setup a scatterlist for DMA input
| fifo, |
| || sgl, |
| || nents, |
| || len|
address of the fifo to be used
pointer to the scatterlist array
number of entries in the scatterlist array
number of elements to transfer
This macro fills a scatterlist for DMA input.
It returns the number entries in the scatterlist array.
Note that with only one concurrent reader and one concurrent
writer, you don't need extra locking to use these macros.