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Subject: Re: [PATCH v5 4/7] powerpc/qspinlock: Add
 ARCH_USE_QUEUED_SPINLOCKS_XCHG32
To:     guoren@kernel.org
Cc:     linux-arch@vger.kernel.org, linux-xtensa@linux-xtensa.org,
        Guo Ren <guoren@linux.alibaba.com>,
        linux-kernel@vger.kernel.org, linux-csky@vger.kernel.org,
        openrisc@lists.librecores.org, Paul Mackerras <paulus@samba.org>,
        sparclinux@vger.kernel.org, linux-riscv@lists.infradead.org,
        linuxppc-dev@lists.ozlabs.org
References: <1616913028-83376-1-git-send-email-guoren@kernel.org>
 <1616913028-83376-5-git-send-email-guoren@kernel.org>
From:   Christophe Leroy <christophe.leroy@csgroup.eu>
Message-ID: <e27af5e0-a462-cb75-6311-1b5a6b4ee4f1@csgroup.eu>
Date:   Sun, 28 Mar 2021 13:14:28 +0200
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Le 28/03/2021 à 08:30, guoren@kernel.org a écrit :
> From: Guo Ren <guoren@linux.alibaba.com>
> 
> 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@gmail.com/

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@linux.alibaba.com>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: Paul Mackerras <paulus@samba.org>
> ---
>   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
>