irqchip: Add IMX MU MSI controller driver

The MU block found in a number of Freescale/NXP SoCs supports generating
IRQs by writing data to a register.

This enables the MU block to be used as a MSI controller, by leveraging
the platform-MSI API.
Signed-off-by: Frank Li <Frank.Li@nxp.com>
[maz: dropped pointless dma-iommu.h and of_pci.h includes]
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220922161246.20586-4-Frank.Li@nxp.com

drivers/irqchip/Kconfig

@@ -481,6 +481,20 @@ config IMX_INTMUX
 	help
 	  Support for the i.MX INTMUX interrupt multiplexer.
 
+config IMX_MU_MSI
+	tristate "i.MX MU used as MSI controller"
+	depends on OF && HAS_IOMEM
+	default m if ARCH_MXC
+	select IRQ_DOMAIN
+	select IRQ_DOMAIN_HIERARCHY
+	select GENERIC_MSI_IRQ_DOMAIN
+	help
+	  Provide a driver for the MU block used as a CPU-to-CPU MSI
+	  controller. This requires a specially crafted DT to make use
+	  of this driver.
+
+	  If unsure, say N
+
 config LS1X_IRQ
 	bool "Loongson-1 Interrupt Controller"
 	depends on MACH_LOONGSON32

drivers/irqchip/Makefile

@@ -99,6 +99,7 @@ obj-$(CONFIG_RISCV_INTC)		+= irq-riscv-intc.o
 obj-$(CONFIG_SIFIVE_PLIC)		+= irq-sifive-plic.o
 obj-$(CONFIG_IMX_IRQSTEER)		+= irq-imx-irqsteer.o
 obj-$(CONFIG_IMX_INTMUX)		+= irq-imx-intmux.o
+obj-$(CONFIG_IMX_MU_MSI)		+= irq-imx-mu-msi.o
 obj-$(CONFIG_MADERA_IRQ)		+= irq-madera.o
 obj-$(CONFIG_LS1X_IRQ)			+= irq-ls1x.o
 obj-$(CONFIG_TI_SCI_INTR_IRQCHIP)	+= irq-ti-sci-intr.o