Re: [PATCH v10 1/2] arch/*: Add CONFIG_ARCH_HAVE_CMPXCHG64

[Palmer Dabbelt]

On Tue, 15 May 2018 15:51:20 PDT (-0700), bart.vanassche@xxxxxxx 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@xxxxxxx>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Will Deacon <will.deacon@xxxxxxx>
> Cc: Tony Luck <tony.luck@xxxxxxxxx>
> Cc: Fenghua Yu <fenghua.yu@xxxxxxxxx>
> Cc: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> Cc: "James E.J. Bottomley" <jejb@xxxxxxxxxxxxxxxx>
> Cc: Helge Deller <deller@xxxxxx>
> Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
> Cc: Paul Mackerras <paulus@xxxxxxxxx>
> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
> Cc: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
> Cc: David S. Miller <davem@xxxxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: H. Peter Anvin <hpa@xxxxxxxxx>
> Cc: Chris Zankel <chris@xxxxxxxxxx>
> Cc: Max Filippov <jcmvbkbc@xxxxxxxxx>
> Cc: Arnd Bergmann <arnd@xxxxxxxx>
> Cc: Jonathan Corbet <corbet@xxxxxxx>
> ---
>  .../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...