core/cortex-m/atomic.h

/* Copyright (c) 2012 The Chromium OS Authors. All rights reserved.
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

/* Atomic operations for ARMv7 */

#ifndef __CROS_EC_ATOMIC_H
#define __CROS_EC_ATOMIC_H

#include "common.h"

/**
 * Implements atomic arithmetic operations on 32-bit integers.
 *
 * It used load/store exclusive.
 * If you write directly the integer used as an atomic variable,
 * you must either clear explicitly the exclusive monitor (using clrex)
 * or do it in exception context (which clears the monitor).
 */
#define ATOMIC_OP(asm_op,a,v) do {                              \
	uint32_t reg0, reg1;                                    \
	                                                        \
	__asm__ __volatile__("1: ldrex   %0, [%2]\n"            \
	                        #asm_op" %0, %0, %3\n"          \
	                     "   strex   %1, %0, [%2]\n"        \
	                     "   teq     %1, #0\n"              \
	                     "   bne     1b"                    \
	                     : "=&r" (reg0), "=&r" (reg1)       \
	                     : "r" (a), "r" (v) : "cc");        \
} while (0);

static inline void atomic_clear(uint32_t *addr, uint32_t bits)
{
	ATOMIC_OP(bic, addr, bits);
}

static inline void atomic_or(uint32_t *addr, uint32_t bits)
{
	ATOMIC_OP(orr, addr, bits);
}

static inline void atomic_add(uint32_t *addr, uint32_t value)
{
	ATOMIC_OP(add, addr, value);
}

static inline void atomic_sub(uint32_t *addr, uint32_t value)
{
	ATOMIC_OP(sub, addr, value);
}

static inline uint32_t atomic_read_clear(uint32_t *addr)
{
	uint32_t ret, tmp;

	__asm__ __volatile__("   mov     %3, #0\n"
	                     "1: ldrex   %0, [%2]\n"
	                     "   strex   %1, %3, [%2]\n"
	                     "   teq     %1, #0\n"
	                     "   bne     1b"
	                     : "=&r" (ret), "=&r" (tmp)
	                     : "r" (addr), "r" (0) : "cc");

	return ret;
}
#endif  /* __CROS_EC_ATOMIC_H */