linux-kernel - Re: [PATCH 2/4] arm64: cpufeature: add feature for CRC32 instructions

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Message-ID: <CAKv+Gu-tM9aKZJ3ppt9yLVP_V5YA_yN8D1j_-NtM+qQCdnc6JA@mail.gmail.com>
Date:   Tue, 28 Aug 2018 20:43:35 +0200
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Will Deacon <will.deacon@....com>
Cc:     linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@...r.kernel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Eric Biggers <ebiggers@...gle.com>,
        "Suzuki K. Poulose" <suzuki.poulose@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/4] arm64: cpufeature: add feature for CRC32 instructions

On 28 August 2018 at 19:01, Will Deacon <will.deacon@....com> wrote:
> On Mon, Aug 27, 2018 at 01:02:43PM +0200, Ard Biesheuvel wrote:
>> Add a CRC32 feature bit and wire it up to the CPU id register so we
>> will be able to use alternatives patching for CRC32 operations.
>>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
>> ---
>>  arch/arm64/include/asm/cpucaps.h | 3 ++-
>>  arch/arm64/kernel/cpufeature.c   | 9 +++++++++
>>  2 files changed, 11 insertions(+), 1 deletion(-)
>
> Acked-by: Will Deacon <will.deacon@....com>
>
> With the minor caveat below...
>
>> diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h
>> index ae1f70450fb2..9932aca9704b 100644
>> --- a/arch/arm64/include/asm/cpucaps.h
>> +++ b/arch/arm64/include/asm/cpucaps.h
>> @@ -51,7 +51,8 @@
>>  #define ARM64_SSBD                           30
>>  #define ARM64_MISMATCHED_CACHE_TYPE          31
>>  #define ARM64_HAS_STAGE2_FWB                 32
>> +#define ARM64_HAS_CRC32                              33
>>
>> -#define ARM64_NCAPS                          33
>> +#define ARM64_NCAPS                          34
>
>
> ... if this goes via crypto, you'll almost certainly get a (trivial)
> conflict with arm64, since these numbers get bumped all the time.
>

I think the first three patches should go through the arm64 tree. The
last one just removes the now redundant crc32 SIMD driver, and Herbert
could pick that up separately, i.e., it should be totally independent.


>>  #endif /* __ASM_CPUCAPS_H */
>> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
>> index e238b7932096..7626b80128f5 100644
>> --- a/arch/arm64/kernel/cpufeature.c
>> +++ b/arch/arm64/kernel/cpufeature.c
>> @@ -1222,6 +1222,15 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
>>               .cpu_enable = cpu_enable_hw_dbm,
>>       },
>>  #endif
>> +     {
>> +             .desc = "CRC32 instructions",
>> +             .capability = ARM64_HAS_CRC32,
>> +             .type = ARM64_CPUCAP_SYSTEM_FEATURE,
>> +             .matches = has_cpuid_feature,
>> +             .sys_reg = SYS_ID_AA64ISAR0_EL1,
>> +             .field_pos = ID_AA64ISAR0_CRC32_SHIFT,
>> +             .min_field_value = 1,
>> +     },
>>       {},
>>  };
>>
>> --
>> 2.18.0
>>