bus: ixp4xx: Add a driver for IXP4xx expansion bus

The Intel IXP4xx SoCs have an expansion bus that is usually just
used for flash memory and configured by the boot loaders and can
be accessed using the "simple-bus".

However some devices need more elaborate configuration and then we
need to provide a proper 3-unit address space indicating chip
select for each device and provide timing and similar information.

Cc: Marc Zyngier <maz@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

MAINTAINERS

@@ -2009,10 +2009,12 @@ M:	Krzysztof Halasa <khalasa@piap.pl>
 L:	linux-arm-kernel@lists.infradead.org (moderated for non-subscribers)
 S:	Maintained
 F:	Documentation/devicetree/bindings/arm/intel-ixp4xx.yaml
+F:	Documentation/devicetree/bindings/bus/intel,ixp4xx-expansion-bus-controller.yaml
 F:	Documentation/devicetree/bindings/gpio/intel,ixp4xx-gpio.txt
 F:	Documentation/devicetree/bindings/interrupt-controller/intel,ixp4xx-interrupt.yaml
 F:	Documentation/devicetree/bindings/timer/intel,ixp4xx-timer.yaml
 F:	arch/arm/mach-ixp4xx/
+F:	drivers/bus/intel-ixp4xx-eb.c
 F:	drivers/clocksource/timer-ixp4xx.c
 F:	drivers/crypto/ixp4xx_crypto.c
 F:	drivers/gpio/gpio-ixp4xx.c

drivers/bus/Kconfig

@@ -95,6 +95,17 @@ config IMX_WEIM
 	  The WEIM(Wireless External Interface Module) works like a bus.
 	  You can attach many different devices on it, such as NOR, onenand.
 
+config INTEL_IXP4XX_EB
+	bool "Intel IXP4xx expansion bus interface driver"
+	depends on HAS_IOMEM
+	depends on ARCH_IXP4XX || COMPILE_TEST
+	default ARCH_IXP4XX
+	select MFD_SYSCON
+	help
+	  Driver for the Intel IXP4xx expansion bus interface. The driver is
+	  needed to set up various chip select configuration parameters before
+	  devices on the expansion bus can be discovered.
+
 config MIPS_CDMM
 	bool "MIPS Common Device Memory Map (CDMM) Driver"
 	depends on CPU_MIPSR2 || CPU_MIPSR5

drivers/bus/Makefile

@@ -16,6 +16,7 @@ obj-$(CONFIG_FSL_MC_BUS)	+= fsl-mc/
 obj-$(CONFIG_BT1_APB)		+= bt1-apb.o
 obj-$(CONFIG_BT1_AXI)		+= bt1-axi.o
 obj-$(CONFIG_IMX_WEIM)		+= imx-weim.o
+obj-$(CONFIG_INTEL_IXP4XX_EB)	+= intel-ixp4xx-eb.o
 obj-$(CONFIG_MIPS_CDMM)		+= mips_cdmm.o
 obj-$(CONFIG_MVEBU_MBUS) 	+= mvebu-mbus.o