sh: Emulate one-byte cmpxchg

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

[ paulmck: Drop two-byte support per Arnd Bergmann feedback. ]
[ paulmck: Apply feedback from Naresh Kamboju. ]
[ Apply Geert Uytterhoeven feedback. ]

Signed-off-by: Paul E. McKenney <[email protected]>
Cc: Andi Shyti <[email protected]>
Cc: Palmer Dabbelt <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: <[email protected]>
Acked-by: John Paul Adrian Glaubitz <[email protected]>

Author: paulmckrcu

arch/sh/Kconfig

@@ -14,6 +14,7 @@ config SUPERH
 	select ARCH_HIBERNATION_POSSIBLE if MMU
 	select ARCH_MIGHT_HAVE_PC_PARPORT
 	select ARCH_WANT_IPC_PARSE_VERSION
+	select ARCH_NEED_CMPXCHG_1_EMU
 	select CPU_NO_EFFICIENT_FFS
 	select DMA_DECLARE_COHERENT
 	select GENERIC_ATOMIC64

arch/sh/include/asm/cmpxchg.h

@@ -9,6 +9,7 @@
 
 #include <linux/compiler.h>
 #include <linux/types.h>
+#include <linux/cmpxchg-emu.h>
 
 #if defined(CONFIG_GUSA_RB)
 #include <asm/cmpxchg-grb.h>
@@ -56,6 +57,8 @@ 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);
 	}