Only in /usr/glenda/nusb/serial: cdc.c
diff -ur /sys/src/cmd/nusb/serial/mkfile /usr/glenda/nusb/serial/mkfile
--- /sys/src/cmd/nusb/serial/mkfile	Fri Dec 13 00:31:34 2019
+++ /usr/glenda/nusb/serial/mkfile	Mon Jun  8 18:00:33 2020
@@ -1,7 +1,7 @@
 </$objtype/mkfile
 
 TARG=serial
-OFILES=ftdi.$O serial.$O prolific.$O ucons.$O silabs.$O ch340.$O
+OFILES=ftdi.$O serial.$O prolific.$O ucons.$O silabs.$O ch340.$O cdc.$O
 HFILES=\
 	../lib/usb.h\
 	serial.h\
diff -ur /sys/src/cmd/nusb/serial/serial.c /usr/glenda/nusb/serial/serial.c
--- /sys/src/cmd/nusb/serial/serial.c	Fri Dec 13 00:31:34 2019
+++ /usr/glenda/nusb/serial/serial.c	Wed Jun 10 21:36:54 2020
@@ -621,9 +621,12 @@
 {
 	int i, epin, epout, epintr;
 	Ep *ep, **eps;
+	int oifc;
 
+	oifc = ifc;
 	epintr = epin = epout = -1;
 
+TOPFINDEPS:
 	/*
 	 * interfc 0 means start from the start which is equiv to
 	 * iterate through endpoints probably, could be done better
@@ -644,8 +647,13 @@
 		}
 	}
 	dprint(2, "serial[%d]: ep ids: in %d out %d intr %d\n", ifc, epin, epout, epintr);
-	if(epin == -1 || epout == -1 || (ser->hasepintr && epintr == -1))
-		return -1;
+	if(epin == -1 || epout == -1 || (ser->hasepintr && epintr == -1)){
+		ifc++;
+		if(ifc > 1)
+			return -1;
+		goto TOPFINDEPS;
+	}
+	ifc = oifc;
 
 	if(openeps(&ser->p[ifc], epin, epout, epintr) < 0)
 		return -1;
@@ -714,6 +722,7 @@
 extern int slprobe(Serial *ser);
 extern int chprobe(Serial *ser);
 extern int uconsprobe(Serial *ser);
+extern int cdcprobe(Serial *ser);
 
 void
 threadmain(int argc, char* argv[])
@@ -750,7 +759,8 @@
 	&& ftprobe(ser)
 	&& slprobe(ser)
 	&& plprobe(ser)
-	&& chprobe(ser))
+	&& chprobe(ser)
+	&& cdcprobe(ser))
 		sysfatal("no serial devices found");
 
 	for(i = 0; i < ser->nifcs; i++){