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



NAME
       struct_usb_function - describes one function of a configuration

SYNOPSIS
       struct usb_function {
         const char * name;
         struct usb_gadget_strings ** strings;
         struct usb_descriptor_header ** fs_descriptors;
         struct usb_descriptor_header ** hs_descriptors;
         struct usb_descriptor_header ** ss_descriptors;
         struct usb_descriptor_header ** ssp_descriptors;
         struct usb_configuration * config;
         struct usb_os_desc_table * os_desc_table;
         unsigned os_desc_n;
         int (* bind) (struct usb_configuration *,struct usb_function *);
         void (* unbind) (struct usb_configuration *,struct usb_function *);
         void (* free_func) (struct usb_function *f);
         struct module * mod;
         int (* set_alt) (struct usb_function *,unsigned interface, unsigned alt);
         int (* get_alt) (struct usb_function *,unsigned interface);
         void (* disable) (struct usb_function *);
         int (* setup) (struct usb_function *,const struct usb_ctrlrequest *);
         bool (* req_match) (struct usb_function *,const struct usb_ctrlrequest *);
         void (* suspend) (struct usb_function *);
         void (* resume) (struct usb_function *);
         int (* get_status) (struct usb_function *);
         int (* func_suspend) (struct usb_function *,u8 suspend_opt);
       };

MEMBERS
       name
           For diagnostics, identifies the function.

       strings
           tables of strings, keyed by identifiers assigned during bind and by language IDs
           provided in control requests

       fs_descriptors
           Table of full (or low) speed descriptors, using interface and string identifiers
           assigned during bind(). If this pointer is null, the function will not be available at
           full speed (or at low speed).

       hs_descriptors
           Table of high speed descriptors, using interface and string identifiers assigned
           during bind(). If this pointer is null, the function will not be available at high
           speed.

       ss_descriptors
           Table of super speed descriptors, using interface and string identifiers assigned
           during bind(). If this pointer is null after initiation, the function will not be
           available at super speed.

       ssp_descriptors
           Table of super speed plus descriptors, using interface and string identifiers assigned
           during bind(). If this pointer is null after initiation, the function will not be
           available at super speed plus.

       config
           assigned when usb_add_function() is called; this is the configuration with which this
           function is associated.

       os_desc_table
           Table of (interface id, os descriptors) pairs. The function can expose more than one
           interface. If an interface is a member of an IAD, only the first interface of IAD has
           its entry in the table.

       os_desc_n
           Number of entries in os_desc_table

       bind
           Before the gadget can register, all of its functions bind to the available resources
           including string and interface identifiers used in interface or class descriptors;
           endpoints; I/O buffers; and so on.

       unbind
           Reverses bind; called as a side effect of unregistering the driver which added this
           function.

       free_func
           free the struct usb_function.

       mod
           (internal) points to the module that created this structure.

       set_alt
           (REQUIRED) Reconfigures altsettings; function drivers may initialize usb_ep.driver
           data at this time (when it is used). Note that setting an interface to its current
           altsetting resets interface state, and that all interfaces have a disabled state.

       get_alt
           Returns the active altsetting. If this is not provided, then only altsetting zero is
           supported.

       disable
           (REQUIRED) Indicates the function should be disabled. Reasons include host resetting
           or reconfiguring the gadget, and disconnection.

       setup
           Used for interface-specific control requests.

       req_match
           Tests if a given class request can be handled by this function.

       suspend
           Notifies functions when the host stops sending USB traffic.

       resume
           Notifies functions when the host restarts USB traffic.

       get_status
           Returns function status as a reply to GetStatus request when the recipient is
           Interface.

       func_suspend
           callback to be called when SetFeature(FUNCTION_SUSPEND) is reseived

DESCRIPTION
       A single USB function uses one or more interfaces, and should in most cases support
       operation at both full and high speeds. Each function is associated by usb_add_function()
       with a one configuration; that function causes bind() to be called so resources can be
       allocated as part of setting up a gadget driver. Those resources include endpoints, which
       should be allocated using usb_ep_autoconfig().

       To support dual speed operation, a function driver provides descriptors for both high and
       full speed operation. Except in rare cases that don't involve bulk endpoints, each speed
       needs different endpoint descriptors.

       Function drivers choose their own strategies for managing instance data. The simplest
       strategy just declares it "static', which means the function can only be activated once.
       If the function needs to be exposed in more than one configuration at a given speed, it
       needs to support multiple usb_function structures (one for each configuration).

       A more complex strategy might encapsulate a usb_function structure inside a
       driver-specific instance structure to allows multiple activations. An example of multiple
       activations might be a CDC ACM function that supports two or more distinct instances
       within the same configuration, providing several independent logical data links to a USB
       host.

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

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