struct_usb_gadget (9)

struct usb_gadget {
  struct work_struct work;
  const struct usb_gadget_ops * ops;
  struct usb_ep * ep0;
  struct list_head ep_list;
  enum usb_device_speed speed;
  enum usb_device_speed max_speed;
  enum usb_device_state state;
  const char * name;
  struct device dev;
  unsigned out_epnum;
  unsigned in_epnum;
  unsigned sg_supported:1;
  unsigned is_otg:1;
  unsigned is_a_peripheral:1;
  unsigned b_hnp_enable:1;
  unsigned a_hnp_support:1;
  unsigned a_alt_hnp_support:1;
  unsigned quirk_ep_out_aligned_size:1;
};

work

(internal use) Workqueue to be used for sysfs_notify

ops

Function pointers used to access hardware-specific operations.

ep0

Endpoint zero, used when reading or writing responses to driver setup requests

ep_list

List of other endpoints supported by the device.

speed

Speed of current connection to USB host.

max_speed

Maximal speed the UDC can handle. UDC must support this and all slower speeds.

state

the state we are now (attached, suspended, configured, etc)

name

Identifies the controller hardware type. Used in diagnostics and sometimes configuration.

dev

Driver model state for this abstract device.

out_epnum

last used out ep number

in_epnum

last used in ep number

sg_supported

true if we can handle scatter-gather

is_otg

True if the USB device port uses a Mini-AB jack, so that the gadget driver must provide a USB OTG descriptor.

is_a_peripheral

False unless is_otg, the “A” end of a USB cable is in the Mini-AB jack, and HNP has been used to switch roles so that the “A” device currently acts as A-Peripheral, not A-Host.

b_hnp_enable

OTG device feature flag, indicating that the A-Host enabled HNP support.

a_hnp_support

OTG device feature flag, indicating that the A-Host supports HNP at this port.

a_alt_hnp_support

OTG device feature flag, indicating that the A-Host only supports HNP on a different root port.

quirk_ep_out_aligned_size

epout requires buffer size to be aligned to MaxPacketSize.

Gadgets have a mostly-portable “gadget driver” implementing device functions, handling all usb configurations and interfaces. Gadget drivers talk to hardware-specific code indirectly, through ops vectors. That insulates the gadget driver from hardware details, and packages the hardware endpoints through generic i/o queues. The “usb_gadget” and “usb_ep” interfaces provide that insulation from the hardware.

Except for the driver data, all fields in this structure are read-only to the gadget driver. That driver data is part of the “driver model” infrastructure in 2.6 (and later) kernels, and for earlier systems is grouped in a similar structure that's not known to the rest of the kernel.

Values of the three OTG device feature flags are updated before the setup call corresponding to USB_REQ_SET_CONFIGURATION, and before driver suspend calls. They are valid only when is_otg, and when the device is acting as a B-Peripheral (so is_a_peripheral is false).

David Brownell <[email protected]>

Author.