diff --git a/include/hw/s390x/css.h b/include/hw/s390x/css.h
index 08ad1a1..666ce11 100644
--- a/include/hw/s390x/css.h
+++ b/include/hw/s390x/css.h
@@ -136,11 +136,22 @@
     /* transport-provided data: */
     int (*ccw_cb) (SubchDev *, CCW1);
     void (*disable_cb)(SubchDev *);
-    int (*do_subchannel_work) (SubchDev *);
+    IOInstEnding (*do_subchannel_work) (SubchDev *);
     SenseId id;
     void *driver_data;
 };
 
+static inline void sch_gen_unit_exception(SubchDev *sch)
+{
+    sch->curr_status.scsw.ctrl &= ~SCSW_ACTL_START_PEND;
+    sch->curr_status.scsw.ctrl |= SCSW_STCTL_PRIMARY |
+                                  SCSW_STCTL_SECONDARY |
+                                  SCSW_STCTL_ALERT |
+                                  SCSW_STCTL_STATUS_PEND;
+    sch->curr_status.scsw.cpa = sch->channel_prog + 8;
+    sch->curr_status.scsw.dstat =  SCSW_DSTAT_UNIT_EXCEP;
+}
+
 extern const VMStateDescription vmstate_subch_dev;
 
 /*
@@ -199,9 +210,9 @@
 void css_generate_chp_crws(uint8_t cssid, uint8_t chpid);
 void css_generate_css_crws(uint8_t cssid);
 void css_clear_sei_pending(void);
-int s390_ccw_cmd_request(ORB *orb, SCSW *scsw, void *data);
-int do_subchannel_work_virtual(SubchDev *sub);
-int do_subchannel_work_passthrough(SubchDev *sub);
+IOInstEnding s390_ccw_cmd_request(SubchDev *sch);
+IOInstEnding do_subchannel_work_virtual(SubchDev *sub);
+IOInstEnding do_subchannel_work_passthrough(SubchDev *sub);
 
 typedef enum {
     CSS_IO_ADAPTER_VIRTIO = 0,
@@ -232,7 +243,7 @@
 int css_do_xsch(SubchDev *sch);
 int css_do_csch(SubchDev *sch);
 int css_do_hsch(SubchDev *sch);
-int css_do_ssch(SubchDev *sch, ORB *orb);
+IOInstEnding css_do_ssch(SubchDev *sch, ORB *orb);
 int css_do_tsch_get_irb(SubchDev *sch, IRB *irb, int *irb_len);
 void css_do_tsch_update_subch(SubchDev *sch);
 int css_do_stcrw(CRW *crw);
@@ -243,7 +254,7 @@
 void css_do_schm(uint8_t mbk, int update, int dct, uint64_t mbo);
 int css_enable_mcsse(void);
 int css_enable_mss(void);
-int css_do_rsch(SubchDev *sch);
+IOInstEnding css_do_rsch(SubchDev *sch);
 int css_do_rchp(uint8_t cssid, uint8_t chpid);
 bool css_present(uint8_t cssid);
 #endif