vfio/ccw: Refactor vfio_ccw_mdev_reset

Use both the FSM Close and Open events when resetting an mdev,
rather than making a separate call to cio_enable_subchannel().
Signed-off-by: Eric Farman <farman@linux.ibm.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
Link: https://lore.kernel.org/r/20220707135737.720765-11-farman@linux.ibm.comSigned-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/s390/cio/vfio_ccw_ops.c

@@ -21,25 +21,21 @@ static const struct vfio_device_ops vfio_ccw_dev_ops;
 
 static int vfio_ccw_mdev_reset(struct vfio_ccw_private *private)
 {
-	struct subchannel *sch;
-	int ret;
-
-	sch = private->sch;
 	/*
-	 * TODO:
-	 * In the cureent stage, some things like "no I/O running" and "no
-	 * interrupt pending" are clear, but we are not sure what other state
-	 * we need to care about.
-	 * There are still a lot more instructions need to be handled. We
-	 * should come back here later.
+	 * If the FSM state is seen as Not Operational after closing
+	 * and re-opening the mdev, return an error.
+	 *
+	 * Otherwise, change the FSM from STANDBY to IDLE which is
+	 * normally done by vfio_ccw_mdev_probe() in current lifecycle.
 	 */
 	vfio_ccw_fsm_event(private, VFIO_CCW_EVENT_CLOSE);
+	vfio_ccw_fsm_event(private, VFIO_CCW_EVENT_OPEN);
+	if (private->state == VFIO_CCW_STATE_NOT_OPER)
+		return -EINVAL;
 
-	ret = cio_enable_subchannel(sch, (u32)(unsigned long)sch);
-	if (!ret)
-		private->state = VFIO_CCW_STATE_IDLE;
+	private->state = VFIO_CCW_STATE_IDLE;
 
-	return ret;
+	return 0;
 }
 
 static int vfio_ccw_mdev_notifier(struct notifier_block *nb,