STRUCT USB_FUNCTION(9) Kernel Mode Gadget API STRUCT USB_FUNCTION(9)NAMEstruct_usb_function - describes one function of a configuration
SYNOPSIS
struct usb_function {
const char * name;
struct usb_gadget_strings ** strings;
struct usb_descriptor_header ** descriptors;
struct usb_descriptor_header ** hs_descriptors;
struct usb_configuration * config;
int (* bind) (struct usb_configuration *,struct usb_function *);
void (* unbind) (struct usb_configuration *,struct usb_function *);
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 *);
void (* suspend) (struct usb_function *);
void (* resume) (struct usb_function *);
};
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
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.
config
assigned when usb_add_function() is called; this is the
configuration with which this function is associated.
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.
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.
suspend
Notifies functions when the host stops sending USB traffic.
resume
Notifies functions when the host restarts USB traffic.
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@users.sourceforge.net>
Author.
COPYRIGHTKernel Hackers Manual 2.6. November 2013 STRUCT USB_FUNCTION(9)
