[PATCH v2 5/5] xtensa: Emulate two-byte cmpxchg

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 v2 5/5] xtensa: Emulate two-byte cmpxchg
Date: Wed, 16 Sep 2026 20:02:15 +0000	[thread overview]
Message-ID: <20260916200215.21774-6-brads@mainlining.org> (raw)
In-Reply-To: <20260916200215.21774-1-brads@mainlining.org>

Xtensa has no two-byte atomic compare and swap, so the __cmpxchg()
switch lets case 2 fall through to __cmpxchg_called_with_bad_pointer(),
which is declared but never defined, so a two-byte cmpxchg() fails at
link time. Route case 2 through the new cmpxchg_emu_u16(), which takes
natural u16 arguments, so the unsigned long old and new narrow at the
function boundary.

Signed-off-by: Bradley Morgan <brads@mainlining.org>
---
 arch/xtensa/include/asm/cmpxchg.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/xtensa/include/asm/cmpxchg.h b/arch/xtensa/include/asm/cmpxchg.h
index b6db4838b175..8dea8e357fc0 100644
--- a/arch/xtensa/include/asm/cmpxchg.h
+++ b/arch/xtensa/include/asm/cmpxchg.h
@@ -76,6 +76,7 @@ __cmpxchg(volatile void *ptr, unsigned long old, unsigned long new, int size)
 {
 	switch (size) {
 	case 1:  return cmpxchg_emu_u8(ptr, old, new);
+	case 2:  return cmpxchg_emu_u16(ptr, old, new);
 	case 4:  return __cmpxchg_u32(ptr, old, new);
 	default: __cmpxchg_called_with_bad_pointer();
 		 return old;
-- 
2.47.3

