This panic seems to be wrong. Without it usb can be used in virtual box (the propietary version) without problems.

Reference: /n/sources/patch/applied/ohcipanic
Date: Mon Jan 17 17:35:13 CET 2011
Signed-off-by: paurea@lsub.org

--- /sys/src/9/pc/usbohci.c	Mon Jan 17 17:32:43 2011
+++ /sys/src/9/pc/usbohci.c	Mon Jan 17 17:32:07 2011
@@ -229,7 +229,7 @@
 struct Td
 {
 	ulong	ctrl;
-	ulong	cbp;
+	ulong	cbp;		/* current buffer pointer */
 	ulong	nexttd;
 	ulong	be;
 	ushort	offsets[8];	/* used by Iso Tds only */
@@ -1134,8 +1134,6 @@
 	switch(err){
 	case Tddataovr:			/* Overrun is not an error */
 	case Tdok:
-		if(td->cbp != 0)
-			panic("ohci: full packet but cbp != 0");
 		break;
 	case Tddataund:
 		/* short input packets are ok */