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1======================2FunctionFS Descriptors3======================4 5Some of the descriptors that can be written to the FFS gadget are6described below. Device and configuration descriptors are handled7by the composite gadget and are not written by the user to the8FFS gadget.9 10Descriptors are written to the "ep0" file in the FFS gadget11following the descriptor header.12 13.. kernel-doc:: include/uapi/linux/usb/functionfs.h14 :doc: descriptors15 16Interface Descriptors17---------------------18 19Standard USB interface descriptors may be written. The class/subclass of the20most recent interface descriptor determines what type of class-specific21descriptors are accepted.22 23Class-Specific Descriptors24--------------------------25 26Class-specific descriptors are accepted only for the class/subclass of the27most recent interface descriptor. The following are some of the28class-specific descriptors that are supported.29 30DFU Functional Descriptor31~~~~~~~~~~~~~~~~~~~~~~~~~32 33When the interface class is USB_CLASS_APP_SPEC and the interface subclass34is USB_SUBCLASS_DFU, a DFU functional descriptor can be provided.35The DFU functional descriptor is a described in the USB specification for36Device Firmware Upgrade (DFU), version 1.1 as of this writing.37 38.. kernel-doc:: include/uapi/linux/usb/functionfs.h39 :doc: usb_dfu_functional_descriptor40