@Keitaro While opening the complete setup to build matching kernel modules is definitely something @onion should do (@administrators, @Lazar-Demin, hello again…), there's a ugly workaround for this: you can just force the module to load:
This is not without risk - if kernel internals have changed too much between the kernel you are running and the kernel the module has been compiled for, this will crash the system or cause any other undefined behaviour.
Having said that, the kernel APIs used by kmod-gpio-irq haven't changed between kernels 4.4.46 and 4.4.71, so it should work in this case.
@Boken-Lin Thanks - had already found this. I think some of my issues to date have been to do with my mistakes in building kernel code using the OenWRT cross compilation - I think I had some settings wrong. Am in the process of trying again with git://git.openwrt.org/15.05/openwrt.git - will let you know how things go.