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SubjectRe: [PATCH V2 11/19] csky: Atomic operations
On Mon, Jul 02, 2018 at 01:30:14AM +0800, Guo Ren wrote:

> +#include <asm/barrier.h>
> +
> +#define __xchg(new, ptr, size) \
> +({ \
> + __typeof__(ptr) __ptr = (ptr); \
> + __typeof__(new) __new = (new); \
> + __typeof__(*(ptr)) __ret; \
> + unsigned long tmp; \
> + switch (size) { \
> + case 4: \
> + asm volatile ( \
> + "1: ldex.w %0, (%3) \n" \
> + " mov %1, %2 \n" \
> + " stex.w %1, (%3) \n" \
> + " bez %1, 1b \n" \
> + : "=&r" (__ret), "=&r" (tmp) \
> + : "r" (__new), "r"(__ptr) \
> + : "memory"); \
> + smp_mb(); \
> + break; \
> + default: \
> + BUILD_BUG(); \
> + } \
> + __ret; \
> +})
> +
> +#define xchg(ptr, x) (__xchg((x), (ptr), sizeof(*(ptr))))
> +
> +#define __cmpxchg(ptr, old, new, size) \
> +({ \
> + __typeof__(ptr) __ptr = (ptr); \
> + __typeof__(new) __new = (new); \
> + __typeof__(new) __tmp; \
> + __typeof__(old) __old = (old); \
> + __typeof__(*(ptr)) __ret; \
> + switch (size) { \
> + case 4: \
> + asm volatile ( \
> + "1: ldex.w %0, (%3) \n" \
> + " cmpne %0, %4 \n" \
> + " bt 2f \n" \
> + " mov %1, %2 \n" \
> + " stex.w %1, (%3) \n" \
> + " bez %1, 1b \n" \
> + "2: \n" \
> + : "=&r" (__ret), "=&r" (__tmp) \
> + : "r" (__new), "r"(__ptr), "r"(__old) \
> + : "memory"); \
> + smp_mb(); \
> + break; \
> + default: \
> + BUILD_BUG(); \
> + } \
> + __ret; \
> +})
> +
> +#define cmpxchg(ptr, o, n) \
> + (__cmpxchg((ptr), (o), (n), sizeof(*(ptr))))

What's the memory ordering rules for your LDEX/STEX ?

The mandated semantics for xchg() / cmpxchg() is an effective smp_mb()
before _and_ after.

The above implementation suggests LDEX implies a SYNC.IS, is this
correct?

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