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From:   Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Subject: Re: [PATCH v4 05/10] powerpc/dt_cpu_ftrs: Add feature for 2nd DAWR
To:     Jordan Niethe <jniethe5@gmail.com>
Cc:     Michael Ellerman <mpe@ellerman.id.au>, mikey@neuling.org,
        apopple@linux.ibm.com, Paul Mackerras <paulus@samba.org>,
        Nicholas Piggin <npiggin@gmail.com>,
        Christophe Leroy <christophe.leroy@c-s.fr>,
        naveen.n.rao@linux.vnet.ibm.com, peterz@infradead.org,
        jolsa@kernel.org, oleg@redhat.com, fweisbec@gmail.com,
        mingo@kernel.org, pedromfc@br.ibm.com, miltonm@us.ibm.com,
        linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
        Ravi Bangoria <ravi.bangoria@linux.ibm.com>
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Date:   Tue, 21 Jul 2020 13:21:16 +0530
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On 7/17/20 11:14 AM, Jordan Niethe wrote:
> On Fri, Jul 17, 2020 at 2:10 PM Ravi Bangoria
> <ravi.bangoria@linux.ibm.com> wrote:
>>
>> Add new device-tree feature for 2nd DAWR. If this feature is present,
>> 2nd DAWR is supported, otherwise not.
>>
>> Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
>> ---
>>   arch/powerpc/include/asm/cputable.h | 7 +++++--
>>   arch/powerpc/kernel/dt_cpu_ftrs.c   | 7 +++++++
>>   2 files changed, 12 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/powerpc/include/asm/cputable.h b/arch/powerpc/include/asm/cputable.h
>> index e506d429b1af..3445c86e1f6f 100644
>> --- a/arch/powerpc/include/asm/cputable.h
>> +++ b/arch/powerpc/include/asm/cputable.h
>> @@ -214,6 +214,7 @@ static inline void cpu_feature_keys_init(void) { }
>>   #define CPU_FTR_P9_TLBIE_ERAT_BUG      LONG_ASM_CONST(0x0001000000000000)
>>   #define CPU_FTR_P9_RADIX_PREFETCH_BUG  LONG_ASM_CONST(0x0002000000000000)
>>   #define CPU_FTR_ARCH_31                        LONG_ASM_CONST(0x0004000000000000)
>> +#define CPU_FTR_DAWR1                  LONG_ASM_CONST(0x0008000000000000)
>>
>>   #ifndef __ASSEMBLY__
>>
>> @@ -497,14 +498,16 @@ static inline void cpu_feature_keys_init(void) { }
>>   #define CPU_FTRS_POSSIBLE      \
>>              (CPU_FTRS_POWER7 | CPU_FTRS_POWER8E | CPU_FTRS_POWER8 | \
>>               CPU_FTR_ALTIVEC_COMP | CPU_FTR_VSX_COMP | CPU_FTRS_POWER9 | \
>> -            CPU_FTRS_POWER9_DD2_1 | CPU_FTRS_POWER9_DD2_2 | CPU_FTRS_POWER10)
>> +            CPU_FTRS_POWER9_DD2_1 | CPU_FTRS_POWER9_DD2_2 | CPU_FTRS_POWER10 | \
>> +            CPU_FTR_DAWR1)
>>   #else
>>   #define CPU_FTRS_POSSIBLE      \
>>              (CPU_FTRS_PPC970 | CPU_FTRS_POWER5 | \
>>               CPU_FTRS_POWER6 | CPU_FTRS_POWER7 | CPU_FTRS_POWER8E | \
>>               CPU_FTRS_POWER8 | CPU_FTRS_CELL | CPU_FTRS_PA6T | \
>>               CPU_FTR_VSX_COMP | CPU_FTR_ALTIVEC_COMP | CPU_FTRS_POWER9 | \
>> -            CPU_FTRS_POWER9_DD2_1 | CPU_FTRS_POWER9_DD2_2 | CPU_FTRS_POWER10)
>> +            CPU_FTRS_POWER9_DD2_1 | CPU_FTRS_POWER9_DD2_2 | CPU_FTRS_POWER10 | \
>> +            CPU_FTR_DAWR1)
> Instead of putting CPU_FTR_DAWR1 into CPU_FTRS_POSSIBLE should it go
> into CPU_FTRS_POWER10?
> Then it will be picked up by CPU_FTRS_POSSIBLE.

I remember a discussion about this with Mikey and we decided to do it
this way. Obviously, the purpose is to make CPU_FTR_DAWR1 independent of
CPU_FTRS_POWER10 because DAWR1 is an optional feature in p10. I fear
including CPU_FTR_DAWR1 in CPU_FTRS_POWER10 can make it forcefully enabled
even when device-tree property is not present or pa-feature bit it not set,
because we do:

       {       /* 3.1-compliant processor, i.e. Power10 "architected" mode */
               .pvr_mask               = 0xffffffff,
               .pvr_value              = 0x0f000006,
               .cpu_name               = "POWER10 (architected)",
               .cpu_features           = CPU_FTRS_POWER10,

>>   #endif /* CONFIG_CPU_LITTLE_ENDIAN */
>>   #endif
>>   #else
>> diff --git a/arch/powerpc/kernel/dt_cpu_ftrs.c b/arch/powerpc/kernel/dt_cpu_ftrs.c
>> index ac650c233cd9..c78cd3596ec4 100644
>> --- a/arch/powerpc/kernel/dt_cpu_ftrs.c
>> +++ b/arch/powerpc/kernel/dt_cpu_ftrs.c
>> @@ -574,6 +574,12 @@ static int __init feat_enable_mma(struct dt_cpu_feature *f)
>>          return 1;
>>   }
>>
>> +static int __init feat_enable_debug_facilities_v31(struct dt_cpu_feature *f)
>> +{
>> +       cur_cpu_spec->cpu_features |= CPU_FTR_DAWR1;
>> +       return 1;
>> +}
>> +
>>   struct dt_cpu_feature_match {
>>          const char *name;
>>          int (*enable)(struct dt_cpu_feature *f);
>> @@ -649,6 +655,7 @@ static struct dt_cpu_feature_match __initdata
>>          {"wait-v3", feat_enable, 0},
>>          {"prefix-instructions", feat_enable, 0},
>>          {"matrix-multiply-assist", feat_enable_mma, 0},
>> +       {"debug-facilities-v31", feat_enable_debug_facilities_v31, 0},
> Since all feat_enable_debug_facilities_v31() does is set
> CPU_FTR_DAWR1, if you just have:
> {"debug-facilities-v31", feat_enable, CPU_FTR_DAWR1},
> I think cpufeatures_process_feature() should set it in for you at this point:
>              if (m->enable(f)) {
>                  cur_cpu_spec->cpu_features |= m->cpu_ftr_bit_mask;
>                  break;
>              }

Yes, that seems a better option.

Thanks,
Ravi