Provided by:
linux-doc-2.6.15_2.6.15-23.39_all 
NAME
struct usb_interface - what usb device drivers talk to
SYNOPSIS
struct usb_interface {
struct usb_host_interface * altsetting;
struct usb_host_interface * cur_altsetting;
unsigned num_altsetting;
int minor;
enum usb_interface_condition condition;
struct device dev;
struct class_device * class_dev;
};
MEMBERS
altsetting
array of interface structures, one for each alternate setting
that may be selected. Each one includes a set of endpoint
configurations. They will be in no particular order.
cur_altsetting
the current altsetting.
num_altsetting
number of altsettings defined.
minor the minor number assigned to this interface, if this interface
is bound to a driver that uses the USB major number. If this
interface does not use the USB major, this field should be
unused. The driver should set this value in the probe function
of the driver, after it has been assigned a minor number from
the USB core by calling usb_register_dev.
condition
binding state of the interface: not bound, binding (in probe),
bound to a driver, or unbinding (in disconnect)
dev driver model’s view of this device
class_dev
driver model’s class view of this device.
DESCRIPTION
USB device drivers attach to interfaces on a physical device. Each
interface encapsulates a single high level function, such as feeding an
audio stream to a speaker or reporting a change in a volume control.
Many USB devices only have one interface. The protocol used to talk to
an interface’s endpoints can be defined in a usb ‘‘class’’
specification, or by a product’s vendor. The (default) control endpoint
is part of every interface, but is never listed among the interface’s
descriptors.
The driver that is bound to the interface can use standard driver model
calls such as dev_get_drvdata on the dev member of this structure.
Each interface may have alternate settings. The initial configuration
of a device sets altsetting 0, but the device driver can change that
setting using usb_set_interface. Alternate settings are often used to
control the the use of periodic endpoints, such as by having different
endpoints use different amounts of reserved USB bandwidth. All
standards-conformant USB devices that use isochronous endpoints will
use them in non-default settings.
The USB specification says that alternate setting numbers must run from
0 to one less than the total number of alternate settings. But some
devices manage to mess this up, and the structures aren’t necessarily
stored in numerical order anyhow. Use usb_altnum_to_altsetting to look
up an alternate setting in the altsetting array based on its number.