nVidia added support for KMS in their driver version 361.28.
so the configuration for KMS with a nvidia driver will depend on whether you have a legacy graphic card and use a driver with a lower version.
About Nvidia 340, KMS, framebuffer
https://forums.gentoo.org/viewtopic-p-7977618.html
See also:
http://linux.overshoot.tv/wiki/kernel_mode_setting
New kernel module source layout for NVIDIA Linux kernel modules
https://devtalk.nvidia.com/default/topic/856253/unix-graphics-announceme...
