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SubjectRe: [PATCH v2] powerpc/mm: Add mask of always present MMU features
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Le 21/10/2020 à 16:25, Aneesh Kumar K.V a écrit :
> Christophe Leroy <christophe.leroy@csgroup.eu> writes:
>
>> Le 12/10/2020 à 17:39, Christophe Leroy a écrit :
>>> On the same principle as commit 773edeadf672 ("powerpc/mm: Add mask
>>> of possible MMU features"), add mask for MMU features that are
>>> always there in order to optimise out dead branches.
>>>
>>> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
>>> ---
>>> v2: Features must be anded with MMU_FTRS_POSSIBLE instead of ~0, otherwise
>>> MMU_FTRS_ALWAYS is ~0 when no #ifdef matches.
>>
>> This is still not enough. For BOOK3S/32, MMU_FTRS_POSSIBLE is still too much.
>> We need a #ifdef CONFIG_PPC_BOOK3S_32 with 0.
>>
>> Christophe
>>
>>> ---
>>> arch/powerpc/include/asm/mmu.h | 25 +++++++++++++++++++++++++
>>> 1 file changed, 25 insertions(+)
>>>
>>> diff --git a/arch/powerpc/include/asm/mmu.h b/arch/powerpc/include/asm/mmu.h
>>> index 255a1837e9f7..64e7e7f7cda9 100644
>>> --- a/arch/powerpc/include/asm/mmu.h
>>> +++ b/arch/powerpc/include/asm/mmu.h
>>> @@ -201,8 +201,30 @@ enum {
>>> 0,
>>> };
>>>
>>> +enum {
>>> + MMU_FTRS_ALWAYS =
>>> +#ifdef CONFIG_PPC_8xx
>>> + MMU_FTR_TYPE_8xx &
>>> +#endif
>>> +#ifdef CONFIG_40x
>>> + MMU_FTR_TYPE_40x &
>>> +#endif
>>> +#ifdef CONFIG_PPC_47x
>>> + MMU_FTR_TYPE_47x &
>>> +#elif defined(CONFIG_44x)
>>> + MMU_FTR_TYPE_44x &
>>> +#endif
>>> +#if defined(CONFIG_E200) || defined(CONFIG_E500)
>>> + MMU_FTR_TYPE_FSL_E &
>>> +#endif
>>> + MMU_FTRS_POSSIBLE,
>>> +};
>
> Will it be simpler if we make it a #define like below?
>
> #ifdef CONFIG_PPC_8XX
> #define MMU_FTR_ALWAYS MMU_FTR_TYPE_8XX & MMU_FTR_POSSIBLE
> #endif

Yes you are right, it will be simpler, and consistant with CPU_FTR_ALWAYS which is partly set with
defines after all.

Christophe

>
>
>
>>> +
>>> static inline bool early_mmu_has_feature(unsigned long feature)
>>> {
>>> + if (MMU_FTRS_ALWAYS & feature)
>>> + return true;
>>> +
>>> return !!(MMU_FTRS_POSSIBLE & cur_cpu_spec->mmu_features & feature);
>>> }
>>>
>>> @@ -231,6 +253,9 @@ static __always_inline bool mmu_has_feature(unsigned long feature)
>>> }
>>> #endif
>>>
>>> + if (MMU_FTRS_ALWAYS & feature)
>>> + return true;
>>> +
>>> if (!(MMU_FTRS_POSSIBLE & feature))
>>> return false;
>>>
>>>

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