los_arch_atomic.h

/*
 * Copyright (c) 2013-2019 Huawei Technologies Co., Ltd. All rights reserved.
 * Copyright (c) 2020-2021 Huawei Device Co., Ltd. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
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 * 1. Redistributions of source code must retain the above copyright notice, this list of
 *    conditions and the following disclaimer.
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 * 2. Redistributions in binary form must reproduce the above copyright notice, this list
 *    of conditions and the following disclaimer in the documentation and/or other materials
 *    provided with the distribution.
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 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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 */

#ifndef _LOS_ARCH_ATOMIC_H
#define _LOS_ARCH_ATOMIC_H

#include "los_compiler.h"

#ifdef __cplusplus
#if __cplusplus
extern "C" {
#endif /* __cplusplus */
#endif /* __cplusplus */

/**
 * @ingroup  los_arch_atomic
 * @brief Atomic exchange for 32-bit variable.
 *
 * @par Description:
 * This API is used to implement the atomic exchange for 32-bit variable and return the previous value of the atomic variable.
 * @attention
 * <ul>The pointer v must not be NULL.</ul>
 *
 * @param  v       [IN] The variable pointer.
 * @param  val     [IN] The exchange value.
 *
 * @retval #INT32       The previous value of the atomic variable
 * @par Dependency:
 * <ul><li>los_arch_atomic.h: the header file that contains the API declaration.</li></ul>
 * @see
 */
STATIC INLINE INT32 ArchAtomicXchg32bits(volatile INT32 *v, INT32 val)
{
    INT32 prevVal = 0;
    UINT32 status = 0;

    do {
        __asm__ __volatile__("ldrex   %0, [%3]\n"
                             "strex   %1, %4, [%3]"
                             : "=&r"(prevVal), "=&r"(status), "+m"(*v)
                             : "r"(v), "r"(val)
                             : "cc");
    } while (__builtin_expect(status != 0, 0));

    return prevVal;
}

/**
 * @ingroup  los_arch_atomic
 * @brief Atomic auto-decrement.
 *
 * @par Description:
 * This API is used to implement the atomic auto-decrement and return the result of auto-decrement.
 * @attention
 * <ul>
 * <li>The pointer v must not be NULL.</li>
 * <li>The value which v point to must not be INT_MIN to avoid overflow after reducing 1.</li>
 * </ul>
 *
 * @param  v      [IN] The addSelf variable pointer.
 *
 * @retval #INT32  The return value of variable auto-decrement.
 * @par Dependency:
 * <ul><li>los_arch_atomic.h: the header file that contains the API declaration.</li></ul>
 * @see
 */
STATIC INLINE INT32 ArchAtomicDecRet(volatile INT32 *v)
{
    INT32 val = 0;
    UINT32 status = 0;

    do {
        __asm__ __volatile__("ldrex   %0, [%3]\n"
                             "sub   %0, %0, #1\n"
                             "strex   %1, %0, [%3]"
                             : "=&r"(val), "=&r"(status), "+m"(*v)
                             : "r"(v)
                             : "cc");
    } while (__builtin_expect(status != 0, 0));

    return val;
}

/**
 * @ingroup  los_arch_atomic
 * @brief Atomic exchange for 32-bit variable with compare.
 *
 * @par Description:
 * This API is used to implement the atomic exchange for 32-bit variable, if the value of variable is equal to oldVal.
 * @attention
 * <ul>The pointer v must not be NULL.</ul>
 *
 * @param  v       [IN] The variable pointer.
 * @param  val     [IN] The new value.
 * @param  oldVal  [IN] The old value.
 *
 * @retval TRUE  The previous value of the atomic variable is not equal to oldVal.
 * @retval FALSE The previous value of the atomic variable is equal to oldVal.
 * @par Dependency:
 * <ul><li>los_arch_atomic.h: the header file that contains the API declaration.</li></ul>
 * @see
 */
STATIC INLINE BOOL ArchAtomicCmpXchg32bits(volatile INT32 *v, INT32 val, INT32 oldVal)
{
    INT32 prevVal = 0;
    UINT32 status = 0;

    do {
        __asm__ __volatile__("1: ldrex %0, %2\n"
                             "    mov %1, #0\n"
                             "    cmp %0, %3\n"
                             "    bne 2f\n"
                             "    strex %1, %4, %2\n"
                             "2:"
                             : "=&r"(prevVal), "=&r"(status), "+Q"(*v)
                             : "r"(oldVal), "r"(val)
                             : "cc");
    } while (__builtin_expect(status != 0, 0));

    return prevVal != oldVal;
}

#ifdef __cplusplus
#if __cplusplus
}
#endif /* __cplusplus */
#endif /* __cplusplus */

#endif /* _LOS_ARCH_ATOMIC_H */