From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH v2 3/5] locking/arch: Wire up local_try_cmpxchg
Date: Wed, 12 Apr 2023 13:32:31 +0200
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To: Uros Bizjak <ubizjak@gmail.com>
Cc: x86@kernel.org, Dave Hansen <dave.hansen@linux.intel.com>, Jiaxun Yang <jiaxun.yang@flygoat.com>, linux-kernel@vger.kernel.org, "H. Peter Anvin" <hpa@zytor.com>, WANG Xuerui <kernel@xen0n.name>, linux-arch@vger.kernel.org, Jun Yi <yijun@loongson.cn>, Huacai Chen <chenhuacai@kernel.org>, Ingo Molnar <mingo@redhat.com>, Matt Turner <mattst88@gmail.com>, Richard Henderson <richard.henderson@linaro.org>, Nicholas Piggin <npiggin@gmail.com>, Ivan Kokshaysky <ink@jurassic.park.msu.ru>, loongarch@lists.linux.dev, Thomas Gleixner <tglx@linutronix.de>, Thomas Bogendoerfer <tsbogend@alpha.franken.de>, linux-mips@vger.kernel.org, linux-perf-users@vger.kernel.org, linux-alpha@vger.kernel.org, Borislav Petkov <bp@alien8.de>, linuxppc-dev@lists.ozlabs.org

On Wed, Apr 05, 2023 at 04:17:08PM +0200, Uros Bizjak wrote:
> diff --git a/arch/powerpc/include/asm/local.h b/arch/powerpc/include/asm/local.h
> index bc4bd19b7fc2..45492fb5bf22 100644
> --- a/arch/powerpc/include/asm/local.h
> +++ b/arch/powerpc/include/asm/local.h
> @@ -90,6 +90,17 @@ static __inline__ long local_cmpxchg(local_t *l, long o, long n)
>  	return t;
>  }
>  
> +static __inline__ bool local_try_cmpxchg(local_t *l, long *po, long n)
> +{
> +	long o = *po, r;
> +
> +	r = local_cmpxchg(l, o, n);
> +	if (unlikely(r != o))
> +		*po = r;
> +
> +	return likely(r == o);
> +}
> +

Why is the ppc one different from the rest? Why can't it use the
try_cmpxchg_local() fallback and needs to have it open-coded?