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RISC-V: Atomic and Locking Code
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This contains all the code that directly interfaces with the RISC-V
memory model.  While this code corforms to the current RISC-V ISA
specifications (user 2.2 and priv 1.10), the memory model is somewhat
underspecified in those documents.  There is a working group that hopes
to produce a formal memory model by the end of the year, but my
understanding is that the basic definitions we're relying on here won't
change significantly.

Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Palmer Dabbelt <palmer@dabbelt.com>
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palmer-dabbelt committed Sep 26, 2017
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375 changes: 375 additions & 0 deletions arch/riscv/include/asm/atomic.h
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/*
* Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
* Copyright (C) 2012 Regents of the University of California
* Copyright (C) 2017 SiFive
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public Licence
* as published by the Free Software Foundation; either version
* 2 of the Licence, or (at your option) any later version.
*/

#ifndef _ASM_RISCV_ATOMIC_H
#define _ASM_RISCV_ATOMIC_H

#ifdef CONFIG_GENERIC_ATOMIC64
# include <asm-generic/atomic64.h>
#else
# if (__riscv_xlen < 64)
# error "64-bit atomics require XLEN to be at least 64"
# endif
#endif

#include <asm/cmpxchg.h>
#include <asm/barrier.h>

#define ATOMIC_INIT(i) { (i) }
static __always_inline int atomic_read(const atomic_t *v)
{
return READ_ONCE(v->counter);
}
static __always_inline void atomic_set(atomic_t *v, int i)
{
WRITE_ONCE(v->counter, i);
}

#ifndef CONFIG_GENERIC_ATOMIC64
#define ATOMIC64_INIT(i) { (i) }
static __always_inline long atomic64_read(const atomic64_t *v)
{
return READ_ONCE(v->counter);
}
static __always_inline void atomic64_set(atomic64_t *v, long i)
{
WRITE_ONCE(v->counter, i);
}
#endif

/*
* First, the atomic ops that have no ordering constraints and therefor don't
* have the AQ or RL bits set. These don't return anything, so there's only
* one version to worry about.
*/
#define ATOMIC_OP(op, asm_op, c_op, I, asm_type, c_type, prefix) \
static __always_inline void atomic##prefix##_##op(c_type i, atomic##prefix##_t *v) \
{ \
__asm__ __volatile__ ( \
"amo" #asm_op "." #asm_type " zero, %1, %0" \
: "+A" (v->counter) \
: "r" (I) \
: "memory"); \
}

#ifdef CONFIG_GENERIC_ATOMIC64
#define ATOMIC_OPS(op, asm_op, c_op, I) \
ATOMIC_OP (op, asm_op, c_op, I, w, int, )
#else
#define ATOMIC_OPS(op, asm_op, c_op, I) \
ATOMIC_OP (op, asm_op, c_op, I, w, int, ) \
ATOMIC_OP (op, asm_op, c_op, I, d, long, 64)
#endif

ATOMIC_OPS(add, add, +, i)
ATOMIC_OPS(sub, add, +, -i)
ATOMIC_OPS(and, and, &, i)
ATOMIC_OPS( or, or, |, i)
ATOMIC_OPS(xor, xor, ^, i)

#undef ATOMIC_OP
#undef ATOMIC_OPS

/*
* Atomic ops that have ordered, relaxed, acquire, and relese variants.
* There's two flavors of these: the arithmatic ops have both fetch and return
* versions, while the logical ops only have fetch versions.
*/
#define ATOMIC_FETCH_OP(op, asm_op, c_op, I, asm_or, c_or, asm_type, c_type, prefix) \
static __always_inline c_type atomic##prefix##_fetch_##op##c_or(c_type i, atomic##prefix##_t *v) \
{ \
register c_type ret; \
__asm__ __volatile__ ( \
"amo" #asm_op "." #asm_type #asm_or " %1, %2, %0" \
: "+A" (v->counter), "=r" (ret) \
: "r" (I) \
: "memory"); \
return ret; \
}

