The last couple of custom compiles of new kernels on my server have failed to get the attached Arduino up and running again, due to failure of configure to compile in the FTDI driver even though it was compiled in previous version.
My process is:
Download and untar the source.
make mrproper
copy .config from old kernel source (where ftdi was compiled in and working) to new
make menuconfig and lazily don't bother to check, just save, compile and install, reboot.
All seems good except that Arduino is not working.
Check USB devices in kernel and lo and behold FTDI driver is not compiled in.
Check it off, recompile and install, all good.
So problem resolved ok, but I must be missing something in the .config file - maybe that config param gets renamed every time and so is not recognized?