nuttx/arch/arm/include/spinlock.h

/****************************************************************************
 * arch/arm/include/spinlock.h
 *
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.  The
 * ASF licenses this file to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance with the
 * License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
 * License for the specific language governing permissions and limitations
 * under the License.
 *
 ****************************************************************************/

#ifndef __ARCH_ARM_INCLUDE_SPINLOCK_H
#define __ARCH_ARM_INCLUDE_SPINLOCK_H

/****************************************************************************
 * Included Files
 ****************************************************************************/

#ifndef __ASSEMBLY__
#  include <stdint.h>
#endif /* __ASSEMBLY__ */

/****************************************************************************
 * Pre-processor Prototypes
 ****************************************************************************/

/* Spinlock states */

#define SP_UNLOCKED 0  /* The Un-locked state */
#define SP_LOCKED   1  /* The Locked state */

/* Memory barriers for use with NuttX spinlock logic
 *
 * Data Memory Barrier (DMB) acts as a memory barrier. It ensures that all
 * explicit memory accesses that appear in program order before the DMB
 * instruction are observed before any explicit memory accesses that appear
 * in program order after the DMB instruction. It does not affect the
 * ordering of any other instructions executing on the processor
 *
 *   dmb st - Data memory barrier.  Wait for stores to complete.
 *
 * Data Synchronization Barrier (DSB) acts as a special kind of memory
 * barrier. No instruction in program order after this instruction executes
 * until this instruction completes. This instruction completes when: (1) All
 * explicit memory accesses before this instruction complete, and (2) all
 * Cache, Branch predictor and TLB maintenance operations before this
 * instruction complete.
 *
 *   dsb sy - Data syncrhonization barrier.  Assures that the CPU waits until
 *            all memory accesses are complete
 */

#define SP_DSB() __asm__ __volatile__ ("dsb sy" : : : "memory")
#define SP_DMB() __asm__ __volatile__ ("dmb st" : : : "memory")

#ifdef CONFIG_ARM_HAVE_WFE_SEV
#define SP_WFE() __asm__ __volatile__ ("wfe" : : : "memory")
#define SP_SEV() __asm__ __volatile__ ("sev" : : : "memory")
#endif

/****************************************************************************
 * Public Types
 ****************************************************************************/

#ifndef __ASSEMBLY__

/* The Type of a spinlock.
 *
 * ARMv6 architecture introduced the concept of exclusive accesses to memory
 * locations in the form of the Load-Exclusive (LDREX) and Store-Exclusive
 * (STREX) instructions in ARM and Thumb instruction sets.  ARMv6K extended
 * this to included byte, halfword, and doubleword variants of LDREX and
 * STREX.  ARMv7-M supports byte and halfword, but not the doubleword variant
 * (ARMv6-M does not support exclusive access).
 *
 * ARM architectures prior to ARMv6 supported SWP and SWPB instructions that
 * atomically swap a 32-bit word for byte value between a register and a
 * memory location.  From the ARMv6 architecture, ARM deprecates the use
 * of SWP and SWPB.
 */

typedef uint8_t spinlock_t;

/****************************************************************************
 * Public Function Prototypes
 ****************************************************************************/

/****************************************************************************
 * Name: up_testset
 *
 * Description:
 *   Perform an atomic test and set operation on the provided spinlock.
 *
 *   This function must be provided via the architecture-specific logic.
 *
 * Input Parameters:
 *   lock - The address of spinlock object.
 *
 * Returned Value:
 *   The spinlock is always locked upon return.  The value of previous value
 *   of the spinlock variable is returned, either SP_LOCKED if the spinlock
 *   as previously locked (meaning that the test-and-set operation failed to
 *   obtain the lock) or SP_UNLOCKED if the spinlock was previously unlocked
 *   (meaning that we successfully obtained the lock)
 *
 ****************************************************************************/

#if defined(CONFIG_ARCH_HAVE_TESTSET) \
    && !defined(CONFIG_ARCH_CHIP_LC823450) \
    && !defined(CONFIG_ARCH_CHIP_CXD56XX) \
    && !defined(CONFIG_ARCH_CHIP_RP2040)
static inline_function spinlock_t up_testset(FAR volatile spinlock_t *lock)
{
  spinlock_t ret = SP_UNLOCKED;

  __asm__ __volatile__
  (
    "1:                    \n"
    "ldrexb   %0, [%2]     \n"
    "cmp      %0, %1       \n"
    "beq      2f           \n"
    "strexb   %0, %1, [%2] \n"
    "cmp      %0, %1       \n"
    "beq      1b           \n"
    "dmb                   \n"
    "2:                    \n"
    : "+r" (ret)
    : "r" (SP_LOCKED), "r" (lock)
    : "memory"
  );

  return ret;
}
#endif

/* See prototype in nuttx/include/nuttx/spinlock.h */

#endif /* __ASSEMBLY__ */
#endif /* __ARCH_ARM_INCLUDE_SPINLOCK_H */