linux-kernel - Re: [PATCH v10 1/3] arm64: cpufeature: introduce helper cpu_has_hw

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Message-ID: <1b28b20c-bc10-dbf6-aa78-afd985cf8920@gmail.com>
Date:   Wed, 9 Oct 2019 14:29:42 +0800
From:   Jia He <hejianet@...il.com>
To:     Suzuki K Poulose <suzuki.poulose@....com>,
        "Justin He (Arm Technology China)" <Justin.He@....com>,
        Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>
Cc:     Mark Rutland <Mark.Rutland@....com>,
        "Kaly Xin (Arm Technology China)" <Kaly.Xin@....com>,
        Catalin Marinas <Catalin.Marinas@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Matthew Wilcox <willy@...radead.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        James Morse <James.Morse@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Punit Agrawal <punitagrawal@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH v10 1/3] arm64: cpufeature: introduce helper
 cpu_has_hw_af()

Hi Suzuki

On 2019/10/8 23:32, Suzuki K Poulose wrote:
>
>
> On 08/10/2019 02:12, Justin He (Arm Technology China) wrote:
>> Hi Will and Marc
>> Sorry for the late response, just came back from a vacation.
>>
>>> -----Original Message-----
>>> From: Marc Zyngier <maz@...nel.org>
>>> Sent: 2019年10月1日 21:19
>>> To: Will Deacon <will@...nel.org>
>>> Cc: Justin He (Arm Technology China) <Justin.He@....com>; Catalin
>>> Marinas <Catalin.Marinas@....com>; Mark Rutland
>>> <Mark.Rutland@....com>; James Morse <James.Morse@....com>;
>>> Matthew Wilcox <willy@...radead.org>; Kirill A. Shutemov
>>> <kirill.shutemov@...ux.intel.com>; linux-arm-kernel@...ts.infradead.org;
>>> linux-kernel@...r.kernel.org; linux-mm@...ck.org; Punit Agrawal
>>> <punitagrawal@...il.com>; Thomas Gleixner <tglx@...utronix.de>;
>>> Andrew Morton <akpm@...ux-foundation.org>; hejianet@...il.com; Kaly
>>> Xin (Arm Technology China) <Kaly.Xin@....com>
>>> Subject: Re: [PATCH v10 1/3] arm64: cpufeature: introduce helper
>>> cpu_has_hw_af()
>>>
>>> On Tue, 1 Oct 2019 13:54:47 +0100
>>> Will Deacon <will@...nel.org> wrote:
>>>
>>>> On Mon, Sep 30, 2019 at 09:57:38AM +0800, Jia He wrote:
>>>>> We unconditionally set the HW_AFDBM capability and only enable it on
>>>>> CPUs which really have the feature. But sometimes we need to know
>>>>> whether this cpu has the capability of HW AF. So decouple AF from
>>>>> DBM by new helper cpu_has_hw_af().
>>>>>
>>>>> Signed-off-by: Jia He <justin.he@....com>
>>>>> Suggested-by: Suzuki Poulose <Suzuki.Poulose@....com>
>>>>> Reviewed-by: Catalin Marinas <catalin.marinas@....com>
>>>>> ---
>>>>>   arch/arm64/include/asm/cpufeature.h | 10 ++++++++++
>>>>>   1 file changed, 10 insertions(+)
>>>>>
>>>>> diff --git a/arch/arm64/include/asm/cpufeature.h
>>> b/arch/arm64/include/asm/cpufeature.h
>>>>> index 9cde5d2e768f..949bc7c85030 100644
>>>>> --- a/arch/arm64/include/asm/cpufeature.h
>>>>> +++ b/arch/arm64/include/asm/cpufeature.h
>>>>> @@ -659,6 +659,16 @@ static inline u32
>>> id_aa64mmfr0_parange_to_phys_shift(int parange)
>>>>>    default: return CONFIG_ARM64_PA_BITS;
>>>>>    }
>>>>>   }
>>>>> +
>>>>> +/* Check whether hardware update of the Access flag is supported */
>>>>> +static inline bool cpu_has_hw_af(void)
>>>>> +{
>>>>> + if (IS_ENABLED(CONFIG_ARM64_HW_AFDBM))
>>>>> +         return read_cpuid(ID_AA64MMFR1_EL1) & 0xf;
>>>>
>>>> 0xf? I think we should have a mask in sysreg.h for this constant.
>>>
>>> We don't have the mask, but we certainly have the shift.
>>>
>>> GENMASK(ID_AA64MMFR1_HADBS_SHIFT + 3,
>>> ID_AA64MMFR1_HADBS_SHIFT) is a bit
>>> of a mouthful though. Ideally, we'd have a helper for that.
>>>
>> Ok, I will implement the helper if there isn't so far.
>> And then replace the 0xf with it.
>
> Or could we simpl reuse existing cpuid_feature_extract_unsigned_field() ?
>
> u64 mmfr1 = read_cpuid(ID_AA64MMFR1_EL1);
>
> return cpuid_feature_extract_unsigned_field(mmfr1, ID_AA64MMFR1_HADBS_SHIFT) ?
>
Yes, we can, I will send the new version

---
Cheers,
Justin (Jia He)