bus: uniphier-system-bus: add UniPhier System Bus driver

Since commit 1517126fda ("ARM: uniphier: select DM_ETH"), DM-based
drivers/net/smc911x.c is compiled, but it is never probed because the
parent node lacks the DM-based driver.

I need a skeleton driver to populate child devices (but the next commit
will move more hardware settings to the this driver).

I put this to drivers/bus/uniphier-system-bus.c because this is the
same path as the driver in Linux kernel.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

arch/arm/mach-uniphier/Kconfig

@@ -83,6 +83,7 @@ config CACHE_UNIPHIER
 
 config MICRO_SUPPORT_CARD
 	bool "Use Micro Support Card"
+	depends on UNIPHIER_SYSTEM_BUS
 	help
 	  This option provides support for the expansion board, available
 	  on some UniPhier reference boards.

drivers/Kconfig

@@ -10,6 +10,8 @@ source "drivers/ata/Kconfig"
 
 source "drivers/axi/Kconfig"
 
+source "drivers/bus/Kconfig"
+
 source "drivers/block/Kconfig"
 
 source "drivers/bootcount/Kconfig"

drivers/Makefile

@@ -74,6 +74,7 @@ ifeq ($(CONFIG_SPL_BUILD)$(CONFIG_TPL_BUILD),)
 
 obj-y += adc/
 obj-y += ata/
+obj-y += bus/
 obj-$(CONFIG_DM_DEMO) += demo/
 obj-$(CONFIG_BIOSEMU) += bios_emulator/
 obj-y += block/

drivers/bus/Kconfig

@@ -0,0 +1,16 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Bus Devices
+#
+
+menu "Bus devices"
+
+config UNIPHIER_SYSTEM_BUS
+	bool "UniPhier System Bus driver"
+	depends on ARCH_UNIPHIER
+	default y
+	help
+	  Support for UniPhier System Bus, a simple external bus.  This is
+	  needed to use on-board devices connected to UniPhier SoCs.
+
+endmenu

drivers/bus/Makefile

@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Makefile for the bus drivers.
+#
+
+obj-$(CONFIG_UNIPHIER_SYSTEM_BUS) += uniphier-system-bus.o

drivers/bus/uniphier-system-bus.c

@@ -0,0 +1,14 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <dm.h>
+
+static const struct udevice_id uniphier_system_bus_match[] = {
+	{ .compatible = "socionext,uniphier-system-bus" },
+	{ /* sentinel */ }
+};
+
+U_BOOT_DRIVER(uniphier_system_bus_driver) = {
+	.name	= "uniphier-system-bus",
+	.id	= UCLASS_SIMPLE_BUS,
+	.of_match = uniphier_system_bus_match,
+};