#define ATOMIC_OP_RETURN(op, asm_op, c_op, I, asm_or, c_or, asm_type, c_type, prefix) \
static __always_inline c_type atomic##prefix##_##op##_return##c_or(c_type i, atomic##prefix##_t *v) \
{ \
return atomic##prefix##_fetch_##op##c_or(i, v) c_op I; \
}

#ifdef CONFIG_GENERIC_ATOMIC64
#define ATOMIC_OPS(op, asm_op, c_op, I, asm_or, c_or) \
ATOMIC_FETCH_OP (op, asm_op, c_op, I, asm_or, c_or, w, int, ) \
ATOMIC_OP_RETURN(op, asm_op, c_op, I, asm_or, c_or, w, int, )
#else
#define ATOMIC_OPS(op, asm_op, c_op, I, asm_or, c_or) \
ATOMIC_FETCH_OP (op, asm_op, c_op, I, asm_or, c_or, w, int, ) \
ATOMIC_OP_RETURN(op, asm_op, c_op, I, asm_or, c_or, w, int, ) \
ATOMIC_FETCH_OP (op, asm_op, c_op, I, asm_or, c_or, d, long, 64) \
ATOMIC_OP_RETURN(op, asm_op, c_op, I, asm_or, c_or, d, long, 64)
#endif

ATOMIC_OPS(add, add, +, i, , _relaxed)
ATOMIC_OPS(add, add, +, i, .aq , _acquire)
ATOMIC_OPS(add, add, +, i, .rl , _release)
ATOMIC_OPS(add, add, +, i, .aqrl, )

ATOMIC_OPS(sub, add, +, -i, , _relaxed)
ATOMIC_OPS(sub, add, +, -i, .aq , _acquire)
ATOMIC_OPS(sub, add, +, -i, .rl , _release)
ATOMIC_OPS(sub, add, +, -i, .aqrl, )

#undef ATOMIC_OPS

#ifdef CONFIG_GENERIC_ATOMIC64
#define ATOMIC_OPS(op, asm_op, c_op, I, asm_or, c_or) \
ATOMIC_FETCH_OP(op, asm_op, c_op, I, asm_or, c_or, w, int, )
#else
#define ATOMIC_OPS(op, asm_op, c_op, I, asm_or, c_or) \
ATOMIC_FETCH_OP(op, asm_op, c_op, I, asm_or, c_or, w, int, ) \
ATOMIC_FETCH_OP(op, asm_op, c_op, I, asm_or, c_or, d, long, 64)
#endif

ATOMIC_OPS(and, and, &, i, , _relaxed)
ATOMIC_OPS(and, and, &, i, .aq , _acquire)
ATOMIC_OPS(and, and, &, i, .rl , _release)
ATOMIC_OPS(and, and, &, i, .aqrl, )

ATOMIC_OPS( or, or, |, i, , _relaxed)
ATOMIC_OPS( or, or, |, i, .aq , _acquire)
ATOMIC_OPS( or, or, |, i, .rl , _release)
ATOMIC_OPS( or, or, |, i, .aqrl, )

ATOMIC_OPS(xor, xor, ^, i, , _relaxed)
ATOMIC_OPS(xor, xor, ^, i, .aq , _acquire)
ATOMIC_OPS(xor, xor, ^, i, .rl , _release)
ATOMIC_OPS(xor, xor, ^, i, .aqrl, )

#undef ATOMIC_OPS

#undef ATOMIC_FETCH_OP
#undef ATOMIC_OP_RETURN

/*
* The extra atomic operations that are constructed from one of the core
* AMO-based operations above (aside from sub, which is easier to fit above).
* These are required to perform a barrier, but they're OK this way because
* atomic_*_return is also required to perform a barrier.
*/
#define ATOMIC_OP(op, func_op, comp_op, I, c_type, prefix) \
static __always_inline bool atomic##prefix##_##op(c_type i, atomic##prefix##_t *v) \
{ \
return atomic##prefix##_##func_op##_return(i, v) comp_op I; \
}

