1STRUCT USB_FUNCTION(9)      Kernel Mode Gadget API      STRUCT USB_FUNCTION(9)
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NAME

6       struct_usb_function - describes one function of a configuration
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SYNOPSIS

9       struct usb_function {
10         const char * name;
11         struct usb_gadget_strings ** strings;
12         struct usb_descriptor_header ** descriptors;
13         struct usb_descriptor_header ** hs_descriptors;
14         struct usb_configuration * config;
15         int (* bind) (struct usb_configuration *,struct usb_function *);
16         void (* unbind) (struct usb_configuration *,struct usb_function *);
17         int (* set_alt) (struct usb_function *,unsigned interface, unsigned alt);
18         int (* get_alt) (struct usb_function *,unsigned interface);
19         void (* disable) (struct usb_function *);
20         int (* setup) (struct usb_function *,const struct usb_ctrlrequest *);
21         void (* suspend) (struct usb_function *);
22         void (* resume) (struct usb_function *);
23       };
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MEMBERS

26       name
27           For diagnostics, identifies the function.
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29       strings
30           tables of strings, keyed by identifiers assigned during bind and by
31           language IDs provided in control requests
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33       descriptors
34           Table of full (or low) speed descriptors, using interface and
35           string identifiers assigned during bind(). If this pointer is null,
36           the function will not be available at full speed (or at low speed).
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38       hs_descriptors
39           Table of high speed descriptors, using interface and string
40           identifiers assigned during bind(). If this pointer is null, the
41           function will not be available at high speed.
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43       config
44           assigned when usb_add_function() is called; this is the
45           configuration with which this function is associated.
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47       bind
48           Before the gadget can register, all of its functions bind to the
49           available resources including string and interface identifiers used
50           in interface or class descriptors; endpoints; I/O buffers; and so
51           on.
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53       unbind
54           Reverses bind; called as a side effect of unregistering the driver
55           which added this function.
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57       set_alt
58           (REQUIRED) Reconfigures altsettings; function drivers may
59           initialize usb_ep.driver data at this time (when it is used). Note
60           that setting an interface to its current altsetting resets
61           interface state, and that all interfaces have a disabled state.
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63       get_alt
64           Returns the active altsetting. If this is not provided, then only
65           altsetting zero is supported.
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67       disable
68           (REQUIRED) Indicates the function should be disabled. Reasons
69           include host resetting or reconfiguring the gadget, and
70           disconnection.
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72       setup
73           Used for interface-specific control requests.
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75       suspend
76           Notifies functions when the host stops sending USB traffic.
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78       resume
79           Notifies functions when the host restarts USB traffic.
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DESCRIPTION

82       A single USB function uses one or more interfaces, and should in most
83       cases support operation at both full and high speeds. Each function is
84       associated by usb_add_function() with a one configuration; that
85       function causes bind() to be called so resources can be allocated as
86       part of setting up a gadget driver. Those resources include endpoints,
87       which should be allocated using usb_ep_autoconfig().
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89       To support dual speed operation, a function driver provides descriptors
90       for both high and full speed operation. Except in rare cases that don´t
91       involve bulk endpoints, each speed needs different endpoint
92       descriptors.
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94       Function drivers choose their own strategies for managing instance
95       data. The simplest strategy just declares it "static´, which means the
96       function can only be activated once. If the function needs to be
97       exposed in more than one configuration at a given speed, it needs to
98       support multiple usb_function structures (one for each configuration).
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100       A more complex strategy might encapsulate a usb_function structure
101       inside a driver-specific instance structure to allows multiple
102       activations. An example of multiple activations might be a CDC ACM
103       function that supports two or more distinct instances within the same
104       configuration, providing several independent logical data links to a
105       USB host.
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AUTHOR

108       David Brownell <dbrownell@users.sourceforge.net>
109           Author.
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112Kernel Hackers Manual 2.6.         June 2019            STRUCT USB_FUNCTION(9)
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