stupid question

[Adam Myrow]

You have to do "make dep" any time you change your configuration, or
any time you "make clean."  Same goes for "make mrproper."  BTW: what I do
is to copy my .config to another place outside the kernel source tree once
I get a stable kernel.  Then, when I want to build a new kernel, I put the
.config back, do a "make oldconfig," and the rest of the steps.  It makes
life easier both for upgrades and recompiles of an existing version.  I
back up .config again each time I upgrade or change something, of course.