irqchip/dw-apb-ictl: Support building as module

The driver is now always built in. In some synaptics ARM64 SoCs it is used
as a second level interrupt controller hanging off the ARM GIC and is
therefore loadable during boot.

Enable it to be built as a module and handle built-in usage correctly, so
that it continues working on systems where it is the main interrupt
controller.

[ tglx: Massage changelog ]

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240614153449.2083-1-jszhang@kernel.org

drivers/irqchip/Kconfig

@@ -145,7 +145,7 @@ config DAVINCI_CP_INTC
 	select IRQ_DOMAIN
 
 config DW_APB_ICTL
-	bool
+	tristate "DesignWare APB Interrupt Controller"
 	select GENERIC_IRQ_CHIP
 	select IRQ_DOMAIN_HIERARCHY
 

drivers/irqchip/irq-dw-apb-ictl.c

@@ -122,7 +122,7 @@ static int __init dw_apb_ictl_init(struct device_node *np,
 	int ret, nrirqs, parent_irq, i;
 	u32 reg;
 
-	if (!parent) {
+	if (!parent && IS_BUILTIN(CONFIG_DW_APB_ICTL)) {
 		/* Used as the primary interrupt controller */
 		parent_irq = 0;
 		domain_ops = &dw_apb_ictl_irq_domain_ops;
@@ -214,5 +214,12 @@ static int __init dw_apb_ictl_init(struct device_node *np,
 	release_mem_region(r.start, resource_size(&r));
 	return ret;
 }
-IRQCHIP_DECLARE(dw_apb_ictl,
-		"snps,dw-apb-ictl", dw_apb_ictl_init);
+#if IS_BUILTIN(CONFIG_DW_APB_ICTL)
+IRQCHIP_DECLARE(dw_apb_ictl, "snps,dw-apb-ictl", dw_apb_ictl_init);
+#else
+IRQCHIP_PLATFORM_DRIVER_BEGIN(dw_apb_ictl)
+IRQCHIP_MATCH("snps,dw-apb-ictl", dw_apb_ictl_init)
+IRQCHIP_PLATFORM_DRIVER_END(dw_apb_ictl)
+MODULE_DESCRIPTION("DesignWare APB Interrupt Controller");
+MODULE_LICENSE("GPL v2");
+#endif