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

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Date:   Tue, 8 Oct 2019 01:12:05 +0000
From:   "Justin He (Arm Technology China)" <Justin.He@....com>
To:     Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>
CC:     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-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Punit Agrawal <punitagrawal@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "hejianet@...il.com" <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()

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.


--
Cheers,
Justin (Jia He)


>       M.
> --
> Without deviation from the norm, progress is not possible.
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