From: Catalin Marinas <catalin.marinas@arm.com>
To: "Justin He (Arm Technology China)" <Justin.He@arm.com>
Cc: Will Deacon <will@kernel.org>,
Mark Rutland <Mark.Rutland@arm.com>,
James Morse <James.Morse@arm.com>, Marc Zyngier <maz@kernel.org>,
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>,
Suzuki Poulose <Suzuki.Poulose@arm.com>,
Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>,
"x86@kernel.org" <x86@kernel.org>,
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>,
nd <nd@arm.com>
Subject: Re: [PATCH v11 1/4] arm64: cpufeature: introduce helper cpu_has_hw_af()
Date: Fri, 11 Oct 2019 11:38:58 +0100 [thread overview]
Message-ID: <20191011103857.GB54842@arrakis.emea.arm.com> (raw)
In-Reply-To: <DB7PR08MB3082E71F1FF5FE8462F88B8BF7970@DB7PR08MB3082.eurprd08.prod.outlook.com>
On Fri, Oct 11, 2019 at 01:16:36AM +0000, Justin He (Arm Technology China) wrote:
> From: Catalin Marinas <catalin.marinas@arm.com>
> > 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
next prev parent reply other threads:[~2019-10-11 10:39 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-09 8:42 [PATCH v11 0/4] fix double page fault in cow_user_page for pfn mapping Jia He
2019-10-09 8:42 ` [PATCH v11 1/4] arm64: cpufeature: introduce helper cpu_has_hw_af() Jia He
2019-10-10 16:43 ` Catalin Marinas
2019-10-11 1:16 ` Justin He (Arm Technology China)
2019-10-11 10:38 ` Catalin Marinas [this message]
2019-10-11 13:51 ` Justin He (Arm Technology China)
2019-10-09 8:42 ` [PATCH v11 2/4] arm64: mm: implement arch_faults_on_old_pte() on arm64 Jia He
2019-10-09 8:42 ` [PATCH v11 3/4] x86/mm: implement arch_faults_on_old_pte() stub on x86 Jia He
2019-10-09 8:42 ` [PATCH v11 4/4] mm: fix double page fault on arm64 if PTE_AF is cleared Jia He
2019-10-10 16:45 ` Catalin Marinas
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