s390/cio: introduce CIO debugfs directory

This patch introduces an s390 Common I/O layer debugfs directory that is
intended to provide access to debugging-related CIO functions and data.
The directory is created as /sys/kernel/debug/s390/cio

Signed-off-by: Vineeth Vijayan <[e-mail]>
Reviewed-by: Peter Oberparleiter <[e-mail]>
Signed-off-by: Heiko Carstens <[e-mail]>

drivers/s390/cio/Makefile

···
 CFLAGS_vfio_ccw_trace.o := -I$(src)
 
 obj-y += airq.o blacklist.o chsc.o cio.o css.o chp.o idset.o isc.o \
-	fcx.o itcw.o crw.o ccwreq.o trace.o ioasm.o
+	fcx.o itcw.o crw.o ccwreq.o trace.o ioasm.o cio_debugfs.o
 ccw_device-objs += device.o device_fsm.o device_ops.o
 ccw_device-objs += device_id.o device_pgid.o device_status.o
 obj-y += ccw_device.o cmf.o

drivers/s390/cio/cio_debug.h

···
 	debug_event(cio_debug_trace_id, level, data, length);
 }
 
+/* For the CIO debugfs related features */
+extern struct dentry *cio_debugfs_dir;
+
 #endif

drivers/s390/cio/cio_debugfs.c

···
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *   S/390 common I/O debugfs interface
+ *
+ *    Copyright IBM Corp. 2021
+ *    Author(s): Vineeth Vijayan <[e-mail]>
+ */
+
+#include <linux/debugfs.h>
+#include "cio_debug.h"
+
+struct dentry *cio_debugfs_dir;
+
+/* Create the debugfs directory for CIO under the arch_debugfs_dir
+ * i.e /sys/kernel/debug/s390/cio
+ */
+static int __init cio_debugfs_init(void)
+{
+	cio_debugfs_dir = debugfs_create_dir("cio", arch_debugfs_dir);
+
+	return 0;
+}
+subsys_initcall(cio_debugfs_init);