rpi4: Add GIC maintenance interrupt to GIC DT node

For being able to use the virtualisation support the GIC offers, we need
to know the interrupt number of the maintenance interrupt. This
information is missing from the official RPi4 device tree.

Use libfdt to add the "interrupts" property to the GIC node, which
allows hypervisors like KVM or Xen to be able to use the GIC's help on
virtualising interrupts.

Change-Id: Iab84f0885a5bf29fb84ca8f385e8a39d27700c75
Signed-off-by: Andre Przywara <andre.przywara@arm.com>

plat/rpi/rpi4/rpi4_bl31_setup.c

@@ -222,7 +222,8 @@ static uint32_t dtb_size(const void *dtb)
 static void rpi4_prepare_dtb(void)
 {
 	void *dtb = (void *)rpi4_get_dtb_address();
-	int ret;
+	uint32_t gic_int_prop[3];
+	int ret, offs;
 
 	/* Return if no device tree is detected */
 	if (fdt_check_header(dtb) != 0)
@@ -248,6 +249,12 @@ static void rpi4_prepare_dtb(void)
 	if (fdt_add_reserved_memory(dtb, "atf@0", 0, 0x80000))
 		WARN("Failed to add reserved memory nodes to DT.\n");
 
+	offs = fdt_node_offset_by_compatible(dtb, 0, "arm,gic-400");
+	gic_int_prop[0] = cpu_to_fdt32(1);		// PPI
+	gic_int_prop[1] = cpu_to_fdt32(9);		// PPI #9
+	gic_int_prop[2] = cpu_to_fdt32(0x0f04);		// all cores, level high
+	fdt_setprop(dtb, offs, "interrupts", gic_int_prop, 12);
+
 	ret = fdt_pack(dtb);
 	if (ret < 0)
 		ERROR("Failed to pack Device Tree at %p: error %d\n", dtb, ret);