[PATCH v3 cmpxchg 4/4] ARM: Emulate one-byte cmpxchg

Paul E. McKenney
2024-06-04T17:04:41Z

Use the new cmpxchg_emu_u8() to emulate one-byte cmpxchg() on ARM systems
with ARCH < ARMv6K.

[ paulmck: Apply Arnd Bergmann and Nathan Chancellor feedback. ]

Reported-by: Mark Brown <broonie@kernel.org>
Closes: https://lore.kernel.org/all/54798f68-48f7-4c65-9cba-47c0bf175143@sirena.org.uk/
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Closes: https://lore.kernel.org/all/CA+G9fYuZ+pf6p8AXMZWtdFtX-gbG8HMaBKp=XbxcdzA_QeLkxQ@mail.gmail.com/
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Cc: "Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Andrew Davis <afd@ti.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Eric DeVolder <eric.devolder@oracle.com>
Cc: Rob Herring <robh@kernel.org>
Cc: <linux-arm-kernel@lists.infradead.org>
---
arch/arm/Kconfig | 1 +
arch/arm/include/asm/cmpxchg.h | 7 ++++++-
2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index ee5115252aac4..a867a7d967aa5 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -34,6 +34,7 @@ config ARM
select ARCH_MIGHT_HAVE_PC_PARPORT
select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX
select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT if CPU_V7
+ select ARCH_NEED_CMPXCHG_1_EMU if CPU_V6
select ARCH_SUPPORTS_ATOMIC_RMW
select ARCH_SUPPORTS_CFI_CLANG
select ARCH_SUPPORTS_HUGETLBFS if ARM_LPAE
diff --git a/arch/arm/include/asm/cmpxchg.h b/arch/arm/include/asm/cmpxchg.h
index 44667bdb4707a..a428e06fe94ee 100644
--- a/arch/arm/include/asm/cmpxchg.h
+++ b/arch/arm/include/asm/cmpxchg.h
@@ -5,6 +5,7 @@
#include <linux/irqflags.h>
#include <linux/prefetch.h>
#include <asm/barrier.h>
+#include <linux/cmpxchg-emu.h>

#if defined(CONFIG_CPU_SA1100) || defined(CONFIG_CPU_SA110)
/*
@@ -162,7 +163,11 @@ static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
prefetchw((const void *)ptr);

switch (size) {
-#ifndef CONFIG_CPU_V6 /* min ARCH >= ARMv6K */
+#ifdef CONFIG_CPU_V6 /* min ARCH < ARMv6K */
+ case 1:
+ oldval = cmpxchg_emu_u8((volatile u8 *)ptr, old, new);
+ break;
+#else /* min ARCH >= ARMv6K */
case 1:
do {
asm volatile("@ __cmpxchg1\n"
--
2.40.1