Re: [RFC PATCH 5/7] arm64: smp: use generic SMP stop common code

[Cristian Marussi]

Hi

On 8/26/19 4:32 PM, Christoph Hellwig wrote:
> > +config ARCH_USE_COMMON_SMP_STOP
> > +	def_bool y if SMP
>
> The option belongs into common code and the arch code shoud only
> select it.

In fact that was my first approach, but then I noticed that in kernel/ topdir
there was no generic Kconfig but only subsystem specific ones:

Kconfig.freezer  Kconfig.hz       Kconfig.locks    Kconfig.preempt

while instead looking into archs top level Kconfig, beside the usual arch/Kconfig selects,
I could find this similar sort of "reversed" approach in which the arch defined and
selected a CONFIG which was indeed then used only in common code like in:

20:37 $ egrep -R ARCH_HAS_CACHE_LINE_SIZE .
./arch/arc/Kconfig:config ARCH_HAS_CACHE_LINE_SIZE
./arch/x86/Kconfig:config ARCH_HAS_CACHE_LINE_SIZE
./arch/arm64/Kconfig:config ARCH_HAS_CACHE_LINE_SIZE
./include/linux/cache.h:#ifndef CONFIG_ARCH_HAS_CACHE_LINE_SIZE

20:39 $ egrep -R ARCH_HAS_KEXEC_PURGATORY .
./arch/powerpc/Kconfig:config ARCH_HAS_KEXEC_PURGATORY
./arch/x86/Kconfig:config ARCH_HAS_KEXEC_PURGATORY
./arch/s390/Kconfig:config ARCH_HAS_KEXEC_PURGATORY
./arch/s390/purgatory/Makefile:obj-$(CONFIG_ARCH_HAS_KEXEC_PURGATORY) += kexec-purgatory.o
./arch/s390/Kbuild:obj-$(CONFIG_ARCH_HAS_KEXEC_PURGATORY) += purgatory/
./kernel/kexec_file.c:	if (!IS_ENABLED(CONFIG_ARCH_HAS_KEXEC_PURGATORY))

so I thought it was an acceptable option and I went for it, not to introduce a new kernel/Kconfig.smp
just for this new config option; but in fact I could have missed the real reason underlying these two
different choices.

Thanks

Cristian