Provided by: linux-doc-2.6.15_2.6.15-23.39_all
usb_buffer_map_sg - create scatterlist DMA mapping(s) for an endpoint
int usb_buffer_map_sg (struct usb_device * dev, unsigned pipe,
struct scatterlist * sg, int nents);
dev device to which the scatterlist will be mapped
pipe endpoint defining the mapping direction
sg the scatterlist to map
nents the number of entries in the scatterlist
Return value is either < 0 (indicating no buffers could be mapped), or
the number of DMA mapping array entries in the scatterlist.
The caller is responsible for placing the resulting DMA addresses from
the scatterlist into URB transfer buffer pointers, and for setting the
URB_NO_TRANSFER_DMA_MAP transfer flag in each of those URBs.
Top I/O rates come from queuing URBs, instead of waiting for each one
to complete before starting the next I/O. This is particularly easy to
do with scatterlists. Just allocate and submit one URB for each DMA
mapping entry returned, stopping on the first error or when all
succeed. Better yet, use the usb_sg_*() calls, which do that (and more)
This call would normally be used when translating scatterlist requests,
rather than usb_buffer_map, since on some hardware (with IOMMUs) it may
be able to coalesce mappings for improved I/O efficiency.
Reverse the effect of this call with usb_buffer_unmap_sg.