Ok, not that trivial...
The problem is more like POWER_SUPPLY should be a bool, not a tristate.
If you think about it: you don't want things like nouveau to depend on a random subsystem like that, people will never get it. In fact, POWER_SUPPLY provides empty inline stubs when not enabled, so that's really designed to not have depends...
However that -cannot- work if POWER_SUPPLY is modular and the drivers who use it are not. The only fixes here that make sense I can think of that don't also involve Kconfig horrors are:
Ugly: in power_supply.h, use the extern variant if
defined(CONFIG_POWER_SUPPLY) || (defined(CONFIG_POWER_SUPPLY_MODULE) && defined(MODULE))
IE. use the stub if power supply is a module and what is being built is built-in. Of course that's not only ugly, it somewhat sucks from a user perspective as the subsystem now exists but can't be used by some drivers...
- Better: Just make the bloody thing a bool :-) The power supply
framework itself is small enough, just make it a boolean option and avoid the problem entirely. The actual power supply sub drivers can remain modular of course.
We can just do select POWER_SUPPLY.
Yes it reduces the option range for some stupid corner case but really I don't care, removing features from the kernel that a driver depends on is just leading to insane state combination and QA problems.
Dave.