diff --git a/hw/s390x/css.c b/hw/s390x/css.c
index c03bb20bc9..d94498a97b 100644
--- a/hw/s390x/css.c
+++ b/hw/s390x/css.c
@@ -1302,6 +1302,27 @@ bool css_schid_final(int m, uint8_t cssid, uint8_t ssid, uint16_t schid)
                                  (MAX_SCHID + 1) / sizeof(unsigned long));
 }
 
+unsigned int css_find_free_chpid(uint8_t cssid)
+{
+    CssImage *css = channel_subsys.css[cssid];
+    unsigned int chpid;
+
+    if (!css) {
+        return MAX_CHPID + 1;
+    }
+
+    for (chpid = 0; chpid <= MAX_CHPID; chpid++) {
+        /* skip reserved chpid */
+        if (chpid == VIRTIO_CCW_CHPID) {
+            continue;
+        }
+        if (!css->chpids[chpid].in_use) {
+            return chpid;
+        }
+    }
+    return MAX_CHPID + 1;
+}
+
 static int css_add_virtual_chpid(uint8_t cssid, uint8_t chpid, uint8_t type)
 {
     CssImage *css;
diff --git a/include/hw/s390x/css.h b/include/hw/s390x/css.h
index f1f0d7f07a..e61fa74d9b 100644
--- a/include/hw/s390x/css.h
+++ b/include/hw/s390x/css.h
@@ -28,6 +28,7 @@
 #define MAX_CIWS 62
 
 #define VIRTUAL_CSSID 0xfe
+#define VIRTIO_CCW_CHPID 0   /* used by convention */
 
 typedef struct CIW {
     uint8_t type;
@@ -115,6 +116,7 @@ bool css_devno_used(uint8_t cssid, uint8_t ssid, uint16_t devno);
 void css_subch_assign(uint8_t cssid, uint8_t ssid, uint16_t schid,
                       uint16_t devno, SubchDev *sch);
 void css_sch_build_virtual_schib(SubchDev *sch, uint8_t chpid, uint8_t type);
+unsigned int css_find_free_chpid(uint8_t cssid);
 uint16_t css_build_subchannel_id(SubchDev *sch);
 void css_reset(void);
 void css_reset_sch(SubchDev *sch);