centos man page for usb_buffer_map

USB_BUFFER_MAP(9)						   USB Core APIs						 USB_BUFFER_MAP(9)

NAME
       usb_buffer_map - create DMA mapping(s) for an urb

SYNOPSIS
       struct urb * usb_buffer_map(struct urb * urb);

ARGUMENTS
       urb
	   urb whose transfer_buffer/setup_packet will be mapped

DESCRIPTION
       URB_NO_TRANSFER_DMA_MAP is added to urb->transfer_flags if the operation succeeds. If the device is connected to this system through a
       non-DMA controller, this operation always succeeds.

       This call would normally be used for an urb which is reused, perhaps as the target of a large periodic transfer, with usb_buffer_dmasync
       calls to synchronize memory and dma state.

       Reverse the effect of this call with usb_buffer_unmap.

RETURN
       Either NULL (indicating no buffer could be mapped), or urb.

COPYRIGHT
Kernel Hackers Manual 3.10					     June 2014							 USB_BUFFER_MAP(9)