#ifdef CONFIG_GENERIC_ATOMIC64
#define ATOMIC_OPS(op, func_op, comp_op, I) \
ATOMIC_OP (op, func_op, comp_op, I, int, )
#else
#define ATOMIC_OPS(op, func_op, comp_op, I) \
ATOMIC_OP (op, func_op, comp_op, I, int, ) \
ATOMIC_OP (op, func_op, comp_op, I, long, 64)
#endif

ATOMIC_OPS(add_and_test, add, ==, 0)
ATOMIC_OPS(sub_and_test, sub, ==, 0)
ATOMIC_OPS(add_negative, add, <, 0)

#undef ATOMIC_OP
#undef ATOMIC_OPS

#define ATOMIC_OP(op, func_op, c_op, I, c_type, prefix) \
static __always_inline void atomic##prefix##_##op(atomic##prefix##_t *v) \
{ \
atomic##prefix##_##func_op(I, v); \
}

#define ATOMIC_FETCH_OP(op, func_op, c_op, I, c_type, prefix) \
static __always_inline c_type atomic##prefix##_fetch_##op(atomic##prefix##_t *v) \
{ \
return atomic##prefix##_fetch_##func_op(I, v); \
}

#define ATOMIC_OP_RETURN(op, asm_op, c_op, I, c_type, prefix) \
static __always_inline c_type atomic##prefix##_##op##_return(atomic##prefix##_t *v) \
{ \
return atomic##prefix##_fetch_##op(v) c_op I; \
}

#ifdef CONFIG_GENERIC_ATOMIC64
#define ATOMIC_OPS(op, asm_op, c_op, I) \
ATOMIC_OP (op, asm_op, c_op, I, int, ) \
ATOMIC_FETCH_OP (op, asm_op, c_op, I, int, ) \
ATOMIC_OP_RETURN(op, asm_op, c_op, I, int, )
#else
#define ATOMIC_OPS(op, asm_op, c_op, I) \
ATOMIC_OP (op, asm_op, c_op, I, int, ) \
ATOMIC_FETCH_OP (op, asm_op, c_op, I, int, ) \
ATOMIC_OP_RETURN(op, asm_op, c_op, I, int, ) \
ATOMIC_OP (op, asm_op, c_op, I, long, 64) \
ATOMIC_FETCH_OP (op, asm_op, c_op, I, long, 64) \
ATOMIC_OP_RETURN(op, asm_op, c_op, I, long, 64)
#endif

ATOMIC_OPS(inc, add, +, 1)
ATOMIC_OPS(dec, add, +, -1)

#undef ATOMIC_OPS
#undef ATOMIC_OP
#undef ATOMIC_FETCH_OP
#undef ATOMIC_OP_RETURN

#define ATOMIC_OP(op, func_op, comp_op, I, prefix) \
static __always_inline bool atomic##prefix##_##op(atomic##prefix##_t *v) \
{ \
return atomic##prefix##_##func_op##_return(v) comp_op I; \
}

ATOMIC_OP(inc_and_test, inc, ==, 0, )
ATOMIC_OP(dec_and_test, dec, ==, 0, )
#ifndef CONFIG_GENERIC_ATOMIC64
ATOMIC_OP(inc_and_test, inc, ==, 0, 64)
ATOMIC_OP(dec_and_test, dec, ==, 0, 64)
#endif

#undef ATOMIC_OP

/* This is required to provide a barrier on success. */
static __always_inline int __atomic_add_unless(atomic_t *v, int a, int u)
{
int prev, rc;

__asm__ __volatile__ (
"0:\n\t"
"lr.w.aqrl %[p], %[c]\n\t"
"beq %[p], %[u], 1f\n\t"
"add %[rc], %[p], %[a]\n\t"
"sc.w.aqrl %[rc], %[rc], %[c]\n\t"
"bnez %[rc], 0b\n\t"
"1:"
: [p]"=&r" (prev), [rc]"=&r" (rc), [c]"+A" (v->counter)
: [a]"r" (a), [u]"r" (u)
: "memory");
return prev;
}

#ifndef CONFIG_GENERIC_ATOMIC64
static __always_inline long __atomic64_add_unless(atomic64_t *v, long a, long u)
{
long prev, rc;

