CONFIG_DMA_UNCACHED_32M is not available for thedefaultarchitecture x86.
Result is shown for architecture blackfin
default or selected kernelversion does not have config value CONFIG_DMA_UNCACHED_32M.
Result is shown for kernelversion 6.7-rc3

Enable 32M DMA region

configname: CONFIG_DMA_UNCACHED_32M

Uncached DMA region
└─>Enable 32M DMA region
In linux kernel since version 3.1 (release Date: 2011-10-24)