CONFIG_ATARI_MIDI is not available for thedefaultarchitecture x86.
Result is shown for architecture m68k
default or selected kernelversion does not have config value CONFIG_ATARI_MIDI.
Result is shown for kernelversion 6.2.5

Atari MIDI serial support

configname: CONFIG_ATARI_MIDI

Linux Kernel Configuration
└─>Character devices
└─>Atari MIDI serial support
In linux kernel since version 2.6.12  
If you want to use your Atari's MIDI port in Linux, say Y.

To compile this driver as a module, choose M here.