linux-kernel - RE: [PATCH v8 1/3] arm64: cpufeature: introduce helper cpu_has_hw

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Message-ID: <DB7PR08MB3082C58131C4CBAF88B939D1F7840@DB7PR08MB3082.eurprd08.prod.outlook.com>
Date:   Tue, 24 Sep 2019 01:50:24 +0000
From:   "Justin He (Arm Technology China)" <Justin.He@....com>
To:     Catalin Marinas <Catalin.Marinas@....com>
CC:     Will Deacon <will@...nel.org>, Mark Rutland <Mark.Rutland@....com>,
        James Morse <James.Morse@....com>,
        Marc Zyngier <maz@...nel.org>,
        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>,
        Suzuki Poulose <Suzuki.Poulose@....com>,
        Punit Agrawal <punitagrawal@...il.com>,
        Anshuman Khandual <Anshuman.Khandual@....com>,
        Alex Van Brunt <avanbrunt@...dia.com>,
        Robin Murphy <Robin.Murphy@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jérôme Glisse <jglisse@...hat.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        "hejianet@...il.com" <hejianet@...il.com>,
        "Kaly Xin (Arm Technology China)" <Kaly.Xin@....com>,
        nd <nd@....com>
Subject: RE: [PATCH v8 1/3] arm64: cpufeature: introduce helper
 cpu_has_hw_af()

Hi Catalin

> -----Original Message-----
> From: Catalin Marinas <catalin.marinas@....com>
> Sent: 2019年9月24日 0:07
> To: Justin He (Arm Technology China) <Justin.He@....com>
> Cc: Will Deacon <will@...nel.org>; Mark Rutland
> <Mark.Rutland@....com>; James Morse <James.Morse@....com>; Marc
> Zyngier <maz@...nel.org>; 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; Suzuki Poulose <Suzuki.Poulose@....com>; Punit
> Agrawal <punitagrawal@...il.com>; Anshuman Khandual
> <Anshuman.Khandual@....com>; Alex Van Brunt
> <avanbrunt@...dia.com>; Robin Murphy <Robin.Murphy@....com>;
> Thomas Gleixner <tglx@...utronix.de>; Andrew Morton <akpm@...ux-
> foundation.org>; Jérôme Glisse <jglisse@...hat.com>; Ralph Campbell
> <rcampbell@...dia.com>; hejianet@...il.com; Kaly Xin (Arm Technology
> China) <Kaly.Xin@....com>; nd <nd@....com>
> Subject: Re: [PATCH v8 1/3] arm64: cpufeature: introduce helper
> cpu_has_hw_af()
> 
> On Sat, Sep 21, 2019 at 09:50:52PM +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().
> >
> > Reported-by: kbuild test robot <lkp@...el.com>
> > Suggested-by: Suzuki Poulose <Suzuki.Poulose@....com>
> > Signed-off-by: Jia He <justin.he@....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 c96ffa4722d3..46caf934ba4e 100644
> > --- a/arch/arm64/include/asm/cpufeature.h
> > +++ b/arch/arm64/include/asm/cpufeature.h
> > @@ -667,6 +667,16 @@ static inline u32
> id_aa64mmfr0_parange_to_phys_shift(int parange)
> >  	default: return CONFIG_ARM64_PA_BITS;
> >  	}
> >  }
> > +
> > +/* Decouple AF from AFDBM. */
> 
> We could do with a better comment here or just remove it altogether. The
> aim of the patch was to decouple AF check from the AF+DBM but the
> comment here should describe what the function does. Maybe something
> like: "Check whether hardware update of the Access flag is supported".
> 

Okay, I will update it

--
Cheers,
Justin (Jia He)


> > +static inline bool cpu_has_hw_af(void)
> > +{
> > +	if (IS_ENABLED(CONFIG_ARM64_HW_AFDBM))
> > +		return read_cpuid(ID_AA64MMFR1_EL1) & 0xf;
> > +
> > +	return false;
> > +}
> 
> Other than the comment above,
> 
> Reviewed-by: Catalin Marinas <catalin.marinas@....com>