irqchip/xilinx: Add support for parent intc

The MIPS based xilfpga platform has the following IRQ structure

Peripherals --> xilinx_intcontroller -> mips_cpu_int controller

Add support for the driver to chain the irq handler
Signed-off-by: Zubair Lutfullah Kakakhel <Zubair.Kakakhel@imgtec.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

drivers/irqchip/irq-xilinx-intc.c

@@ -12,10 +12,12 @@
 #include <linux/irqdomain.h>
 #include <linux/irq.h>
 #include <linux/irqchip.h>
+#include <linux/irqchip/chained_irq.h>
 #include <linux/of_address.h>
 #include <linux/io.h>
 #include <linux/jump_label.h>
 #include <linux/bug.h>
+#include <linux/of_irq.h>
 
 /* No one else should require these constants, so define them locally here. */
 #define ISR 0x00			/* Interrupt Status Register */
@@ -133,11 +135,26 @@ static const struct irq_domain_ops xintc_irq_domain_ops = {
 	.map = xintc_map,
 };
 
+static void xil_intc_irq_handler(struct irq_desc *desc)
+{
+	struct irq_chip *chip = irq_desc_get_chip(desc);
+	u32 pending;
+
+	chained_irq_enter(chip, desc);
+	do {
+		pending = xintc_get_irq();
+		if (pending == -1U)
+			break;
+		generic_handle_irq(pending);
+	} while (true);
+	chained_irq_exit(chip, desc);
+}
+
 static int __init xilinx_intc_of_init(struct device_node *intc,
 					     struct device_node *parent)
 {
 	u32 nr_irq;
-	int ret;
+	int ret, irq;
 	struct xintc_irq_chip *irqc;
 
 	if (xintc_irqc) {
@@ -196,7 +213,20 @@ static int __init xilinx_intc_of_init(struct device_node *intc,
 		goto err_alloc;
 	}
 
-	irq_set_default_host(irqc->root_domain);
+	if (parent) {
+		irq = irq_of_parse_and_map(intc, 0);
+		if (irq) {
+			irq_set_chained_handler_and_data(irq,
+							 xil_intc_irq_handler,
+							 irqc);
+		} else {
+			pr_err("irq-xilinx: interrupts property not in DT\n");
+			ret = -EINVAL;
+			goto err_alloc;
+		}
+	} else {
+		irq_set_default_host(irqc->root_domain);
+	}
 
 	return 0;