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

Paul E. McKenney
2024-08-05T19:21:26Z

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. ]

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Vineet Gupta <vgupta@kernel.org>
Cc: Andi Shyti <andi.shyti@linux.intel.com>
Cc: Andrzej Hajda <andrzej.hajda@intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Palmer Dabbelt <palmer@rivosinc.com>
Cc: <linux-snps-arc@lists.infradead.org>
---
arch/arc/Kconfig | 1 +
arch/arc/include/asm/cmpxchg.h | 33 ++++++++++++++++++++++++---------
2 files changed, 25 insertions(+), 9 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..2102ce076f28b 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; \
@@ -65,16 +69,27 @@
__typeof__(*(ptr)) _prev_; \
unsigned long __flags; \
\
- BUILD_BUG_ON(sizeof(_p_) != 4); \
+ switch(sizeof((_p_))) { \
+ case 1: \
+ __flags = cmpxchg_emu_u8((volatile u8 *)_p_, (uintptr_t)_o_, (uintptr_t)_n_); \
+ _prev_ = (__typeof__(*(ptr)))__flags; \
+ break; \
+ break; \
+ case 4: \
+ /* \
+ * spin lock/unlock provide the needed smp_mb() \
+ * before/after \
+ */ \
+ atomic_ops_lock(__flags); \
+ _prev_ = *_p_; \
+ if (_prev_ == _o_) \
+ *_p_ = _n_; \
+ atomic_ops_unlock(__flags); \
+ break; \
+ default: \
+ BUILD_BUG(); \
+ } \
\
- /* \
- * spin lock/unlock provide the needed smp_mb() before/after \
- */ \
- atomic_ops_lock(__flags); \
- _prev_ = *_p_; \
- if (_prev_ == _o_) \
- *_p_ = _n_; \
- atomic_ops_unlock(__flags); \
_prev_; \
})

--
2.40.1