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SubjectRe: [PATCH] powerpc/features: Remove CPU_FTR_NODSISRALIGN
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"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> writes:
> On 10/13/20 3:45 PM, Michael Ellerman wrote:
>> Christophe Leroy <christophe.leroy@csgroup.eu> writes:
>>> Le 13/10/2020 à 09:23, Aneesh Kumar K.V a écrit :
>>>> Christophe Leroy <christophe.leroy@csgroup.eu> writes:
>>>>
>>>>> CPU_FTR_NODSISRALIGN has not been used since
>>>>> commit 31bfdb036f12 ("powerpc: Use instruction emulation
>>>>> infrastructure to handle alignment faults")
>>>>>
>>>>> Remove it.
>>>>>
>>>>> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
>>>>> ---
>>>>> arch/powerpc/include/asm/cputable.h | 22 ++++++++++------------
>>>>> arch/powerpc/kernel/dt_cpu_ftrs.c | 8 --------
>>>>> arch/powerpc/kernel/prom.c | 2 +-
>>>>> 3 files changed, 11 insertions(+), 21 deletions(-)
>>>>>
>>>>> diff --git a/arch/powerpc/kernel/dt_cpu_ftrs.c b/arch/powerpc/kernel/dt_cpu_ftrs.c
>>>>> index 1098863e17ee..c598961d9f15 100644
>>>>> --- a/arch/powerpc/kernel/dt_cpu_ftrs.c
>>>>> +++ b/arch/powerpc/kernel/dt_cpu_ftrs.c
>>>>> @@ -273,13 +273,6 @@ static int __init feat_enable_idle_nap(struct dt_cpu_feature *f)
>>>>> return 1;
>>>>> }
>>>>>
>>>>> -static int __init feat_enable_align_dsisr(struct dt_cpu_feature *f)
>>>>> -{
>>>>> - cur_cpu_spec->cpu_features &= ~CPU_FTR_NODSISRALIGN;
>>>>> -
>>>>> - return 1;
>>>>> -}
>>>>> -
>>>>> static int __init feat_enable_idle_stop(struct dt_cpu_feature *f)
>>>>> {
>>>>> u64 lpcr;
>>>>> @@ -641,7 +634,6 @@ static struct dt_cpu_feature_match __initdata
>>>>> {"tm-suspend-hypervisor-assist", feat_enable, CPU_FTR_P9_TM_HV_ASSIST},
>>>>> {"tm-suspend-xer-so-bug", feat_enable, CPU_FTR_P9_TM_XER_SO_BUG},
>>>>> {"idle-nap", feat_enable_idle_nap, 0},
>>>>> - {"alignment-interrupt-dsisr", feat_enable_align_dsisr, 0},
>>
>> Rather than removing it entirely, I'd rather we left a comment, so that
>> it's obvious that we are ignoring that feature on purpose, not because
>> we forget about it.
>>
>> eg:
>>
>> diff --git a/arch/powerpc/kernel/dt_cpu_ftrs.c b/arch/powerpc/kernel/dt_cpu_ftrs.c
>> index f204ad79b6b5..45cb7e59bd13 100644
>> --- a/arch/powerpc/kernel/dt_cpu_ftrs.c
>> +++ b/arch/powerpc/kernel/dt_cpu_ftrs.c
>> @@ -640,7 +640,7 @@ static struct dt_cpu_feature_match __initdata
>> {"tm-suspend-hypervisor-assist", feat_enable, CPU_FTR_P9_TM_HV_ASSIST},
>> {"tm-suspend-xer-so-bug", feat_enable, CPU_FTR_P9_TM_XER_SO_BUG},
>> {"idle-nap", feat_enable_idle_nap, 0},
>> - {"alignment-interrupt-dsisr", feat_enable_align_dsisr, 0},
>> + // "alignment-interrupt-dsisr" ignored
>> {"idle-stop", feat_enable_idle_stop, 0},
>> {"machine-check-power8", feat_enable_mce_power8, 0},
>> {"performance-monitor-power8", feat_enable_pmu_power8, 0},
>>
>
>
> why not do it as
> static int __init feat_enable_align_dsisr(struct dt_cpu_feature *f)
> {
> /* This feature should not be enabled */
> #ifdef DEBUG
> WARN(1);
> #endif
>
> return 1;
> }

No one will ever turn that #define on.
No one will ever turn the feature on either.
Even if they did, it's not a bug because the kernel doesn't use the
DSISR for alignment interrupts any more.

All I want is to be able to compare the list of features defined in
skiboot vs the ones in Linux and see that none are missing in Linux.

cheers

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