Provide a variant of DEFINE_RES that takes 0 arguments to initialize an
"unset" resource descriptor.

This should be used for the improper case of

	struct resource res = {};

where DEFINE_RES() should be used.

With this new helper variant, it would result in:

	struct resource res = DEFINE_RES();

instead of having to define the full 3 arguments:

	struct resource res = DEFINE_RES(0, 0, IORESOURCE_UNSET);

DEFINE_RES() with no args, will set the flags to IORESOURCE_UNSET
signaling the resource descriptor is UNSET and doesn't reflect an actual
resource currently.

Suggested-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Reviewed-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
---
Changes v2:
- Add missing header
- Make one line
- Add review tag

 include/linux/ioport.h | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/linux/ioport.h b/include/linux/ioport.h
index d3e837eb8760..5779187f8698 100644
--- a/include/linux/ioport.h
+++ b/include/linux/ioport.h
@@ -10,6 +10,7 @@
 #define _LINUX_IOPORT_H
 
 #ifndef __ASSEMBLY__
+#include <linux/args.h>
 #include <linux/bits.h>
 #include <linux/compiler.h>
 #include <linux/minmax.h>
@@ -168,8 +169,12 @@ enum {
 
 #define DEFINE_RES_NAMED(_start, _size, _name, _flags)			\
 	DEFINE_RES_NAMED_DESC(_start, _size, _name, _flags, IORES_DESC_NONE)
-#define DEFINE_RES(_start, _size, _flags)				\
+#define __DEFINE_RES0()							\
+	DEFINE_RES_NAMED(0, 0, NULL, IORESOURCE_UNSET)
+#define __DEFINE_RES3(_start, _size, _flags)				\
 	DEFINE_RES_NAMED(_start, _size, NULL, _flags)
+#define DEFINE_RES(...)							\
+	CONCATENATE(__DEFINE_RES, COUNT_ARGS(__VA_ARGS__))(__VA_ARGS__)
 
 #define DEFINE_RES_IO_NAMED(_start, _size, _name)			\
 	DEFINE_RES_NAMED((_start), (_size), (_name), IORESOURCE_IO)
-- 
2.51.0