RE: [PATCH v8 1/3] arm64: cpufeature: introduce helper cpu_has_hw_af()

[Justin He (Arm Technology China)]

Hi Catalin

> -----Original Message-----
> From: Catalin Marinas <catalin.marinas@xxxxxxx>
> Sent: 2019å9æ24æ 0:07
> To: Justin He (Arm Technology China) <Justin.He@xxxxxxx>
> Cc: Will Deacon <will@xxxxxxxxxx>; Mark Rutland
> <Mark.Rutland@xxxxxxx>; James Morse <James.Morse@xxxxxxx>; Marc
> Zyngier <maz@xxxxxxxxxx>; Matthew Wilcox <willy@xxxxxxxxxxxxx>; Kirill A.
> Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>; linux-arm-
> kernel@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux-
> mm@xxxxxxxxx; Suzuki Poulose <Suzuki.Poulose@xxxxxxx>; Punit
> Agrawal <punitagrawal@xxxxxxxxx>; Anshuman Khandual
> <Anshuman.Khandual@xxxxxxx>; Alex Van Brunt
> <avanbrunt@xxxxxxxxxx>; Robin Murphy <Robin.Murphy@xxxxxxx>;
> Thomas Gleixner <tglx@xxxxxxxxxxxxx>; Andrew Morton <akpm@linux-
> foundation.org>; JÃrÃme Glisse <jglisse@xxxxxxxxxx>; Ralph Campbell
> <rcampbell@xxxxxxxxxx>; hejianet@xxxxxxxxx; Kaly Xin (Arm Technology
> China) <Kaly.Xin@xxxxxxx>; nd <nd@xxxxxxx>
> 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@xxxxxxxxx>
> > Suggested-by: Suzuki Poulose <Suzuki.Poulose@xxxxxxx>
> > Signed-off-by: Jia He <justin.he@xxxxxxx>
> > ---
> >  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@xxxxxxx>