DMA memory allocation support

configname: CONFIG_ZONE_DMA

Linux Kernel Configuration
└─>Processor type and features
└─>DMA memory allocation support
In linux kernel since version 2.6.21 (release Date: 2007-04-25)  
DMA memory allocation support allows devices with less than 32-bit
addressing to allocate within the first 16MB of address space.
Disable if no such devices will be used.

If unsure, say Y.