Matteo,
[quote user="Matteo Mattei"]When this type of issue occurs, even reloading the module we are not able to recover the printer and we are forced to issue a powercycle. [/quote]
The musb module reset is not in the musb driver, but in usb_musb_pm_init() in arch/arm/mach-omap2/usb-musb.c. So if it is a lockup happened in the controller not the phy, reloading the drivers will not reset the controller.
The question is whether the issue (controller lockup?) generated by ESD in the lab is the same as that happened in the field...