[SOLVED] linux kernel compilation: ERROR: "function" [path/to/module/module.ko] undefined

Issue

I have a similar problem to this one, only for me it's an error not a warning. I'm building linux-4.8.5 with a patch applied to one module. I get:

ERROR: "intel_soc_pmic_readb" [drivers/gpu/drm/i915/i915.ko] undefined!
ERROR: "intel_soc_pmic_writeb" [drivers/gpu/drm/i915/i915.ko] undefined!
scripts/Makefile.modpost:91: recipe for target '__modpost' failed
make[1]: *** [__modpost] Error 1
Makefile:1201: recipe for target 'modules' failed
make: *** [modules] Error 2

In the other question they say something about KBUILD_EXTRA_SYMBOLS and documentation is supposed to be in Documentation/kbuild/modules.txt. But reading this file, this seems only to apply to modules not included in linux itself?

The functions are defined like

int function(){
    do_stuff;
}
EXPORT_SYMBOL(function);

then there is the declaration

 int function();

in a .h file in the include folder and it's called like

 #include <the_aforementioned_file.h>
//stuff
function();

from a file in the same folder as the definition of the function. There are no other occurrences of the function name in the whole source tree.

And I really just don't see the mistake. Most likely I'm not looking in the right place, I guess.

Solution

As explained in a comment by Tsyvarev, this error is caused because the module in question is not being built, it requires the option CONFIG_INTEL_SOC_PMIC.

Answered By - Nobody