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
7

SYNOPSIS

9       struct usb_function {
10         const char * name;
11         struct usb_gadget_strings ** strings;
12         struct usb_descriptor_header ** fs_descriptors;
13         struct usb_descriptor_header ** hs_descriptors;
14         struct usb_descriptor_header ** ss_descriptors;
15         struct usb_configuration * config;
16         int (* bind) (struct usb_configuration *,struct usb_function *);
17         void (* unbind) (struct usb_configuration *,struct usb_function *);
18         void (* free_func) (struct usb_function *f);
19         struct module * mod;
20         int (* set_alt) (struct usb_function *,unsigned interface, unsigned alt);
21         int (* get_alt) (struct usb_function *,unsigned interface);
22         void (* disable) (struct usb_function *);
23         int (* setup) (struct usb_function *,const struct usb_ctrlrequest *);
24         void (* suspend) (struct usb_function *);
25         void (* resume) (struct usb_function *);
26         int (* get_status) (struct usb_function *);
27         int (* func_suspend) (struct usb_function *,u8 suspend_opt);
28       };
29

MEMBERS

31       name
32           For diagnostics, identifies the function.
33
34       strings
35           tables of strings, keyed by identifiers assigned during bind and by
36           language IDs provided in control requests
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38       fs_descriptors
39           Table of full (or low) speed descriptors, using interface and
40           string identifiers assigned during bind(). If this pointer is null,
41           the function will not be available at full speed (or at low speed).
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43       hs_descriptors
44           Table of high speed descriptors, using interface and string
45           identifiers assigned during bind(). If this pointer is null, the
46           function will not be available at high speed.
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48       ss_descriptors
49           Table of super speed descriptors, using interface and string
50           identifiers assigned during bind(). If this pointer is null after
51           initiation, the function will not be available at super speed.
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53       config
54           assigned when usb_add_function() is called; this is the
55           configuration with which this function is associated.
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57       bind
58           Before the gadget can register, all of its functions bind to the
59           available resources including string and interface identifiers used
60           in interface or class descriptors; endpoints; I/O buffers; and so
61           on.
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63       unbind
64           Reverses bind; called as a side effect of unregistering the driver
65           which added this function.
66
67       free_func
68           free the struct usb_function.
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70       mod
71           (internal) points to the module that created this structure.
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73       set_alt
74           (REQUIRED) Reconfigures altsettings; function drivers may
75           initialize usb_ep.driver data at this time (when it is used). Note
76           that setting an interface to its current altsetting resets
77           interface state, and that all interfaces have a disabled state.
78
79       get_alt
80           Returns the active altsetting. If this is not provided, then only
81           altsetting zero is supported.
82
83       disable
84           (REQUIRED) Indicates the function should be disabled. Reasons
85           include host resetting or reconfiguring the gadget, and
86           disconnection.
87
88       setup
89           Used for interface-specific control requests.
90
91       suspend
92           Notifies functions when the host stops sending USB traffic.
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94       resume
95           Notifies functions when the host restarts USB traffic.
96
97       get_status
98           Returns function status as a reply to GetStatus request when the
99           recepient is Interface.
100
101       func_suspend
102           callback to be called when SetFeature(FUNCTION_SUSPEND) is reseived
103

DESCRIPTION

105       A single USB function uses one or more interfaces, and should in most
106       cases support operation at both full and high speeds. Each function is
107       associated by usb_add_function() with a one configuration; that
108       function causes bind() to be called so resources can be allocated as
109       part of setting up a gadget driver. Those resources include endpoints,
110       which should be allocated using usb_ep_autoconfig().
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112       To support dual speed operation, a function driver provides descriptors
113       for both high and full speed operation. Except in rare cases that don't
114       involve bulk endpoints, each speed needs different endpoint
115       descriptors.
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117       Function drivers choose their own strategies for managing instance
118       data. The simplest strategy just declares it "static', which means the
119       function can only be activated once. If the function needs to be
120       exposed in more than one configuration at a given speed, it needs to
121       support multiple usb_function structures (one for each configuration).
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123       A more complex strategy might encapsulate a usb_function structure
124       inside a driver-specific instance structure to allows multiple
125       activations. An example of multiple activations might be a CDC ACM
126       function that supports two or more distinct instances within the same
127       configuration, providing several independent logical data links to a
128       USB host.
129

AUTHOR

131       David Brownell <dbrownell@users.sourceforge.net>
132           Author.
133

135Kernel Hackers Manual 3.10         June 2019            STRUCT USB_FUNCTION(9)
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