--- /dev/null
+/*
+ * 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))))
+
+/*
+ * On ARC700, EX insn is inherently atomic, so by default "vanilla" xchg() need
+ * not require any locking. However there's a quirk.
+ * ARC lacks native CMPXCHG, thus emulated (see above), using external locking -
+ * incidently it "reuses" the same atomic_ops_lock used by atomic APIs.
+ * Now, llist code uses cmpxchg() and xchg() on same data, so xchg() needs to
+ * abide by same serializing rules, thus ends up using atomic_ops_lock as well.
+ *
+ * This however is only relevant if SMP and/or ARC lacks LLSC
+ * if (UP or LLSC)
+ * xchg doesn't need serialization
+ * else <==> !(UP or LLSC) <==> (!UP and !LLSC) <==> (SMP and !LLSC)
+ * xchg needs serialization
+ */
+
+#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 relevent 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
Code Review / kvmfornfv.git / blobdiff