linux-kernel - Re: [PATCH] atomic64: No need for CONFIG_ARCH_HAS_ATOMIC64_DEC_IF

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Message-ID: <20160908181905.GY10153@twins.programming.kicks-ass.net>
Date:   Thu, 8 Sep 2016 20:19:05 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Vineet Gupta <Vineet.Gupta1@...opsys.com>
Cc:     linux-kernel@...r.kernel.org,
        Alexey Brodkin <Alexey.Brodkin@...opsys.com>,
        Richard Henderson <rth@...ddle.net>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Matt Turner <mattst88@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        "James E.J. Bottomley" <jejb@...isc-linux.org>,
        Helge Deller <deller@....de>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        "David S. Miller" <davem@...emloft.net>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Zhaoxiu Zeng <zhaoxiu.zeng@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Matthew Wilcox <willy@...ux.intel.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Ming Lin <ming.l@....samsung.com>,
        Arnd Bergmann <arnd@...db.de>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Borislav Petkov <bp@...e.de>, Andi Kleen <ak@...ux.intel.com>,
        Boqun Feng <boqun.feng@...il.com>, linux-alpha@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-mips@...ux-mips.org,
        linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-snps-arc@...ts.infradead.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH] atomic64: No need for
 CONFIG_ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE

On Thu, Sep 08, 2016 at 09:28:18AM -0700, Vineet Gupta wrote:
> This came to light when implementing native 64-bit atomics for ARCv2.
> 
> The atomic64 self-test code uses CONFIG_ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE
> to check whether atomic64_dec_if_positive() is available.
> It seems it was needed when not every arch defined it.
> However as of current code the Kconfig option seems needless
> 
> - for CONFIG_GENERIC_ATOMIC64 it is auto-enabled in lib/Kconfig and a
>   generic definition of API is present lib/atomic64.c
> - arches with native 64-bit atomics select it in arch/*/Kconfig and
>   define the API in their headers
> 
> So I see no point in keeping the Kconfig option
> 
> Compile tested for 2 representatives:
>  - blackfin (CONFIG_GENERIC_ATOMIC64)
>  - x86 (!CONFIG_GENERIC_ATOMIC64)
> 
> Also logistics wise it seemed simpler to just do this in 1 patch vs.
> splitting per arch - but I can break it up if maintainer feel that
> is better to avoid conflicts.

Works for me; you want me to take this, or do you need it for you ARCv2
patches?