s390/cio: introduce pathmask_to_pos

We often need to correlate an 8 bit path mask with the position
in a channel path array. Introduce and use pathmask_to_pos for
that task.

Reviewed-by: Peter Oberparleiter <oberpar@linux.vnet.ibm.com>
Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/cio.h

@@ -5,6 +5,7 @@
 #define _ASM_S390_CIO_H_
 
 #include <linux/spinlock.h>
+#include <linux/bitops.h>
 #include <asm/types.h>
 
 #define LPM_ANYPATH 0xff
@@ -296,6 +297,15 @@ static inline int ccw_dev_id_is_equal(struct ccw_dev_id *dev_id1,
 	return 0;
 }
 
+/**
+ * pathmask_to_pos() - find the position of the left-most bit in a pathmask
+ * @mask: pathmask with at least one bit set
+ */
+static inline u8 pathmask_to_pos(u8 mask)
+{
+	return 8 - ffs(mask);
+}
+
 void channel_subsystem_reinit(void);
 extern void css_schedule_reprobe(void);