struct_usb_interface (9)

struct usb_interface {
  struct usb_host_interface * altsetting;
  struct usb_host_interface * cur_altsetting;
  unsigned num_altsetting;
  struct usb_interface_assoc_descriptor * intf_assoc;
  int minor;
  enum usb_interface_condition condition;
  unsigned sysfs_files_created:1;
  unsigned ep_devs_created:1;
  unsigned unregistering:1;
  unsigned needs_remote_wakeup:1;
  unsigned needs_altsetting0:1;
  unsigned needs_binding:1;
  unsigned reset_running:1;
  unsigned resetting_device:1;
  struct device dev;
  struct device * usb_dev;
  atomic_t pm_usage_cnt;
  struct work_struct reset_ws;
};

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.

intf_assoc

interface association descriptor

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)

sysfs_files_created

sysfs attributes exist

ep_devs_created

endpoint child pseudo-devices exist

unregistering

flag set when the interface is being unregistered

needs_remote_wakeup

flag set when the driver requires remote-wakeup capability during autosuspend.

needs_altsetting0

flag set when a set-interface request for altsetting 0 has been deferred.

needs_binding

flag set when the driver should be re-probed or unbound following a reset or suspend operation it doesn't support.

reset_running

set to 1 if the interface is currently running a queued reset so that usb_cancel_queued_reset doesn't try to remove from the workqueue when running inside the worker thread. See __usb_queue_reset_device.

resetting_device

USB core reset the device, so use alt setting 0 as current; needs bandwidth alloc after reset.

dev

driver model's view of this device

usb_dev

if an interface is bound to the USB major, this will point to the sysfs representation for that device.

pm_usage_cnt

PM usage counter for this interface

reset_ws

Used for scheduling resets from atomic context.

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 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.