lib: Provide generic atomic64_t implementation

Many processor architectures have no 64-bit atomic instructions, but
we need atomic64_t in order to support the perf_counter subsystem.

This adds an implementation of 64-bit atomic operations using hashed
spinlocks to provide atomicity.  For each atomic operation, the address
of the atomic64_t variable is hashed to an index into an array of 16
spinlocks.  That spinlock is taken (with interrupts disabled) around the
operation, which can then be coded non-atomically within the lock.

On UP, all the spinlock manipulation goes away and we simply disable
interrupts around each operation.  In fact gcc eliminates the whole
atomic64_lock variable as well.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 42 insertions, 0 deletions

diff --git a/include/asm-generic/atomic64.h b/include/asm-generic/atomic64.h
new file mode 100644
index 000000000000..b18ce4f9ee3d
--- /dev/null
+++ b/include/asm-generic/atomic64.h
@@ -0,0 +1,42 @@
+/*
+ * Generic implementation of 64-bit atomics using spinlocks,
+ * useful on processors that don't have 64-bit atomic instructions.
+ *
+ * Copyright © 2009 Paul Mackerras, IBM Corp. <paulus@au1.ibm.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+#ifndef _ASM_GENERIC_ATOMIC64_H
+#define _ASM_GENERIC_ATOMIC64_H
+
+typedef struct {
+        long long counter;
+} atomic64_t;
+
+#define ATOMIC64_INIT(i)        { (i) }
+
+extern long long atomic64_read(const atomic64_t *v);
+extern void      atomic64_set(atomic64_t *v, long long i);
+extern void      atomic64_add(long long a, atomic64_t *v);
+extern long long atomic64_add_return(long long a, atomic64_t *v);
+extern void      atomic64_sub(long long a, atomic64_t *v);
+extern long long atomic64_sub_return(long long a, atomic64_t *v);
+extern long long atomic64_dec_if_positive(atomic64_t *v);
+extern long long atomic64_cmpxchg(atomic64_t *v, long long o, long long n);
+extern long long atomic64_xchg(atomic64_t *v, long long new);
+extern int       atomic64_add_unless(atomic64_t *v, long long a, long long u);
+
+#define atomic64_add_negative(a, v)     (atomic64_add_return((a), (v)) < 0)
+#define atomic64_inc(v)                 atomic64_add(1LL, (v))
+#define atomic64_inc_return(v)          atomic64_add_return(1LL, (v))
+#define atomic64_inc_and_test(v)        (atomic64_inc_return(v) == 0)
+#define atomic64_sub_and_test(a, v)     (atomic64_sub_return((a), (v)) == 0)
+#define atomic64_dec(v)                 atomic64_sub(1LL, (v))
+#define atomic64_dec_return(v)          atomic64_sub_return(1LL, (v))
+#define atomic64_dec_and_test(v)        (atomic64_dec_return((v)) == 0)
+#define atomic64_inc_not_zero(v)        atomic64_add_unless((v), 1LL, 0LL)
+
+#endif  /*  _ASM_GENERIC_ATOMIC64_H  */