linux-kernel - [PATCH v2 cmpxchg 2/3] ARC: Emulate one-byte cmpxchg

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Message-Id: <20240821181011.2604152-2-paulmck@kernel.org>
Date: Wed, 21 Aug 2024 11:10:10 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	elver@...gle.com
Cc: akpm@...ux-foundation.org,
	tglx@...utronix.de,
	peterz@...radead.org,
	torvalds@...ux-foundation.org,
	arnd@...db.de,
	geert@...ux-m68k.org,
	kernel-team@...a.com,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Andi Shyti <andi.shyti@...ux.intel.com>,
	Andrzej Hajda <andrzej.hajda@...el.com>,
	Palmer Dabbelt <palmer@...osinc.com>,
	linux-snps-arc@...ts.infradead.org,
	Vineet Gupta <vgupta@...nel.org>
Subject: [PATCH v2 cmpxchg 2/3] ARC: Emulate one-byte cmpxchg

Use the new cmpxchg_emu_u8() to emulate one-byte cmpxchg() on arc.

[ paulmck: Drop two-byte support per Arnd Bergmann feedback. ]
[ paulmck: Apply feedback from Naresh Kamboju. ]
[ paulmck: Apply kernel test robot feedback. ]
[ paulmck: Apply feedback from Vineet Gupta. ]

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
Cc: Andi Shyti <andi.shyti@...ux.intel.com>
Cc: Andrzej Hajda <andrzej.hajda@...el.com>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Palmer Dabbelt <palmer@...osinc.com>
Cc: <linux-snps-arc@...ts.infradead.org>
Acked-by: Vineet Gupta <vgupta@...nel.org>
---
 arch/arc/Kconfig               | 1 +
 arch/arc/include/asm/cmpxchg.h | 6 ++++--
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
index fd0b0a0d4686a..163608fd49d18 100644
--- a/arch/arc/Kconfig
+++ b/arch/arc/Kconfig
@@ -13,6 +13,7 @@ config ARC
 	select ARCH_HAS_SETUP_DMA_OPS
 	select ARCH_HAS_SYNC_DMA_FOR_CPU
 	select ARCH_HAS_SYNC_DMA_FOR_DEVICE
+	select ARCH_NEED_CMPXCHG_1_EMU
 	select ARCH_SUPPORTS_ATOMIC_RMW if ARC_HAS_LLSC
 	select ARCH_32BIT_OFF_T
 	select BUILDTIME_TABLE_SORT
diff --git a/arch/arc/include/asm/cmpxchg.h b/arch/arc/include/asm/cmpxchg.h
index e138fde067dea..58045c8983404 100644
--- a/arch/arc/include/asm/cmpxchg.h
+++ b/arch/arc/include/asm/cmpxchg.h
@@ -8,6 +8,7 @@
 
 #include <linux/build_bug.h>
 #include <linux/types.h>
+#include <linux/cmpxchg-emu.h>
 
 #include <asm/barrier.h>
 #include <asm/smp.h>
@@ -46,6 +47,9 @@
 	__typeof__(*(ptr)) _prev_;					\
 									\
 	switch(sizeof((_p_))) {						\
+	case 1:								\
+		_prev_ = (__typeof__(*(ptr)))cmpxchg_emu_u8((volatile u8 *)_p_, (uintptr_t)_o_, (uintptr_t)_n_);	\
+		break;							\
 	case 4:								\
 		_prev_ = __cmpxchg(_p_, _o_, _n_);			\
 		break;							\
@@ -65,8 +69,6 @@
 	__typeof__(*(ptr)) _prev_;					\
 	unsigned long __flags;						\
 									\
-	BUILD_BUG_ON(sizeof(_p_) != 4);					\
-									\
 	/*								\
 	 * spin lock/unlock provide the needed smp_mb() before/after	\
 	 */								\
-- 
2.40.1