dsa: simplify Kconfig symbols and dependencies

1. Remove CONFIG_HAVE_NET_DSA.

CONFIG_HAVE_NET_DSA is a legacy leftover from the times when drivers
should have selected CONFIG_NET_DSA manually.
Currently, all drivers has explicit 'depends on NET_DSA', so this is
no more needed.

2. CONFIG_HAVE_NET_DSA dependencies became CONFIG_NET_DSA's ones.

 - dropped !S390 dependency which was introduced to be sure NET_DSA
   can select CONFIG_PHYLIB. DSA migrated to Phylink almost 3 years
   ago and the PHY library itself doesn't depend on !S390 since
   commit 870a2b5e ("phylib: remove !S390 dependeny from Kconfig");
 - INET dependency is kept to be sure we can select NET_SWITCHDEV;
 - NETDEVICES dependency is kept to be sure we can select PHYLINK.

3. DSA drivers menu now depends on NET_DSA.

Instead on 'depends on NET_DSA' on every single driver, the entire
menu now depends on it. This eliminates a lot of duplicated lines
from Kconfig with no loss (when CONFIG_NET_DSA=m, drivers also can
be only m or n).
This also has a nice side effect that there's no more empty menu on
configurations without DSA.

4. Kbuild will now descend into 'drivers/net/dsa' only when
   CONFIG_NET_DSA is y or m.

This is safe since no objects inside this folder can be built without
DSA core, as well as when CONFIG_NET_DSA=m, no objects can be
built-in.
Signed-off-by: Alexander Lobakin <alobakin@pm.me>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/Makefile

@@ -45,7 +45,7 @@ obj-$(CONFIG_ARCNET) += arcnet/
 obj-$(CONFIG_DEV_APPLETALK) += appletalk/
 obj-$(CONFIG_CAIF) += caif/
 obj-$(CONFIG_CAN) += can/
-obj-y += dsa/
+obj-$(CONFIG_NET_DSA) += dsa/
 obj-$(CONFIG_ETHERNET) += ethernet/
 obj-$(CONFIG_FDDI) += fddi/
 obj-$(CONFIG_HIPPI) += hippi/

drivers/net/dsa/Kconfig

 # SPDX-License-Identifier: GPL-2.0-only
 menu "Distributed Switch Architecture drivers"
-	depends on HAVE_NET_DSA
+	depends on NET_DSA
 
 source "drivers/net/dsa/b53/Kconfig"
 
 config NET_DSA_BCM_SF2
 	tristate "Broadcom Starfighter 2 Ethernet switch support"
-	depends on HAS_IOMEM && NET_DSA
+	depends on HAS_IOMEM
 	select NET_DSA_TAG_BRCM
 	select FIXED_PHY
 	select BCM7XXX_PHY
@@ -18,7 +18,6 @@ config NET_DSA_BCM_SF2
 
 config NET_DSA_LOOP
 	tristate "DSA mock-up Ethernet switch chip support"
-	depends on NET_DSA
 	select FIXED_PHY
 	help
 	  This enables support for a fake mock-up switch chip which
@@ -28,7 +27,7 @@ source "drivers/net/dsa/hirschmann/Kconfig"
 
 config NET_DSA_LANTIQ_GSWIP
 	tristate "Lantiq / Intel GSWIP"
-	depends on HAS_IOMEM && NET_DSA
+	depends on HAS_IOMEM
 	select NET_DSA_TAG_GSWIP
 	help
 	  This enables support for the Lantiq / Intel GSWIP 2.1 found in
@@ -36,7 +35,6 @@ config NET_DSA_LANTIQ_GSWIP
 
 config NET_DSA_MT7530
 	tristate "MediaTek MT753x and MT7621 Ethernet switch support"
-	depends on NET_DSA
 	select NET_DSA_TAG_MTK
 	help
 	  This enables support for the MediaTek MT7530, MT7531, and MT7621
@@ -44,7 +42,6 @@ config NET_DSA_MT7530
 
