CONFIG_DMA_UNCACHED_2M is not available for thedefaultarchitecture x86.
Result is shown for architecture blackfin
default or selected kernelversion does not have config value CONFIG_DMA_UNCACHED_2M.
Result is shown for kernelversion 6.7-rc3

Enable 2M DMA region

configname: CONFIG_DMA_UNCACHED_2M

Uncached DMA region
└─>Enable 2M DMA region
In linux kernel since version 2.6.24 (release Date: 2008-01-24)