[POWERPC] Export virq mapping via debugfs

This adds a debugfs file "powerpc/virq_mapping", which shows the virtual
to real mapping of irq numbers.  Enable it with CONFIG_VIRQ_DEBUG.

Signed-off-by: Zhang Wei <wei.zhang@freescale.com>
Signed-off-by: Chen Gong <G.Chen@freescale.com>
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/arch/powerpc/Kconfig.debug b/arch/powerpc/Kconfig.debug
index 22acece..c38bc22 100644
--- a/arch/powerpc/Kconfig.debug
+++ b/arch/powerpc/Kconfig.debug
@@ -124,6 +124,16 @@
 	  for handling hard and soft interrupts.  This can help avoid
 	  overflowing the process kernel stacks.
 
+config VIRQ_DEBUG
+	bool "Expose hardware/virtual IRQ mapping via debugfs"
+	depends on DEBUG_FS && PPC_MERGE
+	help
+	  This option will show the mapping relationship between hardware irq
+	  numbers and virtual irq numbers. The mapping is exposed via debugfs
+	  in the file powerpc/virq_mapping.
+
+	  If you don't know what this means you don't need it.
+
 config BDI_SWITCH
 	bool "Include BDI-2000 user context switcher"
 	depends on DEBUG_KERNEL && PPC32