),
-				THIS_MODULE);
-
 	rc = rtnl_link_register(&dsa_link_ops);
 	if (rc)
 		goto netlink_register_fail;
@@ -561,7 +542,6 @@ static int __init dsa_init_module(void)
 	return 0;
 
 netlink_register_fail:
-	dsa_tag_driver_unregister(&DSA_TAG_DRIVER_NAME(none_ops));
 	dsa_slave_unregister_notifier();
 	dev_remove_pack(&dsa_pack_type);
 register_notifier_fail:
@@ -574,7 +554,6 @@ module_init(dsa_init_module);
 static void __exit dsa_cleanup_module(void)
 {
 	rtnl_link_unregister(&dsa_link_ops);
-	dsa_tag_driver_unregister(&DSA_TAG_DRIVER_NAME(none_ops));
 
 	dsa_slave_unregister_notifier();
 	dev_remove_pack(&dsa_pack_type);

net/dsa/dsa_priv.h

@@ -384,7 +384,6 @@ int dsa_port_change_master(struct dsa_port *dp, struct net_device *master,
 			   struct netlink_ext_ack *extack);
 
 /* slave.c */
-extern const struct dsa_device_ops notag_netdev_ops;
 extern struct notifier_block dsa_slave_switchdev_notifier;
 extern struct notifier_block dsa_slave_switchdev_blocking_notifier;
 

net/dsa/tag_none.c

@@ -0,0 +1,30 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * net/dsa/tag_none.c - Traffic handling for switches with no tag
+ * Copyright (c) 2008-2009 Marvell Semiconductor
+ * Copyright (c) 2013 Florian Fainelli <florian@openwrt.org>
+ *
+ * WARNING: do not use this for new switches. In case of no hardware
+ * tagging support, look at tag_8021q.c instead.
+ */
+
+#include "dsa_priv.h"
+
+#define NONE_NAME	"none"
+
+static struct sk_buff *dsa_slave_notag_xmit(struct sk_buff *skb,
+					    struct net_device *dev)
+{
+	/* Just return the original SKB */
+	return skb;
+}
+
+static const struct dsa_device_ops none_ops = {
+	.name	= NONE_NAME,
+	.proto	= DSA_TAG_PROTO_NONE,
+	.xmit	= dsa_slave_notag_xmit,
+};
+
+module_dsa_tag_driver(none_ops);
+MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_NONE, NONE_NAME);
+MODULE_LICENSE("GPL");