|USB_BUFFER_MAP(9)||USB Core APIs||USB_BUFFER_MAP(9)|
usb_buffer_map - create DMA mapping(s) for an urb
struct urb * usb_buffer_map(struct urb * urb);
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.
Either NULL (indicating no buffer could be mapped), or urb.
|January 2017||Kernel Hackers Manual 4.8.|