Scsi - Index of

673 * @iso_frame_desc: Used to provide arrays of ISO transfer buffers and to
674 * collect the transfer status for each buffer.
675 *
676 * This structure identifies USB transfer requests. URBs must be allocated by
677 * calling usb_alloc_urb() and freed with a call to usb_free_urb().
678 * Initialization may be done using various usb_fill_*_urb() functions. URBs
679 * are submitted using usb_submit_urb(), and pending requests may be canceled
680 * using usb_unlink_urb() or usb_kill_urb().
681 *
682 * Data Transfer Buffers:
683 *
684 * Normally drivers provide I/O buffers allocated with kmalloc() or otherwise
685 * taken from the general page pool. That is provided by transfer_buffer
686 * (control requests also use setup_packet), and host controller drivers
687 * perform a dma mapping (and unmapping) for each buffer transferred. Those
688 * mapping operations can be expensive on some platforms (perhaps using a dma
689 * bounce buffer or talking to an IOMMU),
690 * although they're cheap on commodity x86 and ppc hardware.
691 *
692 * Alternatively, drivers may pass the URB_NO_xxx_DMA_MAP transfer flags,
693 * which tell the host controller driver that no such mapping is needed since
694 * the device driver is DMA-aware. For example, a device driver might
695 * allocate a DMA buffer with usb_buffer_alloc() or call usb_buffer_map().
696 * When these transfer flags are provided, host controller drivers will
697 * attempt to use the dma addresses found in the transfer_dma and/or
698 * setup_dma fields rather than determining a dma address themselves. (Note
699 * that transfer_buffer and setup_packet must still be set because not all
700 * host controllers use DMA, nor do virtual root hubs).
701 *
66
702 * Initialization:
703 *
704 * All URBs submitted must initialize the dev, pipe, transfer_flags (may be
705 * zero), and complete fields.
706 * The URB_ASYNC_UNLINK transfer flag affects later invocations of
707 * the usb_unlink_urb() routine. Note: Failure to set URB_ASYNC_UNLINK
708 * with usb_unlink_urb() is deprecated. For synchronous unlinks use
709 * usb_kill_urb() instead.
710 *
711 * All URBs must also initialize
712 * transfer_buffer and transfer_buffer_length. They may provide the
713 * URB_SHORT_NOT_OK transfer flag, indicating that short reads are
714 * to be treated as errors; that flag is invalid for write requests.
715 *