diff --git a/lib/s390x/css_lib.c b/lib/s390x/css_lib.c
new file mode 100644
index 0000000..dc5a512
--- /dev/null
+++ b/lib/s390x/css_lib.c
@@ -0,0 +1,70 @@
+/*
+ * Channel Subsystem tests library
+ *
+ * Copyright (c) 2020 IBM Corp
+ *
+ * Authors:
+ *  Pierre Morel <pmorel@linux.ibm.com>
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2.
+ */
+#include <libcflat.h>
+#include <alloc_phys.h>
+#include <asm/page.h>
+#include <string.h>
+#include <interrupt.h>
+#include <asm/arch_def.h>
+
+#include <css.h>
+
+static struct schib schib;
+
+/*
+ * css_enumerate:
+ * On success return the first subchannel ID found.
+ * On error return an invalid subchannel ID containing cc
+ */
+int css_enumerate(void)
+{
+	struct pmcw *pmcw = &schib.pmcw;
+	int scn_found = 0;
+	int dev_found = 0;
+	int schid = 0;
+	int cc;
+	int scn;
+
+	for (scn = 0; scn < 0xffff; scn++) {
+		cc = stsch(scn | SCHID_ONE, &schib);
+		switch (cc) {
+		case 0:		/* 0 means SCHIB stored */
+			break;
+		case 3:		/* 3 means no more channels */
+			goto out;
+		default:	/* 1 or 2 should never happened for STSCH */
+			report_info("Unexpected error %d on subchannel %08x",
+				    cc, scn | SCHID_ONE);
+			return cc;
+		}
+
+		/* We currently only support type 0, a.k.a. I/O channels */
+		if (PMCW_CHANNEL_TYPE(pmcw) != 0)
+			continue;
+
+		/* We ignore I/O channels without valid devices */
+		scn_found++;
+		if (!(pmcw->flags & PMCW_DNV))
+			continue;
+
+		/* We keep track of the first device as our test device */
+		if (!schid)
+			schid = scn | SCHID_ONE;
+		report_info("Found subchannel %08x", scn | SCHID_ONE);
+		dev_found++;
+	}
+
+out:
+	report_info("Tested subchannels: %d, I/O subchannels: %d, I/O devices: %d",
+		    scn, scn_found, dev_found);
+	return schid;
+}
diff --git a/s390x/Makefile b/s390x/Makefile
index 3cb97da..afd2c9b 100644
--- a/s390x/Makefile
+++ b/s390x/Makefile
@@ -17,6 +17,7 @@ tests += $(TEST_DIR)/stsi.elf
 tests += $(TEST_DIR)/skrf.elf
 tests += $(TEST_DIR)/smp.elf
 tests += $(TEST_DIR)/sclp.elf
+tests += $(TEST_DIR)/css.elf
 tests_binary = $(patsubst %.elf,%.bin,$(tests))
 
 all: directories test_cases test_cases_binary
@@ -53,6 +54,7 @@ cflatobjs += lib/s390x/mmu.o
 cflatobjs += lib/s390x/smp.o
 cflatobjs += lib/s390x/kernel-args.o
 cflatobjs += lib/s390x/css_dump.o
+cflatobjs += lib/s390x/css_lib.o
 
 OBJDIRS += lib/s390x
 
diff --git a/s390x/css.c b/s390x/css.c
new file mode 100644
index 0000000..f0e8f47
--- /dev/null
+++ b/s390x/css.c
@@ -0,0 +1,64 @@
+/*
+ * Channel Subsystem tests
+ *
+ * Copyright (c) 2020 IBM Corp
+ *
+ * Authors:
+ *  Pierre Morel <pmorel@linux.ibm.com>
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2.
+ */
+
+#include <libcflat.h>
+#include <alloc_phys.h>
+#include <asm/page.h>
+#include <string.h>
+#include <interrupt.h>
+#include <asm/arch_def.h>
+
+#include <css.h>
+
+static int test_device_sid;
+
+static void test_enumerate(void)
+{
+	test_device_sid = css_enumerate();
+	if (test_device_sid & SCHID_ONE) {
+		report(1, "First device schid: 0x%08x", test_device_sid);
+		return;
+	}
+
+	switch (test_device_sid) {
+	case 0:
+		report (0, "No I/O device found");
+		break;
+	default:	/* 1 or 2 should never happened for STSCH */
+		report(0, "Unexpected cc=%d during enumeration",
+		       test_device_sid);
+			return;
+	}
+}
+
+static struct {
+	const char *name;
+	void (*func)(void);
+} tests[] = {
+	{ "enumerate (stsch)", test_enumerate },
+	{ NULL, NULL }
+};
+
+int main(int argc, char *argv[])
+{
+	int i;
+
+	report_prefix_push("Channel Subsystem");
+	for (i = 0; tests[i].name; i++) {
+		report_prefix_push(tests[i].name);
+		tests[i].func();
+		report_prefix_pop();
+	}
+	report_prefix_pop();
+
+	return report_summary();
+}
diff --git a/s390x/unittests.cfg b/s390x/unittests.cfg
index b307329..0f156af 100644
--- a/s390x/unittests.cfg
+++ b/s390x/unittests.cfg
@@ -84,3 +84,7 @@ extra_params = -m 1G
 [sclp-3g]
 file = sclp.elf
 extra_params = -m 3G
+
+[css]
+file = css.elf
+extra_params = -device virtio-net-ccw
