RE: [PATCH v4 1/3] arm64: cpufeature: introduce helper cpu_has_hw_af()

2019-09-18 Thread Justin He (Arm Technology China)
-ker...@lists.infradead.org; > linux-kernel@vger.kernel.org; linux...@kvack.org; Punit Agrawal > ; Anshuman Khandual > ; Jun Yao ; > Alex Van Brunt ; Robin Murphy > ; Thomas Gleixner ; > Andrew Morton ; Jérôme Glisse > ; Ralph Campbell ; > hejia...@gmail.com; Kaly Xin (Arm Tec

Re: [PATCH v4 1/3] arm64: cpufeature: introduce helper cpu_has_hw_af()

2019-09-18 Thread Catalin Marinas
On Wed, Sep 18, 2019 at 07:20:17AM -0700, Matthew Wilcox wrote: > On Wed, Sep 18, 2019 at 09:19:12PM +0800, Jia He wrote: > > +/* Decouple AF from AFDBM. */ > > +bool cpu_has_hw_af(void) > > +{ > > + return (read_cpuid(ID_AA64MMFR1_EL1) & 0xf); > > +} > > + > > Do you really want to call read_cp

Re: [PATCH v4 1/3] arm64: cpufeature: introduce helper cpu_has_hw_af()

2019-09-18 Thread Catalin Marinas
On Wed, Sep 18, 2019 at 03:20:41PM +0100, Suzuki K Poulose wrote: > On 18/09/2019 14:19, Jia He wrote: > > diff --git a/arch/arm64/include/asm/cpufeature.h > > b/arch/arm64/include/asm/cpufeature.h > > index c96ffa4722d3..206b6e3954cf 100644 > > --- a/arch/arm64/include/asm/cpufeature.h > > +++ b/

Re: [PATCH v4 1/3] arm64: cpufeature: introduce helper cpu_has_hw_af()

2019-09-18 Thread Suzuki K Poulose
Hi Jia, On 18/09/2019 14:19, 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: J

Re: [PATCH v4 1/3] arm64: cpufeature: introduce helper cpu_has_hw_af()

2019-09-18 Thread Matthew Wilcox
On Wed, Sep 18, 2019 at 09:19:12PM +0800, Jia He wrote: > +/* Decouple AF from AFDBM. */ > +bool cpu_has_hw_af(void) > +{ > + return (read_cpuid(ID_AA64MMFR1_EL1) & 0xf); > +} > + Do you really want to call read_cpuid() every time? I would have thought you'd want to use the static branch mech