 config NET_DSA_MV88E6060
 	tristate "Marvell 88E6060 ethernet switch chip support"
-	depends on NET_DSA
 	select NET_DSA_TAG_TRAILER
 	help
 	  This enables support for the Marvell 88E6060 ethernet switch
@@ -64,7 +61,6 @@ source "drivers/net/dsa/xrs700x/Kconfig"
 
 config NET_DSA_QCA8K
 	tristate "Qualcomm Atheros QCA8K Ethernet switch family support"
-	depends on NET_DSA
 	select NET_DSA_TAG_QCA
 	select REGMAP
 	help
@@ -73,7 +69,6 @@ config NET_DSA_QCA8K
 
 config NET_DSA_REALTEK_SMI
 	tristate "Realtek SMI Ethernet switch family support"
-	depends on NET_DSA
 	select NET_DSA_TAG_RTL4_A
 	select FIXED_PHY
 	select IRQ_DOMAIN
@@ -93,7 +88,7 @@ config NET_DSA_SMSC_LAN9303
 
 config NET_DSA_SMSC_LAN9303_I2C
 	tristate "SMSC/Microchip LAN9303 3-ports 10/100 ethernet switch in I2C managed mode"
-	depends on NET_DSA && I2C
+	depends on I2C
 	select NET_DSA_SMSC_LAN9303
 	select REGMAP_I2C
 	help
@@ -102,7 +97,6 @@ config NET_DSA_SMSC_LAN9303_I2C
 
 config NET_DSA_SMSC_LAN9303_MDIO
 	tristate "SMSC/Microchip LAN9303 3-ports 10/100 ethernet switch in MDIO managed mode"
-	depends on NET_DSA
 	select NET_DSA_SMSC_LAN9303
 	help
 	  Enable access functions if the SMSC/Microchip LAN9303 is configured
@@ -110,7 +104,6 @@ config NET_DSA_SMSC_LAN9303_MDIO
 
 config NET_DSA_VITESSE_VSC73XX
 	tristate
-	depends on NET_DSA
 	select FIXED_PHY
 	select VITESSE_PHY
 	select GPIOLIB
@@ -120,7 +113,6 @@ config NET_DSA_VITESSE_VSC73XX
 
 config NET_DSA_VITESSE_VSC73XX_SPI
 	tristate "Vitesse VSC7385/7388/7395/7398 SPI mode support"
-	depends on NET_DSA
 	depends on SPI
 	select NET_DSA_VITESSE_VSC73XX
 	help
@@ -129,7 +121,6 @@ config NET_DSA_VITESSE_VSC73XX_SPI
 
 config NET_DSA_VITESSE_VSC73XX_PLATFORM
 	tristate "Vitesse VSC7385/7388/7395/7398 Platform mode support"
-	depends on NET_DSA
 	depends on HAS_IOMEM
 	select NET_DSA_VITESSE_VSC73XX
 	help

net/dsa/Kconfig

 # SPDX-License-Identifier: GPL-2.0-only
-config HAVE_NET_DSA
-	def_bool y
-	depends on INET && NETDEVICES && !S390
-
-# Drivers must select NET_DSA and the appropriate tagging format
 
 menuconfig NET_DSA
 	tristate "Distributed Switch Architecture"
-	depends on HAVE_NET_DSA
 	depends on BRIDGE || BRIDGE=n
 	depends on HSR || HSR=n
+	depends on INET && NETDEVICES
 	select GRO_CELLS
 	select NET_SWITCHDEV
 	select PHYLINK
@@ -20,7 +15,8 @@ menuconfig NET_DSA
 
 if NET_DSA
 
-# tagging formats
+# Drivers must select the appropriate tagging format(s)
+
 config NET_DSA_TAG_8021Q
 	tristate
 	select VLAN_8021Q