irqdomain: Allow ACPI device nodes to be used as irqdomain identifiers

A number of irqchip implementations are (ab)using the irqdomain allocator
by passing a fwnode that is neither a FWNODE_OF or a FWNODE_IRQCHIP.

This is pretty bad, but it also feels pretty crap to force these drivers to
allocate their own irqchip_fwid when they already have a proper fwnode.

Instead, let's teach the irqdomain allocator about ACPI device nodes, and
add some lovely name generation code... Tested on an arm64 D05 system.
Reported-and-tested-by: John Garry <john.garry@huawei.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Agustin Vega-Frias <agustinv@codeaurora.org>
Cc: Ma Jun <majun258@huawei.com>
Cc: Hanjun Guo <hanjun.guo@linaro.org>
Link: http://lkml.kernel.org/r/20170707083959.10349-1-marc.zyngier@arm.com

kernel/irq/irqdomain.c

 #define pr_fmt(fmt)  "irq: " fmt
 
+#include <linux/acpi.h>
 #include <linux/debugfs.h>
 #include <linux/hardirq.h>
 #include <linux/interrupt.h>
@@ -155,6 +156,21 @@ struct irq_domain *__irq_domain_add(struct fwnode_handle *fwnode, int size,
 			domain->name = fwid->name;
 			break;
 		}
+#ifdef CONFIG_ACPI
+	} else if (is_acpi_device_node(fwnode)) {
+		struct acpi_buffer buf = {
+			.length = ACPI_ALLOCATE_BUFFER,
+		};
+		acpi_handle handle;
+
+		handle = acpi_device_handle(to_acpi_device_node(fwnode));
+		if (acpi_get_name(handle, ACPI_FULL_PATHNAME, &buf) == AE_OK) {
+			domain->name = buf.pointer;
+			domain->flags |= IRQ_DOMAIN_NAME_ALLOCATED;
+		}
+
+		domain->fwnode = fwnode;
+#endif
 	} else if (of_node) {
 		char *name;