linux-kernel - Re: [PATCH v10 1/2] arch/*: Add CONFIG_ARCH_HAVE

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Message-ID: <mhng-26ddbf89-8276-47a4-9235-e900f91fa575@palmer-si-x1c4>
Date:   Fri, 18 May 2018 13:33:13 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...ive.com>
To:     bart.vanassche@....com
CC:     axboe@...nel.dk, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, Christoph Hellwig <hch@....de>,
        bart.vanassche@....com, catalin.marinas@....com,
        Will Deacon <will.deacon@....com>, tony.luck@...el.com,
        fenghua.yu@...el.com, geert@...ux-m68k.org, jejb@...isc-linux.org,
        deller@....de, benh@...nel.crashing.org, paulus@...ba.org,
        mpe@...erman.id.au, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, davem@...emloft.net, tglx@...utronix.de,
        mingo@...hat.com, hpa@...or.com, chris@...kel.net,
        jcmvbkbc@...il.com, Arnd Bergmann <arnd@...db.de>, corbet@....net
Subject:     Re: [PATCH v10 1/2] arch/*: Add CONFIG_ARCH_HAVE_CMPXCHG64

On Tue, 15 May 2018 15:51:20 PDT (-0700), bart.vanassche@....com wrote:
> The next patch in this series introduces a call to cmpxchg64()
> in the block layer core for those architectures on which this
> functionality is available. Make it possible to test whether
> cmpxchg64() is available by introducing CONFIG_ARCH_HAVE_CMPXCHG64.
>
> Signed-off-by: Bart Van Assche <bart.vanassche@....com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will.deacon@....com>
> Cc: Tony Luck <tony.luck@...el.com>
> Cc: Fenghua Yu <fenghua.yu@...el.com>
> Cc: Geert Uytterhoeven <geert@...ux-m68k.org>
> Cc: "James E.J. Bottomley" <jejb@...isc-linux.org>
> Cc: Helge Deller <deller@....de>
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: Martin Schwidefsky <schwidefsky@...ibm.com>
> Cc: Heiko Carstens <heiko.carstens@...ibm.com>
> Cc: David S. Miller <davem@...emloft.net>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: H. Peter Anvin <hpa@...or.com>
> Cc: Chris Zankel <chris@...kel.net>
> Cc: Max Filippov <jcmvbkbc@...il.com>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Jonathan Corbet <corbet@....net>
> ---
>  .../features/locking/cmpxchg64/arch-support.txt    | 33 ++++++++++++++++++++++
>  arch/Kconfig                                       |  3 ++
>  arch/alpha/Kconfig                                 |  1 +
>  arch/arm/Kconfig                                   |  1 +
>  arch/arm64/Kconfig                                 |  1 +
>  arch/ia64/Kconfig                                  |  1 +
>  arch/m68k/Kconfig                                  |  1 +
>  arch/mips/Kconfig                                  |  1 +
>  arch/parisc/Kconfig                                |  1 +
>  arch/powerpc/Kconfig                               |  1 +
>  arch/riscv/Kconfig                                 |  1 +
>  arch/s390/Kconfig                                  |  1 +
>  arch/sparc/Kconfig                                 |  1 +
>  arch/x86/Kconfig                                   |  1 +
>  arch/xtensa/Kconfig                                |  1 +
>  15 files changed, 49 insertions(+)
>  create mode 100644 Documentation/features/locking/cmpxchg64/arch-support.txt

[...]

> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -8,6 +8,7 @@ config RISCV
>  	select OF
>  	select OF_EARLY_FLATTREE
>  	select OF_IRQ
> +	select ARCH_HAVE_CMPXCHG64
>  	select ARCH_WANT_FRAME_POINTERS
>  	select CLONE_BACKWARDS
>  	select COMMON_CLK

If I understand correctly, we should only have ARCH_HAVE_CMPXCHG64 on 64-bit 
RISC-V systems so this should look something like

   select ARCH_HAVE_CMPXCHG64 if 64BIT

Of course, the RV32I port is broken right now so it's not a big deal, but we're 
working through making it less broken...