Chapter 5. USB Core APIs
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Chapter 5. USB Core APIs

Table of Contents

usb_init_urb - initializes a urb so that it can be used by a USB driver
usb_alloc_urb - creates a new urb for a USB driver to use
usb_free_urb - frees the memory used by a urb when all users of it are finished
usb_get_urb - increments the reference count of the urb
usb_submit_urb - issue an asynchronous transfer request for an endpoint
usb_unlink_urb - abort/cancel a transfer request for an endpoint
usb_kill_urb - cancel a transfer request and wait for it to finish
usb_control_msg - Builds a control urb, sends it off and waits for completion
usb_bulk_msg - Builds a bulk urb, sends it off and waits for completion
usb_sg_init - initializes scatterlist-based bulk/interrupt I/O request
usb_sg_wait - synchronously execute scatter/gather request
usb_sg_cancel - stop scatter/gather i/o issued by usb_sg_wait
usb_get_descriptor - issues a generic GET_DESCRIPTOR request
usb_string - returns ISO 8859-1 version of a string descriptor
usb_get_status - issues a GET_STATUS call
usb_clear_halt - tells device to clear endpoint halt/stall condition
usb_set_interface - Makes a particular alternate setting be current
usb_reset_configuration - lightweight device reset
usb_register_dev - register a USB device, and ask for a minor number
usb_deregister_dev - deregister a USB device's dynamic minor.
usb_match_id - find first usb_device_id matching device or interface
usb_register_driver - register a USB driver
usb_deregister - unregister a USB driver
usb_ifnum_to_if - get the interface object with a given interface number
usb_altnum_to_altsetting - get the altsetting structure with a given
usb_driver_claim_interface - bind a driver to an interface
usb_driver_release_interface - unbind a driver from an interface
usb_find_interface - find usb_interface pointer for driver and device
usb_alloc_dev - usb device constructor (usbcore-internal)
usb_get_dev - increments the reference count of the usb device structure
usb_put_dev - release a use of the usb device structure
usb_get_intf - increments the reference count of the usb interface structure
usb_put_intf - release a use of the usb interface structure
usb_lock_device_for_reset - cautiously acquire the lock for a
usb_find_device - find a specific usb device in the system
usb_get_current_frame_number - return current bus frame number
usb_buffer_alloc - allocate dma-consistent buffer for URB_NO_xxx_DMA_MAP
usb_buffer_free - free memory allocated with usb_buffer_alloc
usb_buffer_map - create DMA mapping(s) for an urb
usb_buffer_dmasync - synchronize DMA and CPU view of buffer(s)
usb_buffer_unmap - free DMA mapping(s) for an urb
usb_buffer_map_sg - create scatterlist DMA mapping(s) for an endpoint
usb_buffer_dmasync_sg - synchronize DMA and CPU view of scatterlist buffer(s)
usb_buffer_unmap_sg - free DMA mapping(s) for a scatterlist
usb_hub_tt_clear_buffer - clear control/bulk TT state in high speed hub
usb_set_device_state - change a device's current state (usbcore, hcds)
usb_root_hub_lost_power - called by HCD if the root hub lost Vbus power
usb_disconnect - disconnect a device (usbcore-internal)
usb_reset_device - perform a USB port reset to reinitialize a device

There are two basic I/O models in the USB API. The most elemental one is asynchronous: drivers submit requests in the form of an URB, and the URB's completion callback handle the next step. All USB transfer types support that model, although there are special cases for control URBs (which always have setup and status stages, but may not have a data stage) and isochronous URBs (which allow large packets and include per-packet fault reports). Built on top of that is synchronous API support, where a driver calls a routine that allocates one or more URBs, submits them, and waits until they complete. There are synchronous wrappers for single-buffer control and bulk transfers (which are awkward to use in some driver disconnect scenarios), and for scatterlist based streaming i/o (bulk or interrupt).

USB drivers need to provide buffers that can be used for DMA, although they don't necessarily need to provide the DMA mapping themselves. There are APIs to use used when allocating DMA buffers, which can prevent use of bounce buffers on some systems. In some cases, drivers may be able to rely on 64bit DMA to eliminate another kind of bounce buffer.

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struct usb_sg_request Home usb_init_urb