Re: [PATCH] powerpc: add compile-time support for lbarx, lwarx

[Nicholas Piggin <npiggin@gmail.com>]

Excerpts from Christophe Leroy's message of November 7, 2020 6:15 pm:
> 
> 
> Le 07/11/2020 à 04:23, Nicholas Piggin a écrit :
>> ISA v2.06 (POWER7 and up) as well as e6500 support lbarx and lwarx.
>> Add a compile option that allows code to use it, and add support in
>> cmpxchg and xchg 8 and 16 bit values.
> 
> Do you mean lharx ? Because lwarx exists on all powerpcs I think.

Thanks all who pointed out mistakes :) Yes lharx.

> 
>> 
>> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
>> ---
>>   arch/powerpc/Kconfig                   |   3 +
>>   arch/powerpc/include/asm/cmpxchg.h     | 236 ++++++++++++++++++++++++-
>>   arch/powerpc/platforms/Kconfig.cputype |   5 +
>>   3 files changed, 243 insertions(+), 1 deletion(-)
>> 
>> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
>> index e9f13fe08492..d231af06f75a 100644
>> --- a/arch/powerpc/Kconfig
>> +++ b/arch/powerpc/Kconfig
>> @@ -266,6 +266,9 @@ config PPC_BARRIER_NOSPEC
>>   	default y
>>   	depends on PPC_BOOK3S_64 || PPC_FSL_BOOK3E
>>   
>> +config PPC_LBARX_LWARX
>> +	bool
> 
> s/LWARX/LHARX/ ?
> 
> And maybe better with PPC_HAS_LBARX_LWARX ?

Yes you're right, PPC_HAS_ fits better.

[...]

>> +#endif
> 
> That's a lot of code duplication. Could we use some macro, in the same spirit as what is done in 
> arch/powerpc/include/asm/io.h for in_be16(), in_be32(), in_be64() and friends ?

For now I don't get too fancy. It's a bit ugly but I'm working through a 
generic atomics conversion patch and trying to also work out a nice form
for larx/stcx operation generation macros, I'll look at tidying up this
some time after then.

Thanks,
Nick