usb_buffer_map (9) - Linux Man Pages
usb_buffer_map: create DMA mapping(s) for an urb
usb_buffer_map - create DMA mapping(s) for an urb
struct urb * usb_buffer_map(struct urb
- urb whose transfer_buffer/setup_packet will be mapped
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.