nuttx/arch/arm/src/armv7-a/arm_cpupause.c

/****************************************************************************
 * arch/arm/src/armv7-a/arm_cpupause.c
 *
 *   Copyright (C) 2016 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 <stdint.h>

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

#include "up_internal.h"
#include "gic.h"
#include "sched/sched.h"

#ifdef CONFIG_SMP

/****************************************************************************
 * Private Data
 ****************************************************************************/

static spinlock_t g_pause_spinlock[CONFIG_SMP_NCPUS];

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

/****************************************************************************
 * Name: arm_pause_handler
 *
 * Description:
 *   This is the handler for SGI2.  It performs the following operations:
 *
 *   1. It saves the current task state at the head of the current assigned
 *      task list.
 *   2. It waits on a spinlock, then
 *   3. Returns from interrupt, restoring the state of the new task at the
 *      head of the ready to run list.
 *
 * Input Parameters:
 *   Standard interrupt handling
 *
 * Returned Value:
 *   Zero on success; a negated errno value on failure.
 *
 ****************************************************************************/

int arm_pause_handler(int irq, FAR void *context)
{
  FAR struct tcb_s *tcb = this_task();
  int cpu = up_cpu_index();

  /* Update scheduler parameters */

  sched_suspend_scheduler(tcb);

  /* Save the current context at CURRENT_REGS into the TCB at the head of the
   * assigned task list for this CPU.
   */

  up_savestate(tcb->xcp.regs);

  /* Wait for the spinlock to be released */

  spin_lock(&g_pause_spinlock[cpu]);

  /* Restore the exception context of the tcb at the (new) head of the
   * assigned task list.
   */

  tcb = this_task();

  /* Reset scheduler parameters */

  sched_resume_scheduler(tcb);

  /* Then switch contexts.  Any necessary address environment changes will
   * be made when the interrupt returns.
   */

  up_restorestate(tcb->xcp.regs);
  spin_unlock(&g_pause_spinlock[cpu]);
  return OK;
}

/****************************************************************************
 * Name: up_cpu_pause
 *
 * Description:
 *   Save the state of the current task at the head of the
 *   g_assignedtasks[cpu] task list and then pause task execution on the
 *   CPU.
 *
 *   This function is called by the OS when the logic executing on one CPU
 *   needs to modify the state of the g_assignedtasks[cpu] list for another
 *   CPU.
 *
 * Input Parameters:
 *   cpu - The index of the CPU to be stopped/
 *
 * Returned Value:
 *   Zero on success; a negated errno value on failure.
 *
 ****************************************************************************/

int up_cpu_pause(int cpu)
{
  DEBUGASSERT(cpu >= 0 && cpu < CONFIG_SMP_NCPUS && cpu != this_cpu());

  /* Take the spinlock.  The spinlock will cause the SGI2 handler to block
   * on 'cpu'.
   */

  DEBUGASSERT(!spin_islocked(&g_pause_spinlock[cpu]));
  spin_lock(&g_pause_spinlock[cpu]);

  /* Execute SGI2 */

  return arm_cpu_sgi(GIC_IRQ_SGI2, (1 << cpu));
}

/****************************************************************************
 * Name: up_cpu_resume
 *
 * Description:
 *   Restart the cpu after it was paused via up_cpu_pause(), restoring the
 *   state of the task at the head of the g_assignedtasks[cpu] list, and
 *   resume normal tasking.
 *
 *   This function is called after up_cpu_pause in order resume operation of
 *   the CPU after modifying its g_assignedtasks[cpu] list.
 *
 * Input Parameters:
 *   cpu - The index of the CPU being re-started.
 *
 * Returned Value:
 *   Zero on success; a negated errno value on failure.
 *
 ****************************************************************************/

int up_cpu_resume(int cpu)
{
  DEBUGASSERT(cpu >= 0 && cpu < CONFIG_SMP_NCPUS && cpu != this_cpu());

  /* Release the spinlock.  Releasing the spinlock will cause the SGI2
   * handler on 'cpu' to continue and return from interrupt to the newly
   * established thread.
   */

  DEBUGASSERT(spin_islocked(&g_pause_spinlock[cpu]));
  spin_unlock(&g_pause_spinlock[cpu]);
  return OK;
}

#endif /* CONFIG_SMP */