Build issue has been identified when COMPILE_TEST=y and MFD_STM32_TIMERS=n:
https://lkml.org/lkml/2018/5/17/825
- First patch introduces a stub routine in mfd header file
- Sub-sequent patch solves warning in pwm-stm32 with these configs

Fabrice Gasnier (2):
  mfd: stm32-timers: fix pwm-stm32 linker issue with COMPILE_TEST
  pwm: stm32: initialize raw local variables

 drivers/pwm/pwm-stm32.c          |  2 +-
 include/linux/mfd/stm32-timers.h | 12 ++++++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

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1.9.1