Hi Catanlin Thanks for the detailed explanation. Will send out v12 soon after testing
-- Cheers, Justin (Jia He) > -----Original Message----- > From: Catalin Marinas <[email protected]> > Sent: Friday, October 11, 2019 6:39 PM > To: Justin He (Arm Technology China) <[email protected]> > Cc: Will Deacon <[email protected]>; Mark Rutland > <[email protected]>; James Morse <[email protected]>; Marc > Zyngier <[email protected]>; Matthew Wilcox <[email protected]>; Kirill A. > Shutemov <[email protected]>; linux-arm- > [email protected]; [email protected]; linux- > [email protected]; Suzuki Poulose <[email protected]>; Borislav > Petkov <[email protected]>; H. Peter Anvin <[email protected]>; [email protected]; > Thomas Gleixner <[email protected]>; Andrew Morton <akpm@linux- > foundation.org>; [email protected]; Kaly Xin (Arm Technology China) > <[email protected]>; nd <[email protected]> > Subject: Re: [PATCH v11 1/4] arm64: cpufeature: introduce helper > cpu_has_hw_af() > > On Fri, Oct 11, 2019 at 01:16:36AM +0000, Justin He (Arm Technology China) > wrote: > > From: Catalin Marinas <[email protected]> > > > On Wed, Oct 09, 2019 at 04:42:43PM +0800, Jia He wrote: > > > > + u64 mmfr1 = read_cpuid(ID_AA64MMFR1_EL1); > > > > + > > > > + return !!cpuid_feature_extract_unsigned_field(mmfr1, > > > > + > > > ID_AA64MMFR1_HADBS_SHIFT); > > > > > > No need for !!, the return type is a bool already. > > > > But cpuid_feature_extract_unsigned_field has the return type "unsigned > int" [1] > > > > [1] > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch > /arm64/include/asm/cpufeature.h#n444 > > And the C language gives you the automatic conversion from unsigned int > to bool without the need for !!. The reason we use !! in some places is > for converting long to int (not bool) and losing the top 32-bit. See > commit 84fe6826c28f ("arm64: mm: Add double logical invert to pte > accessors") for an explanation. > > -- > Catalin
