s390/diag: add a statistic for diagnose calls

Introduce /sys/debug/kernel/diag_stat with a statistic how many diagnose
calls have been done by each CPU in the system.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/drivers/s390/char/diag_ftp.c b/drivers/s390/char/diag_ftp.c
index 12db8db..a5ccbf6 100644
--- a/drivers/s390/char/diag_ftp.c
+++ b/drivers/s390/char/diag_ftp.c
@@ -15,6 +15,7 @@
 #include <linux/wait.h>
 #include <linux/string.h>
 #include <asm/ctl_reg.h>
+#include <asm/diag.h>
 
 #include "hmcdrv_ftp.h"
 #include "diag_ftp.h"
@@ -102,6 +103,7 @@
 {
 	int rc;
 
+	diag_stat_inc(DIAG_STAT_X2C4);
 	asm volatile(
 		"	diag	%[addr],%[cmd],0x2c4\n"
 		"0:	j	2f\n"