Re: [PATCH 1/2] powerpc/64: Move CPU -mtune options into Kconfig

[Michael Ellerman <mpe@ellerman.id.au>]

Nathan Chancellor <nathan@kernel.org> writes:
> On Fri, Mar 03, 2023 at 12:16:55AM +1100, Michael Ellerman wrote:
>> Currently the -mtune options are set in the Makefile, depending on what
>> is the compiler supports.
>> 
>> One downside of doing it that way is that the chosen -mtune option is
>> not recorded in the .config.
>> 
>> Another downside is that doing more complicated logic to calculate the
>> correct option gets messy in the Makefile.
>> 
>> So move the determination of which -mtune option to use into Kconfig
>> logic.
>> 
>> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
>
> Reviewed-by: Nathan Chancellor <nathan@kernel.org>
>
>> ---
>>  arch/powerpc/Makefile                  | 4 +---
>>  arch/powerpc/platforms/Kconfig.cputype | 6 ++++++
>>  2 files changed, 7 insertions(+), 3 deletions(-)
>> 
>> diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
>> index 87d6ac27eebd..779956007f0c 100644
>> --- a/arch/powerpc/Makefile
>> +++ b/arch/powerpc/Makefile
>> @@ -156,9 +156,7 @@ endif
>>  CFLAGS-$(CONFIG_TARGET_CPU_BOOL) += -mcpu=$(CONFIG_TARGET_CPU)
>>  AFLAGS-$(CONFIG_TARGET_CPU_BOOL) += -mcpu=$(CONFIG_TARGET_CPU)
>>  
>> -CFLAGS-$(CONFIG_POWERPC64_CPU) += $(call cc-option,-mtune=power10,	\
>> -				  $(call cc-option,-mtune=power9,	\
>> -				  $(call cc-option,-mtune=power8)))
>> +CFLAGS-y += $(CONFIG_TUNE_CPU)
>>  
>>  asinstr := $(call as-instr,lis 9$(comma)foo@high,-DHAVE_AS_ATHIGH=1)
>>  
>> diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
>> index 046b571496b1..7d7477b73951 100644
>> --- a/arch/powerpc/platforms/Kconfig.cputype
>> +++ b/arch/powerpc/platforms/Kconfig.cputype
>> @@ -273,6 +273,12 @@ config TARGET_CPU
>>  	default "e500mc" if E500MC_CPU
>>  	default "powerpc" if POWERPC_CPU
>>  
>> +config TUNE_CPU
>> +	string
>> +	default "-mtune=power10" if POWERPC64_CPU && CC_IS_GCC   && $(cc-option,-mtune=power10)
>> +	default "-mtune=power9"  if POWERPC64_CPU && CC_IS_GCC   && $(cc-option,-mtune=power9)
>> +	default "-mtune=power8"  if POWERPC64_CPU && CC_IS_GCC   && $(cc-option,-mtune=power8)
>
> Would it be cleaner to hoist the POWERPC64_CPU dependency?

I was experimenting with some follow-on patches that add more cases for
other CPUs, but that got messy and it'll need a bit more work.

So for now yes I should just hoist that dependency.

cheers

> config TUNE_CPU
> 	string
> 	default "-mtune=power10" if CC_IS_GCC   && $(cc-option,-mtune=power10)
> 	default "-mtune=power9"  if CC_IS_GCC   && $(cc-option,-mtune=power9)
> 	default "-mtune=power8"  if CC_IS_GCC   && $(cc-option,-mtune=power8)
> 	depends on POWERPC64_CPU