/****************************************************************************
 * sched/irq/irq_csection.c
 *
 *   Copyright (C) 2007-2008, 2010 Gregory Nutt. All rights reserved.
 *   Author: Gregory Nutt <gnutt@nuttx.org>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 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.
 * 3. Neither the name NuttX nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 ****************************************************************************/

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

#include <nuttx/config.h>

#include <nuttx/spinlock.h>
#include <arch/irq.h>

#include "sched/sched.h"
#include "irq/irq.h"

#ifdef CONFIG_SMP

/****************************************************************************
 * Public Data
 ****************************************************************************/
/* This is the spinlock that enforces critical sections when interrupts are
 * disabled.
 */

spinlock_t g_cpu_irqlock = SP_UNLOCKED;

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name: enter_critical_section
 *
 * Description:
 *   Take the CPU IRQ lock and disable interrupts on all CPUs.  A thread-
 *   specific counter is increment to indicate that the thread has IRQs
 *   disabled and to support nested calls to enter_critical_section().
 *
 ****************************************************************************/

irqstate_t enter_critical_section(void)
{
  FAR struct tcb_s *rtcb = this_task();

  /* Do we already have interrupts disabled? */

  if (rtcb->irqcount > 0)
    {
      /* Yes... make sure that the spinlock is set and increment the IRQ
       * lock count.
       */

      DEBUGASSERT(g_cpu_irqlock == SP_LOCKED && rtcb->irqcount < INT16_MAX);
      rtcb->irqcount++;
    }
  else
    {
      /* NO.. Take the spinlock to get exclusive access and set the lock
       * count to 1.
       */

      spin_lock(&g_cpu_irqlock);
      rtcb->irqcount = 1;
    }

  /* Then disable interrupts (if they have not already been disabeld) */

  return irqsave();
}

/****************************************************************************
 * Name: leave_critical_section
 *
 * Description:
 *   Decrement the IRQ lock count and if it decrements to zero then release
 *   the spinlock.
 *
 ****************************************************************************/

void leave_critical_section(irqstate_t flags)
{
  FAR struct tcb_s *rtcb = this_task();

  DEBUGASSERT(rtcb->irqcount > 0);

  /* Will we still have interrupts disabled after decrementing the count? */

  if (rtcb->irqcount > 1)
    {
      /* Yes... make sure that the spinlock is set */

      DEBUGASSERT(g_cpu_irqlock == SP_LOCKED);
      rtcb->irqcount--;
    }
  else
    {
      /* NO.. Take the spinlock to get exclusive access. */

      rtcb->irqcount = 0;
      spin_unlock(g_cpu_irqlock);
    }

  /* Restore the previous interrupt state which may still be interrupts
   * disabled (but we don't have a mechanism to verify that now)
   */

  irqrestore(flags);
}

#endif /* CONFIG_SMP */