__asm__ __volatile__ (
"0:\n\t"
"lr.d.aqrl %[p], %[c]\n\t"
"beq %[p], %[u], 1f\n\t"
"add %[rc], %[p], %[a]\n\t"
"sc.d.aqrl %[rc], %[rc], %[c]\n\t"
"bnez %[rc], 0b\n\t"
"1:"
: [p]"=&r" (prev), [rc]"=&r" (rc), [c]"+A" (v->counter)
: [a]"r" (a), [u]"r" (u)
: "memory");
return prev;
}

static __always_inline int atomic64_add_unless(atomic64_t *v, long a, long u)
{
return __atomic64_add_unless(v, a, u) != u;
}
#endif

/*
* The extra atomic operations that are constructed from one of the core
* LR/SC-based operations above.
*/
static __always_inline int atomic_inc_not_zero(atomic_t *v)
{
return __atomic_add_unless(v, 1, 0);
}

#ifndef CONFIG_GENERIC_ATOMIC64
static __always_inline long atomic64_inc_not_zero(atomic64_t *v)
{
return atomic64_add_unless(v, 1, 0);
}
#endif

/*
* atomic_{cmp,}xchg is required to have exactly the same ordering semantics as
* {cmp,}xchg and the operations that return, so they need a barrier. We just
* use the other implementations directly.
*/
#define ATOMIC_OP(c_t, prefix, c_or, size, asm_or) \
static __always_inline c_t atomic##prefix##_cmpxchg##c_or(atomic##prefix##_t *v, c_t o, c_t n) \
{ \
return __cmpxchg(&(v->counter), o, n, size, asm_or, asm_or); \
} \
static __always_inline c_t atomic##prefix##_xchg##c_or(atomic##prefix##_t *v, c_t n) \
{ \
return __xchg(n, &(v->counter), size, asm_or); \
}

#ifdef CONFIG_GENERIC_ATOMIC64
#define ATOMIC_OPS(c_or, asm_or) \
ATOMIC_OP( int, , c_or, 4, asm_or)
#else
#define ATOMIC_OPS(c_or, asm_or) \
ATOMIC_OP( int, , c_or, 4, asm_or) \
ATOMIC_OP(long, 64, c_or, 8, asm_or)
#endif

ATOMIC_OPS( , .aqrl)
ATOMIC_OPS(_acquire, .aq)
ATOMIC_OPS(_release, .rl)
ATOMIC_OPS(_relaxed, )

#undef ATOMIC_OPS
#undef ATOMIC_OP

static __always_inline int atomic_sub_if_positive(atomic_t *v, int offset)
{
int prev, rc;

__asm__ __volatile__ (
"0:\n\t"
"lr.w.aqrl %[p], %[c]\n\t"
"sub %[rc], %[p], %[o]\n\t"
"bltz %[rc], 1f\n\t"
"sc.w.aqrl %[rc], %[rc], %[c]\n\t"
"bnez %[rc], 0b\n\t"
"1:"
: [p]"=&r" (prev), [rc]"=&r" (rc), [c]"+A" (v->counter)
: [o]"r" (offset)
: "memory");
return prev - offset;
}

#define atomic_dec_if_positive(v) atomic_sub_if_positive(v, 1)

#ifndef CONFIG_GENERIC_ATOMIC64
static __always_inline long atomic64_sub_if_positive(atomic64_t *v, int offset)
{
long prev, rc;

__asm__ __volatile__ (
"0:\n\t"
"lr.d.aqrl %[p], %[c]\n\t"
"sub %[rc], %[p], %[o]\n\t"
"bltz %[rc], 1f\n\t"
"sc.d.aqrl %[rc], %[rc], %[c]\n\t"
"bnez %[rc], 0b\n\t"
"1:"
: [p]"=&r" (prev), [rc]"=&r" (rc), [c]"+A" (v->counter)
: [o]"r" (offset)
: "memory");
return prev - offset;
}

#define atomic64_dec_if_positive(v) atomic64_sub_if_positive(v, 1)
#endif

#endif /* _ASM_RISCV_ATOMIC_H */
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