[PATCH cmpxchg 1/3] xtensa: Emulate one-byte cmpxchg

[Paul E. McKenney]

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

[ paulmck: Apply kernel test robot feedback. ]
[ paulmck: Drop two-byte support per Arnd Bergmann feedback. ]
[ Apply Geert Uytterhoeven feedback. ]

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Tested-by: Yujie Liu <yujie.liu@xxxxxxxxx>
Cc: Andi Shyti <andi.shyti@xxxxxxxxxxxxxxx>
Cc: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: "Peter Zijlstra (Intel)" <peterz@xxxxxxxxxxxxx>
---
 arch/xtensa/Kconfig               | 1 +
 arch/xtensa/include/asm/cmpxchg.h | 2 ++
 2 files changed, 3 insertions(+)

diff --git a/arch/xtensa/Kconfig b/arch/xtensa/Kconfig
index f200a4ec044e6..d3db28f2f8110 100644
--- a/arch/xtensa/Kconfig
+++ b/arch/xtensa/Kconfig
@@ -14,6 +14,7 @@ config XTENSA
 	select ARCH_HAS_DMA_SET_UNCACHED if MMU
 	select ARCH_HAS_STRNCPY_FROM_USER if !KASAN
 	select ARCH_HAS_STRNLEN_USER
+	select ARCH_NEED_CMPXCHG_1_EMU
 	select ARCH_USE_MEMTEST
 	select ARCH_USE_QUEUED_RWLOCKS
 	select ARCH_USE_QUEUED_SPINLOCKS
diff --git a/arch/xtensa/include/asm/cmpxchg.h b/arch/xtensa/include/asm/cmpxchg.h
index 675a11ea8de76..95e33a913962d 100644
--- a/arch/xtensa/include/asm/cmpxchg.h
+++ b/arch/xtensa/include/asm/cmpxchg.h
@@ -15,6 +15,7 @@
 
 #include <linux/bits.h>
 #include <linux/stringify.h>
+#include <linux/cmpxchg-emu.h>
 
 /*
  * cmpxchg
@@ -74,6 +75,7 @@ static __inline__ unsigned long
 __cmpxchg(volatile void *ptr, unsigned long old, unsigned long new, int size)
 {
 	switch (size) {
+	case 1:  return cmpxchg_emu_u8(ptr, old, new);
 	case 4:  return __cmpxchg_u32(ptr, old, new);
 	default: __cmpxchg_called_with_bad_pointer();
 		 return old;
-- 
2.40.1