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From: Bradley Morgan <brads@mainlining.org>
To: akpm@linux-foundation.org, vgupta@kernel.org, guoren@kernel.org,
	chris@zankel.net, jcmvbkbc@gmail.com
Cc: arnd@arndb.de, paulmck@kernel.org, david.laight.linux@gmail.com,
	glaubitz@physik.fu-berlin.de, ysato@users.sourceforge.jp,
	dalias@libc.org, linux-snps-arc@lists.infradead.org,
	linux-csky@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5 1/3] ARC: Emulate two-byte cmpxchg
Date: Mon, 05 Oct 2026 13:08:05 +0100	[thread overview]
Message-ID: <DFEBDABC-BF95-4AF7-863C-7C25F1443B28@mainlining.org> (raw)
In-Reply-To: <20261005120556.383004-2-brads@mainlining.org>

On 5 October 2026 13:05:54 BST, Bradley Morgan <brads@mainlining.org>
wrote:
>ARC has no two-byte atomic compare and swap, so the
>arch_cmpxchg_relaxed() macro switch lets case 2 fall through to
>BUILD_BUG() via default, and a two-byte cmpxchg() fails the build.
>
>Route case 2 through the new cmpxchg_emu_u16(), which narrows the
>old and new values itself, so the dispatch keeps the (uintptr_t)
>casts the case 1 path already uses.
>
>The sizeof(*(_p_)) fix that v4 folded in here landed separately
>through Vineet's f050c3e61d2a, so this patch is now only the
>case 2 wiring.
>
>Signed-off-by: Bradley Morgan <brads@mainlining.org>
>---
> arch/arc/include/asm/cmpxchg.h | 3 +++
> 1 file changed, 3 insertions(+)
>
>diff --git a/arch/arc/include/asm/cmpxchg.h b/arch/arc/include/asm/cmpxchg.h
>index 66b3743c9400..b30b20933f32 100644
>--- a/arch/arc/include/asm/cmpxchg.h
>+++ b/arch/arc/include/asm/cmpxchg.h
>@@ -50,6 +50,9 @@
> 	case 1:								\
> 		_prev_ = (__typeof__(*(ptr)))cmpxchg_emu_u8((volatile u8 *__force)_p_, (uintptr_t)_o_, (uintptr_t)_n_);	\
> 		break;							\
>+	case 2:								\
>+		_prev_ = (__typeof__(*(ptr)))cmpxchg_emu_u16((volatile u16 *__force)_p_, (unsigned long)_o_, (unsigned long)_n_);	\
>+		break;							\
> 	case 4:								\
> 		_prev_ = __cmpxchg(_p_, _o_, _n_);			\
> 		break;							\
>
Sorry, resent email, internet went out ;(
--- Thanks!
"I'm not a very positive person" - Linus torvalds

WARNING: multiple messages have this Message-ID (diff)
From: Bradley Morgan <brads@mainlining.org>
To: akpm@linux-foundation.org, vgupta@kernel.org, guoren@kernel.org,
	chris@zankel.net, jcmvbkbc@gmail.com
Cc: arnd@arndb.de, paulmck@kernel.org, david.laight.linux@gmail.com,
	glaubitz@physik.fu-berlin.de, ysato@users.sourceforge.jp,
	dalias@libc.org, linux-snps-arc@lists.infradead.org,
	linux-csky@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5 1/3] ARC: Emulate two-byte cmpxchg
Date: Mon, 05 Oct 2026 13:08:05 +0100	[thread overview]
Message-ID: <DFEBDABC-BF95-4AF7-863C-7C25F1443B28@mainlining.org> (raw)
In-Reply-To: <20261005120556.383004-2-brads@mainlining.org>

On 5 October 2026 13:05:54 BST, Bradley Morgan <brads@mainlining.org>
wrote:
>ARC has no two-byte atomic compare and swap, so the
>arch_cmpxchg_relaxed() macro switch lets case 2 fall through to
>BUILD_BUG() via default, and a two-byte cmpxchg() fails the build.
>
>Route case 2 through the new cmpxchg_emu_u16(), which narrows the
>old and new values itself, so the dispatch keeps the (uintptr_t)
>casts the case 1 path already uses.
>
>The sizeof(*(_p_)) fix that v4 folded in here landed separately
>through Vineet's f050c3e61d2a, so this patch is now only the
>case 2 wiring.
>
>Signed-off-by: Bradley Morgan <brads@mainlining.org>
>---
> arch/arc/include/asm/cmpxchg.h | 3 +++
> 1 file changed, 3 insertions(+)
>
>diff --git a/arch/arc/include/asm/cmpxchg.h b/arch/arc/include/asm/cmpxchg.h
>index 66b3743c9400..b30b20933f32 100644
>--- a/arch/arc/include/asm/cmpxchg.h
>+++ b/arch/arc/include/asm/cmpxchg.h
>@@ -50,6 +50,9 @@
> 	case 1:								\
> 		_prev_ = (__typeof__(*(ptr)))cmpxchg_emu_u8((volatile u8 *__force)_p_, (uintptr_t)_o_, (uintptr_t)_n_);	\
> 		break;							\
>+	case 2:								\
>+		_prev_ = (__typeof__(*(ptr)))cmpxchg_emu_u16((volatile u16 *__force)_p_, (unsigned long)_o_, (unsigned long)_n_);	\
>+		break;							\
> 	case 4:								\
> 		_prev_ = __cmpxchg(_p_, _o_, _n_);			\
> 		break;							\
>
Sorry, resent email, internet went out ;(
--- Thanks!
"I'm not a very positive person" - Linus torvalds

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  reply	other threads:[~2026-10-05 12:10 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-10-05 12:05 [PATCH v5 0/3] Add two-byte cmpxchg emulation and wire it into the architectures Bradley Morgan
2026-10-05 12:05 ` Bradley Morgan
2026-10-05 12:05 ` [PATCH v5 1/3] ARC: Emulate two-byte cmpxchg Bradley Morgan
2026-10-05 12:05   ` Bradley Morgan
2026-10-05 12:08   ` Bradley Morgan [this message]
2026-10-05 12:08     ` Bradley Morgan
2026-10-05 12:05 ` [PATCH v5 2/3] csky: " Bradley Morgan
2026-10-05 12:05   ` Bradley Morgan
2026-10-05 12:05 ` [PATCH v5 3/3] xtensa: " Bradley Morgan
2026-10-05 12:05   ` Bradley Morgan
  -- strict thread matches above, loose matches on Subject: below --
2026-10-05 12:06 [PATCH v5 0/3] Add two-byte cmpxchg emulation and wire it into the architectures Bradley Morgan
2026-10-05 12:06 ` [PATCH v5 1/3] ARC: Emulate two-byte cmpxchg Bradley Morgan
2026-10-05 12:06   ` Bradley Morgan
2026-10-06  9:55   ` kernel test robot
2026-10-06  9:55     ` kernel test robot

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