RE: [PATCH v10 1/3] arm64: cpufeature: introduce helper cpu_has_hw_af()

From: "Justin He (Arm Technology China)" <Justin.He@arm.com>
To: Marc Zyngier <maz@kernel.org>, Will Deacon <will@kernel.org>
Cc: Catalin Marinas <Catalin.Marinas@arm.com>,
	Mark Rutland <Mark.Rutland@arm.com>,
	James Morse <James.Morse@arm.com>,
	Matthew Wilcox <willy@infradead.org>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	Punit Agrawal <punitagrawal@gmail.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	"hejianet@gmail.com" <hejianet@gmail.com>,
	"Kaly Xin (Arm Technology China)" <Kaly.Xin@arm.com>
Subject: RE: [PATCH v10 1/3] arm64: cpufeature: introduce helper cpu_has_hw_af()
Date: Tue, 8 Oct 2019 01:12:05 +0000	[thread overview]
Message-ID: <DB7PR08MB30824EFD975EE9BACAC7FD52F79A0@DB7PR08MB3082.eurprd08.prod.outlook.com> (raw)
In-Reply-To: <20191001141848.762296bd@why>

Hi Will and Marc
Sorry for the late response, just came back from a vacation.

> -----Original Message-----
> From: Marc Zyngier <maz@kernel.org>
> Sent: 2019年10月1日 21:19
> To: Will Deacon <will@kernel.org>
> Cc: Justin He (Arm Technology China) <Justin.He@arm.com>; Catalin
> Marinas <Catalin.Marinas@arm.com>; Mark Rutland
> <Mark.Rutland@arm.com>; James Morse <James.Morse@arm.com>;
> Matthew Wilcox <willy@infradead.org>; Kirill A. Shutemov
> <kirill.shutemov@linux.intel.com>; linux-arm-kernel@lists.infradead.org;
> linux-kernel@vger.kernel.org; linux-mm@kvack.org; Punit Agrawal
> <punitagrawal@gmail.com>; Thomas Gleixner <tglx@linutronix.de>;
> Andrew Morton <akpm@linux-foundation.org>; hejianet@gmail.com; Kaly
> Xin (Arm Technology China) <Kaly.Xin@arm.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@kernel.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@arm.com>
> > > Suggested-by: Suzuki Poulose <Suzuki.Poulose@arm.com>
> > > Reviewed-by: Catalin Marinas <catalin.marinas@arm.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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