[PATCH v5 3/3] xtensa: Emulate two-byte cmpxchg

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,
	brads@mainlining.org
Subject: [PATCH v5 3/3] xtensa: Emulate two-byte cmpxchg
Date: Mon,  5 Oct 2026 12:07:00 +0000	[thread overview]
Message-ID: <20261005120700.383058-4-brads@mainlining.org> (raw)
In-Reply-To: <20261005120700.383058-1-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 the
old and new values as unsigned long and narrows them itself, so
the call needs no extra casts.

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;
-- 
2.53.0

