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From: Bradley Morgan <brads@mainlining.org>
To: Andrew Morton <akpm@linux-foundation.org>,
	Vineet Gupta <vgupta@kernel.org>, Guo Ren <guoren@kernel.org>,
	Yoshinori Sato <ysato@users.sourceforge.jp>,
	Rich Felker <dalias@libc.org>, Chris Zankel <chris@zankel.net>,
	Max Filippov <jcmvbkbc@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>,
	"Paul E . McKenney" <paulmck@kernel.org>,
	David Laight <david.laight.linux@gmail.com>,
	John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>,
	linux-snps-arc@lists.infradead.org, linux-csky@vger.kernel.org,
	linux-sh@vger.kernel.org, linux-kernel@vger.kernel.org,
	Bradley Morgan <brads@mainlining.org>
Subject: [PATCH v3 2/5] ARC: Emulate two-byte cmpxchg
Date: Thu, 17 Sep 2026 16:38:27 +0000	[thread overview]
Message-ID: <20260917163830.3748-3-brads@mainlining.org> (raw)
In-Reply-To: <20260917163830.3748-1-brads@mainlining.org>

ARC has no two-byte atomic compare and swap, so the __cmpxchg() macro
switch lets case 2 fall through to BUILD_BUG() via default. Route case
2 through the new cmpxchg_emu_u16(), which takes the old and new
values as unsigned long and narrows them itself, so the (uintptr_t)
casts on _o_ and _n_ are no longer needed and the case 2 call passes
them straight.

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 76f43db0890f..9b48b8fe0db2 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_, (uintptr_t)_o_, (uintptr_t)_n_);	\
+		break;							\
 	case 4:								\
 		_prev_ = __cmpxchg(_p_, _o_, _n_);			\
 		break;							\
-- 
2.47.3


WARNING: multiple messages have this Message-ID (diff)
From: Bradley Morgan <brads@mainlining.org>
To: Andrew Morton <akpm@linux-foundation.org>,
	Vineet Gupta <vgupta@kernel.org>, Guo Ren <guoren@kernel.org>,
	Yoshinori Sato <ysato@users.sourceforge.jp>,
	Rich Felker <dalias@libc.org>, Chris Zankel <chris@zankel.net>,
	Max Filippov <jcmvbkbc@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>,
	"Paul E . McKenney" <paulmck@kernel.org>,
	David Laight <david.laight.linux@gmail.com>,
	John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>,
	linux-snps-arc@lists.infradead.org, linux-csky@vger.kernel.org,
	linux-sh@vger.kernel.org, linux-kernel@vger.kernel.org,
	Bradley Morgan <brads@mainlining.org>
Subject: [PATCH v3 2/5] ARC: Emulate two-byte cmpxchg
Date: Thu, 17 Sep 2026 16:38:27 +0000	[thread overview]
Message-ID: <20260917163830.3748-3-brads@mainlining.org> (raw)
In-Reply-To: <20260917163830.3748-1-brads@mainlining.org>

ARC has no two-byte atomic compare and swap, so the __cmpxchg() macro
switch lets case 2 fall through to BUILD_BUG() via default. Route case
2 through the new cmpxchg_emu_u16(), which takes the old and new
values as unsigned long and narrows them itself, so the (uintptr_t)
casts on _o_ and _n_ are no longer needed and the case 2 call passes
them straight.

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 76f43db0890f..9b48b8fe0db2 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_, (uintptr_t)_o_, (uintptr_t)_n_);	\
+		break;							\
 	case 4:								\
 		_prev_ = __cmpxchg(_p_, _o_, _n_);			\
 		break;							\
-- 
2.47.3

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  parent reply	other threads:[~2026-09-17 16:40 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-09-17 16:38 [PATCH v3 0/5] Add two-byte cmpxchg emulation and wire it into the architectures Bradley Morgan
2026-09-17 16:38 ` Bradley Morgan
2026-09-17 16:38 ` [PATCH v3 1/5] lib: Add two-byte cmpxchg emulation function Bradley Morgan
2026-09-17 16:38   ` Bradley Morgan
2026-09-18  8:59   ` David Laight
2026-09-18  8:59     ` David Laight
2026-09-17 16:38 ` Bradley Morgan [this message]
2026-09-17 16:38   ` [PATCH v3 2/5] ARC: Emulate two-byte cmpxchg Bradley Morgan
2026-09-17 16:38 ` [PATCH v3 3/5] csky: " Bradley Morgan
2026-09-17 16:38   ` Bradley Morgan
2026-09-17 16:38 ` [PATCH v3 4/5] sh: " Bradley Morgan
2026-09-17 16:38   ` Bradley Morgan
2026-09-17 16:38 ` [PATCH v3 5/5] xtensa: " Bradley Morgan
2026-09-17 16:38   ` Bradley Morgan
2026-09-17 16:42   ` Bradley Morgan
2026-09-17 16:42     ` Bradley Morgan
2026-09-18  9:10 ` [PATCH v3 0/5] Add two-byte cmpxchg emulation and wire it into the architectures David Laight
2026-09-18  9:10   ` David Laight

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