The command cat /proc/dma will show you what?

A.
Whether DMA is enabled

B.
Which DMA channels are in use

C.
Which DMA mode is in use

D.
General information about DMA on the machine

Explanation/Reference:
/proc/dma contains a list of the registered ISA direct memory access (DMA) channels in use. It shows whether DMA is enabled or not.

Example
# cat /proc/dma
4: cascade