Re: [PATCH v5 4/7] powerpc/qspinlock: Add ARCH_USE_QUEUED_SPINLOCKS_XCHG32

[Christophe Leroy]

Le 28/03/2021 à 08:30, guoren@xxxxxxxxxx a écrit :
> From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
>
> We don't have native hw xchg16 instruction, so let qspinlock
> generic code to deal with it.

We have lharx/sthcx pair on some versions of powerpc.

See https://patchwork.ozlabs.org/project/linuxppc-dev/patch/20201107032328.2454582-1-npiggin@xxxxxxxxx/

Christophe

> Using the full-word atomic xchg instructions implement xchg16 has
> the semantic risk for atomic operations.
>
> This patch cancels the dependency of on qspinlock generic code on
> architecture's xchg16.
>
> Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
> Cc: Paul Mackerras <paulus@xxxxxxxxx>
> ---
>   arch/powerpc/Kconfig | 1 +
>   1 file changed, 1 insertion(+)
>
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 386ae12d8523..69ec4ade6521 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -151,6 +151,7 @@ config PPC
>   	select ARCH_USE_CMPXCHG_LOCKREF		if PPC64
>   	select ARCH_USE_QUEUED_RWLOCKS		if PPC_QUEUED_SPINLOCKS
>   	select ARCH_USE_QUEUED_SPINLOCKS	if PPC_QUEUED_SPINLOCKS
> +	select ARCH_USE_QUEUED_SPINLOCKS_XCHG32	if PPC_QUEUED_SPINLOCKS
>   	select ARCH_WANT_IPC_PARSE_VERSION
>   	select ARCH_WANT_IRQS_OFF_ACTIVATE_MM
>   	select ARCH_WANT_LD_ORPHAN_WARN