STRUCT USB_GADGET_DR(9)               Kernel Mode Gadget API              STRUCT USB_GADGET_DR(9)



NAME
       struct_usb_gadget_driver - driver for usb 'slave' devices

SYNOPSIS
       struct usb_gadget_driver {
         char * function;
         enum usb_device_speed max_speed;
         int (* bind) (struct usb_gadget *gadget,struct usb_gadget_driver *driver);
         void (* unbind) (struct usb_gadget *);
         int (* setup) (struct usb_gadget *,const struct usb_ctrlrequest *);
         void (* disconnect) (struct usb_gadget *);
         void (* suspend) (struct usb_gadget *);
         void (* resume) (struct usb_gadget *);
         void (* reset) (struct usb_gadget *);
         struct device_driver driver;
         char * udc_name;
         struct list_head pending;
         unsigned match_existing_only:1;
       };

MEMBERS
       function
           String describing the gadget's function

       max_speed
           Highest speed the driver handles.

       bind
           the driver's bind callback

       unbind
           Invoked when the driver is unbound from a gadget, usually from rmmod (after a
           disconnect is reported). Called in a context that permits sleeping.

       setup
           Invoked for ep0 control requests that aren't handled by the hardware level driver.
           Most calls must be handled by the gadget driver, including descriptor and
           configuration management. The 16 bit members of the setup data are in USB byte order.
           Called in_interrupt; this may not sleep. Driver queues a response to ep0, or returns
           negative to stall.

       disconnect
           Invoked after all transfers have been stopped, when the host is disconnected. May be
           called in_interrupt; this may not sleep. Some devices can't detect disconnect, so this
           might not be called except as part of controller shutdown.

       suspend
           Invoked on USB suspend. May be called in_interrupt.

       resume
           Invoked on USB resume. May be called in_interrupt.

       reset
           Invoked on USB bus reset. It is mandatory for all gadget drivers and should be called
           in_interrupt.

       driver
           Driver model state for this driver.

       udc_name
           A name of UDC this driver should be bound to. If udc_name is NULL, this driver will be
           bound to any available UDC.

       pending
           UDC core private data used for deferred probe of this driver.

       match_existing_only
           If udc is not found, return an error and don't add this gadget driver to list of
           pending driver

DESCRIPTION
       Devices are disabled till a gadget driver successfully binds, which means the driver will
       handle setup requests needed to enumerate (and meet “chapter 9” requirements) then do some
       useful work.

       If gadget->is_otg is true, the gadget driver must provide an OTG descriptor during
       enumeration, or else fail the bind call. In such cases, no USB traffic may flow until both
       bind returns without having called usb_gadget_disconnect, and the USB host stack has
       initialized.

       Drivers use hardware-specific knowledge to configure the usb hardware. endpoint addressing
       is only one of several hardware characteristics that are in descriptors the ep0
       implementation returns from setup calls.

       Except for ep0 implementation, most driver code shouldn't need change to run on top of
       different usb controllers. It'll use endpoints set up by that ep0 implementation.

       The usb controller driver handles a few standard usb requests. Those include set_address,
       and feature flags for devices, interfaces, and endpoints (the get_status, set_feature, and
       clear_feature requests).

       Accordingly, the driver's setup callback must always implement all get_descriptor
       requests, returning at least a device descriptor and a configuration descriptor. Drivers
       must make sure the endpoint descriptors match any hardware constraints. Some hardware also
       constrains other descriptors. (The pxa250 allows only configurations 1, 2, or 3).

       The driver's setup callback must also implement set_configuration, and should also
       implement set_interface, get_configuration, and get_interface. Setting a configuration (or
       interface) is where endpoints should be activated or (config 0) shut down.

       (Note that only the default control endpoint is supported. Neither hosts nor devices
       generally support control traffic except to ep0.)

       Most devices will ignore USB suspend/resume operations, and so will not provide those
       callbacks. However, some may need to change modes when the host is not longer directing
       those activities. For example, local controls (buttons, dials, etc) may need to be
       re-enabled since the (remote) host can't do that any longer; or an error state might be
       cleared, to make the device behave identically whether or not power is maintained.

AUTHOR
       David Brownell <dbrownell AT users.net>
           Author.

COPYRIGHT
Kernel Hackers Manual 4.8.                 January 2017                   STRUCT USB_GADGET_DR(9)