Subject: Re: [PATCH v6 5/8] powerpc/pmem/of_pmem: Update of_pmem to use the new barrier instruction.

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Tue, 30 Jun 2020 10:35:12 +0530

Dan Williams <[email-masked]> writes:

> On Mon, Jun 29, 2020 at 6:58 AM Aneesh Kumar K.V
> <[email-masked]> wrote:
>>
>> of_pmem on POWER10 can now use phwsync instead of hwsync to ensure
>> all previous writes are architecturally visible for the platform
>> buffer flush.
>>
>> Signed-off-by: Aneesh Kumar K.V <[email-masked]>
>> ---
>>  arch/powerpc/include/asm/cacheflush.h | 7 +++++++
>>  1 file changed, 7 insertions(+)
>>
>> diff --git a/arch/powerpc/include/asm/cacheflush.h b/arch/powerpc/include/asm/cacheflush.h
>> index 54764c6e922d..95782f77d768 100644
>> --- a/arch/powerpc/include/asm/cacheflush.h
>> +++ b/arch/powerpc/include/asm/cacheflush.h
>> @@ -98,6 +98,13 @@ static inline void invalidate_dcache_range(unsigned long start,
>>         mb();   /* sync */
>>  }
>>
>> +#define arch_pmem_flush_barrier arch_pmem_flush_barrier
>> +static inline void  arch_pmem_flush_barrier(void)
>> +{
>> +       if (cpu_has_feature(CPU_FTR_ARCH_207S))
>> +               asm volatile(PPC_PHWSYNC ::: "memory");
>
> Shouldn't this fallback to a compatible store-fence in an else statement?

The idea was to avoid calling this on anything else. We ensure that by
making sure that pmem devices are not initialized on systems without that
cpu feature. Patch 1 does that. Also, the last patch adds a WARN_ON() to
catch the usage of this outside pmem devices and on systems without that
cpu feature.

-aneesh