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Gregory Nutt
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arch/xtensa/src/common/xtensa_cpupause.c
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arch/xtensa/src/common/xtensa_cpupause.c
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/****************************************************************************
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* arch/xtensa/src/common/xtensa_cpupause.c
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*
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* Copyright (C) 2016 Gregory Nutt. All rights reserved.
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* Author: Gregory Nutt <gnutt@nuttx.org>
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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* 3. Neither the name NuttX nor the names of its contributors may be
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* used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*
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****************************************************************************/
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/****************************************************************************
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* Included Files
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****************************************************************************/
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#include <nuttx/config.h>
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#include <stdint.h>
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#include <nuttx/arch.h>
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#include <nuttx/sched.h>
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#include <nuttx/spinlock.h>
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#include "xtensa.h"
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#include "sched/sched.h"
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#ifdef CONFIG_SMP
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/****************************************************************************
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* Private Data
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****************************************************************************/
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static spinlock_t g_cpu_wait[CONFIG_SMP_NCPUS];
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static spinlock_t g_cpu_paused[CONFIG_SMP_NCPUS];
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: xtensa_pause_handler
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*
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* Description:
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* This is the handler for CPU_INTCODE_PAUSE CPU interrupt. This
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* implements up_cpu_pause() by performing the following operations:
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*
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* 1. The current task state at the head of the current assigned task
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* list was saved when the interrupt was entered.
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* 2. This function simply waits on a spinlock, then returns.
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* 3. Upon return, the interrupt exit logic will restore the state of
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* the new task at the head of the ready to run list.
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*
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* Input Parameters:
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* None
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*
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* Returned Value:
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* None
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*
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****************************************************************************/
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void xtensa_pause_handler(void)
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{
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FAR struct tcb_s *otcb = this_task();
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FAR struct tcb_s *ntcb;
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int cpu = up_cpu_index();
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/* Update scheduler parameters */
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sched_suspend_scheduler(otcb);
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/* Copy the CURRENT_REGS into the OLD TCB (otcb). The co-processor state
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* will be saved as part of the return from xtensa_irq_dispatch().
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*/
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xtensa_savestate(otcb->xcp.regs);
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/* Wait for the spinlock to be released */
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spin_unlock(&g_cpu_paused[cpu]);
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spin_lock(&g_cpu_wait[cpu]);
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/* Upon return, we will restore the exception context of the new TCB
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* (ntcb) at the head of the ready-to-run task list.
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*/
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ntcb = this_task();
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/* Reset scheduler parameters */
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sched_resume_scheduler(ntcb);
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/* Did the task at the head of the list change? */
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if (otcb != ntcb)
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{
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/* Set CURRENT_REGS to the context save are of the new TCB to start.
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* This will inform the return-from-interrupt logic that a context
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* switch must be performed.
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*/
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xtensa_restorestate(ntcb->xcp.regs);
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}
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spin_unlock(&g_cpu_wait[cpu]);
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}
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/****************************************************************************
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* Name: up_cpu_pause
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*
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* Description:
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* Save the state of the current task at the head of the
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* g_assignedtasks[cpu] task list and then pause task execution on the
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* CPU.
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*
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* This function is called by the OS when the logic executing on one CPU
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* needs to modify the state of the g_assignedtasks[cpu] list for another
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* CPU.
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*
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* Input Parameters:
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* cpu - The index of the CPU to be stopped.
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*
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* Returned Value:
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* Zero on success; a negated errno value on failure.
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*
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****************************************************************************/
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int up_cpu_pause(int cpu)
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{
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int ret;
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DEBUGASSERT(cpu >= 0 && cpu < CONFIG_SMP_NCPUS && cpu != this_cpu());
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/* Take the both spinlocks. The g_cpu_wait spinlock will prevent the SGI2
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* handler from returning until up_cpu_resume() is called; g_cpu_paused
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* is a handshake that will prefent this function from returning until
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* the CPU is actually paused.
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*/
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DEBUGASSERT(!spin_islocked(&g_cpu_wait[cpu]) &&
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!spin_islocked(&g_cpu_paused[cpu]));
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spin_lock(&g_cpu_wait[cpu]);
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spin_lock(&g_cpu_paused[cpu]);
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/* Execute SGI2 */
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ret = xtensa_cpu_interrupt(cpu, CPU_INTCODE_PAUSE);
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if (ret < 0)
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{
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/* What happened? Unlock the g_cpu_wait spinlock */
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spin_unlock(&g_cpu_wait[cpu]);
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}
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else
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{
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/* Wait for the other CPU to unlock g_cpu_paused meaning that
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* it is fully paused and ready for up_cpu_resume();
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*/
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spin_lock(&g_cpu_paused[cpu]);
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}
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spin_unlock(&g_cpu_paused[cpu]);
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/* On successful return g_cpu_wait will be locked, the other CPU will be
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* spinninf on g_cpu_wait and will not continue until g_cpu_resume() is
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* called. g_cpu_paused will be unlocked in any case.
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*/
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return ret;
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}
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/****************************************************************************
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* Name: up_cpu_resume
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*
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* Description:
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* Restart the cpu after it was paused via up_cpu_pause(), restoring the
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* state of the task at the head of the g_assignedtasks[cpu] list, and
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* resume normal tasking.
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*
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* This function is called after up_cpu_pause in order resume operation of
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* the CPU after modifying its g_assignedtasks[cpu] list.
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*
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* Input Parameters:
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* cpu - The index of the CPU being re-started.
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*
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* Returned Value:
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* Zero on success; a negated errno value on failure.
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*
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****************************************************************************/
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int up_cpu_resume(int cpu)
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{
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DEBUGASSERT(cpu >= 0 && cpu < CONFIG_SMP_NCPUS && cpu != this_cpu());
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/* Release the spinlock. Releasing the spinlock will cause the SGI2
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* handler on 'cpu' to continue and return from interrupt to the newly
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* established thread.
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*/
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DEBUGASSERT(spin_islocked(&g_cpu_wait[cpu]) &&
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!spin_islocked(&g_cpu_paused[cpu]));
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spin_unlock(&g_cpu_wait[cpu]);
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return OK;
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}
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#endif /* CONFIG_SMP */
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