Implement FETCH-OP atomic primitives, these are very similar to the
existing OP-RETURN primitives we already have, except they return the
value of the atomic variable _before_ modification.
This is especially useful for irreversible operations -- such as
bitops (because it becomes impossible to reconstruct the state prior
to modification).
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
arch/m68k/include/asm/atomic.h | 53 +++++++++++++++++++++++++++++++++++++----
1 file changed, 49 insertions(+), 4 deletions(-)
--- a/arch/m68k/include/asm/atomic.h
+++ b/arch/m68k/include/asm/atomic.h
@@ -38,6 +38,13 @@ static inline void atomic_##op(int i, at
#ifdef CONFIG_RMW_INSNS
+/*
+ * Am I reading these CAS loops right in that %2 is the old value and the first
+ * iteration uses an uninitialized value?
+ *
+ * Would it not make sense to add: tmp = atomic_read(v); to avoid this?
+ */
+
#define ATOMIC_OP_RETURN(op, c_op, asm_op) \
static inline int atomic_##op##_return(int i, atomic_t *v) \
{ \
@@ -53,6 +60,21 @@ static inline int atomic_##op##_return(i
return t; \
}
+#define ATOMIC_FETCH_OP(op, c_op, asm_op) \
+static inline int atomic_fetch_##op(int i, atomic_t *v) \
+{ \
+ int t, tmp; \
+ \
+ __asm__ __volatile__( \
+ "1: movel %2,%1\n" \
+ " " #asm_op "l %3,%1\n" \
+ " casl %2,%1,%0\n" \
+ " jne 1b" \
+ : "+m" (*v), "=&d" (t), "=&d" (tmp) \
+ : "g" (i), "2" (atomic_read(v))); \
+ return tmp; \
+}
+
#else
#define ATOMIC_OP_RETURN(op, c_op, asm_op) \
@@ -68,20 +90,43 @@ static inline int atomic_##op##_return(i
return t; \
}
+#define ATOMIC_FETCH_OP(op, c_op, asm_op) \
+static inline int atomic_fetch_##op(int i, atomic_t * v) \
+{ \
+ unsigned long flags; \
+ int t; \
+ \
+ local_irq_save(flags); \
+ t = v->counter; \
+ v->counter c_op i; \
+ local_irq_restore(flags); \
+ \
+ return t; \
+}
+
#endif /* CONFIG_RMW_INSNS */
#define ATOMIC_OPS(op, c_op, asm_op) \
ATOMIC_OP(op, c_op, asm_op) \
- ATOMIC_OP_RETURN(op, c_op, asm_op)
+ ATOMIC_OP_RETURN(op, c_op, asm_op) \
+ ATOMIC_FETCH_OP(op, c_op, asm_op)
ATOMIC_OPS(add, +=, add)
ATOMIC_OPS(sub, -=, sub)
-ATOMIC_OP(and, &=, and)
-ATOMIC_OP(or, |=, or)
-ATOMIC_OP(xor, ^=, eor)
+#undef ATOMIC_OPS
+#define ATOMIC_OPS(op, c_op, asm_op) \
+ ATOMIC_OP(op, c_op, asm_op) \
+ ATOMIC_FETCH_OP(op, c_op, asm_op)
+
+#define atomic_fetch_or atomic_fetch_or
+
+ATOMIC_OPS(and, &=, and)
+ATOMIC_OPS(or, |=, or)
+ATOMIC_OPS(xor, ^=, eor)
#undef ATOMIC_OPS
+#undef ATOMIC_FETCH_OP
#undef ATOMIC_OP_RETURN
#undef ATOMIC_OP
--
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