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/*
* Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#ifndef __ASM_ARC_CMPXCHG_H
#define __ASM_ARC_CMPXCHG_H
#include <linux/types.h>
#include <asm/barrier.h>
#include <asm/smp.h>
#ifdef CONFIG_ARC_HAS_LLSC
static inline unsigned long
__cmpxchg(volatile void *ptr, unsigned long expected, unsigned long new)
{
unsigned long prev;
/*
* Explicit full memory barrier needed before/after as
* LLOCK/SCOND thmeselves don't provide any such semantics
*/
smp_mb();
__asm__ __volatile__(
"1: llock %0, [%1] \n"
" brne %0, %2, 2f \n"
" scond %3, [%1] \n"
" bnz 1b \n"
"2: \n"
: "=&r"(prev) /* Early clobber, to prevent reg reuse */
: "r"(ptr), /* Not "m": llock only supports reg direct addr mode */
"ir"(expected),
"r"(new) /* can't be "ir". scond can't take LIMM for "b" */
: "cc", "memory"); /* so that gcc knows memory is being written here */
smp_mb();
return prev;
}
#else
static inline unsigned long
__cmpxchg(volatile void *ptr, unsigned long expected, unsigned long new)
{
unsigned long flags;
int prev;
volatile unsigned long *p = ptr;
/*
* spin lock/unlock provide the needed smp_mb() before/after
*/
atomic_ops_lock(flags);
prev = *p;
if (prev == expected)
*p = new;
atomic_ops_unlock(flags);
return prev;
}
#endif /* CONFIG_ARC_HAS_LLSC */
#define cmpxchg(ptr, o, n) ((typeof(*(ptr)))__cmpxchg((ptr), \
(unsigned long)(o), (unsigned long)(n)))
/*
* Since not supported natively, ARC cmpxchg() uses atomic_ops_lock (UP/SMP)
* just to gaurantee semantics.
* atomic_cmpxchg() needs to use the same locks as it's other atomic siblings
* which also happens to be atomic_ops_lock.
*
* Thus despite semantically being different, implementation of atomic_cmpxchg()
* is same as cmpxchg().
*/
#define atomic_cmpxchg(v, o, n) ((int)cmpxchg(&((v)->counter), (o), (n)))
/*
* xchg (reg with memory) based on "Native atomic" EX insn
*/
static inline unsigned long __xchg(unsigned long val, volatile void *ptr,
int size)
{
extern unsigned long __xchg_bad_pointer(void);
switch (size) {
case 4:
smp_mb();
__asm__ __volatile__(
" ex %0, [%1] \n"
: "+r"(val)
: "r"(ptr)
: "memory");
smp_mb();
return val;
}
return __xchg_bad_pointer();
}
#define _xchg(ptr, with) ((typeof(*(ptr)))__xchg((unsigned long)(with), (ptr), \
sizeof(*(ptr))))
/*
* xchg() maps directly to ARC EX instruction which guarantees atomicity.
* However in !LLSC config, it also needs to be use @atomic_ops_lock spinlock
* due to a subtle reason:
* - For !LLSC, cmpxchg() needs to use that lock (see above) and there is lot
* of kernel code which calls xchg()/cmpxchg() on same data (see llist.h)
* Hence xchg() needs to follow same locking rules.
*
* Technically the lock is also needed for UP (boils down to irq save/restore)
* but we can cheat a bit since cmpxchg() atomic_ops_lock() would cause irqs to
* be disabled thus can't possibly be interrpted/preempted/clobbered by xchg()
* Other way around, xchg is one instruction anyways, so can't be interrupted
* as such
*/
#if !defined(CONFIG_ARC_HAS_LLSC) && defined(CONFIG_SMP)
#define xchg(ptr, with) \
({ \
unsigned long flags; \
typeof(*(ptr)) old_val; \
\
atomic_ops_lock(flags); \
old_val = _xchg(ptr, with); \
atomic_ops_unlock(flags); \
old_val; \
})
#else
#define xchg(ptr, with) _xchg(ptr, with)
#endif
/*
* "atomic" variant of xchg()
* REQ: It needs to follow the same serialization rules as other atomic_xxx()
* Since xchg() doesn't always do that, it would seem that following defintion
* is incorrect. But here's the rationale:
* SMP : Even xchg() takes the atomic_ops_lock, so OK.
* LLSC: atomic_ops_lock are not relevant at all (even if SMP, since LLSC
* is natively "SMP safe", no serialization required).
* UP : other atomics disable IRQ, so no way a difft ctxt atomic_xchg()
* could clobber them. atomic_xchg() itself would be 1 insn, so it
* can't be clobbered by others. Thus no serialization required when
* atomic_xchg is involved.
*/
#define atomic_xchg(v, new) (xchg(&((v)->counter), new))
#endif
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