arch/x86/platform/olpc/olpc-xo1-pm.c:159: undefined reference to `mfd_cell_disable'

[Dennis Clarke]

In 4.19.13 I was surprised to see :

ld: arch/x86/platform/olpc/olpc-xo1-pm.o: in function `xo1_pm_remove':
/usr/local/build/linux_kernel/linux-4.19.13_20190102221644/arch/x86/platform/olpc/olpc-xo1-pm.c:159: 
undefined reference to `mfd_cell_disable'
ld: arch/x86/platform/olpc/olpc-xo1-pm.o: in function `xo1_pm_probe':
/usr/local/build/linux_kernel/linux-4.19.13_20190102221644/arch/x86/platform/olpc/olpc-xo1-pm.c:133: 
undefined reference to `mfd_cell_enable'
gmake: *** [Makefile:1032: vmlinux] Error 1
Command exited with non-zero status 2

Which seems to be defined in drivers/mfd/mfd-core.c :

https://github.com/torvalds/linux/blob/6f0d349d922ba44e4348a17a78ea51b7135965b1/drivers/mfd/mfd-core.c

Seems odd given that #include <linux/mfd/core.h> is in both 
arch/x86/platform/olpc/olpc-xo1-pm.c and also 
arch/x86/platform/olpc/olpc-xo1-sci.c and not sure where the issue is 
however I have seen this twice
now. I'll hunt around and see if I can find where the issue is.

Dennis Clarke