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>

drivers/hid/hid-wiimote-core.c

@@ -242,7 +242,9 @@ void wiiproto_req_drm(struct wiimote_data *wdata, __u8 drm)
 {
 	__u8 cmd[3];
 
-	if (drm == WIIPROTO_REQ_NULL)
+	if (wdata->state.flags & WIIPROTO_FLAG_DRM_LOCKED)
+		drm = wdata->state.drm;
+	else if (drm == WIIPROTO_REQ_NULL)
 		drm = select_drm(wdata);
 
 	cmd[0] = WIIPROTO_REQ_DRM;

drivers/hid/hid-wiimote-debug.c

@@ -154,7 +154,10 @@ static ssize_t wiidebug_drm_write(struct file *f, const char __user *u,
 		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;

drivers/hid/hid-wiimote.h

@@ -43,6 +43,7 @@
 #define WIIPROTO_FLAG_MP_USED		0x1000
 #define WIIPROTO_FLAG_MP_ACTIVE		0x2000
 #define WIIPROTO_FLAG_EXITING		0x4000
+#define WIIPROTO_FLAG_DRM_LOCKED	0x8000
 
 #define WIIPROTO_FLAGS_LEDS (WIIPROTO_FLAG_LED1 | WIIPROTO_FLAG_LED2 | \
 					WIIPROTO_FLAG_LED3 | WIIPROTO_FLAG_LED4)