HID: wiimote: lock DRM mode during debugfs overwrite

If we write a DRM mode via debugfs, we shouldn't allow normal operations
to overwrite this DRM mode. This is important if we want to debug
3rd-party devices and we want to see what data is sent on each mode.

If we write NULL/0 as DRM, the lock is removed again so the best matching
DRM is chosen by wiimote core.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
diff --git a/drivers/hid/hid-wiimote-debug.c b/drivers/hid/hid-wiimote-debug.c
index 0c0deaa..6e76a2c 100644
--- a/drivers/hid/hid-wiimote-debug.c
+++ b/drivers/hid/hid-wiimote-debug.c
@@ -154,7 +154,10 @@
 		i = simple_strtoul(buf, NULL, 10);
 
 	spin_lock_irqsave(&dbg->wdata->state.lock, flags);
+	dbg->wdata->state.flags &= ~WIIPROTO_FLAG_DRM_LOCKED;
 	wiiproto_req_drm(dbg->wdata, (__u8) i);
+	if (i != WIIPROTO_REQ_NULL)
+		dbg->wdata->state.flags |= WIIPROTO_FLAG_DRM_LOCKED;
 	spin_unlock_irqrestore(&dbg->wdata->state.lock, flags);
 
 	return len;