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       1                 :            : /*
       2                 :            :  * Copyright (c) 2016 Wind River Systems, Inc.
       3                 :            :  *
       4                 :            :  * SPDX-License-Identifier: Apache-2.0
       5                 :            :  */
       6                 :            : 
       7                 :            : #include <zephyr/kernel.h>
       8                 :            : #include <zephyr/toolchain.h>
       9                 :            : #include <zephyr/linker/sections.h>
      10                 :            : #include <zephyr/drivers/timer/system_timer.h>
      11                 :            : #include <zephyr/pm/pm.h>
      12                 :            : #include <stdbool.h>
      13                 :            : #include <zephyr/logging/log.h>
      14                 :            : /* private kernel APIs */
      15                 :            : #include <ksched.h>
      16                 :            : #include <kswap.h>
      17                 :            : #include <wait_q.h>
      18                 :            : 
      19                 :            : LOG_MODULE_DECLARE(os, CONFIG_KERNEL_LOG_LEVEL);
      20                 :            : 
      21                 :          0 : void idle(void *unused1, void *unused2, void *unused3)
      22                 :            : {
      23                 :          0 :         ARG_UNUSED(unused1);
      24                 :          0 :         ARG_UNUSED(unused2);
      25                 :          0 :         ARG_UNUSED(unused3);
      26                 :            : 
      27         [ #  # ]:          0 :         __ASSERT_NO_MSG(_current->base.prio >= 0);
      28                 :            : 
      29                 :          0 :         while (true) {
      30                 :            :                 /* SMP systems without a working IPI can't actual
      31                 :            :                  * enter an idle state, because they can't be notified
      32                 :            :                  * of scheduler changes (i.e. threads they should
      33                 :            :                  * run).  They just spin instead, with a minimal
      34                 :            :                  * relaxation loop to prevent hammering the scheduler
      35                 :            :                  * lock and/or timer driver.  This is intended as a
      36                 :            :                  * fallback configuration for new platform bringup.
      37                 :            :                  */
      38                 :          0 :                 if (IS_ENABLED(CONFIG_SMP) && !IS_ENABLED(CONFIG_SCHED_IPI_SUPPORTED)) {
      39                 :            :                         for (volatile int i = 0; i < 100000; i++) {
      40                 :            :                                 /* Empty loop */
      41                 :            :                         }
      42                 :            :                         z_swap_unlocked();
      43                 :            :                 }
      44                 :            : 
      45                 :            :                 /* Note weird API: k_cpu_idle() is called with local
      46                 :            :                  * CPU interrupts masked, and returns with them
      47                 :            :                  * unmasked.  It does not take a spinlock or other
      48                 :            :                  * higher level construct.
      49                 :            :                  */
      50                 :          0 :                 (void) arch_irq_lock();
      51                 :            : 
      52                 :            : #ifdef CONFIG_PM
      53                 :            :                 _kernel.idle = z_get_next_timeout_expiry();
      54                 :            : 
      55                 :            :                 /*
      56                 :            :                  * Call the suspend hook function of the soc interface
      57                 :            :                  * to allow entry into a low power state. The function
      58                 :            :                  * returns false if low power state was not entered, in
      59                 :            :                  * which case, kernel does normal idle processing.
      60                 :            :                  *
      61                 :            :                  * This function is entered with interrupts disabled.
      62                 :            :                  * If a low power state was entered, then the hook
      63                 :            :                  * function should enable interrupts before exiting.
      64                 :            :                  * This is because the kernel does not do its own idle
      65                 :            :                  * processing in those cases i.e. skips k_cpu_idle().
      66                 :            :                  * The kernel's idle processing re-enables interrupts
      67                 :            :                  * which is essential for the kernel's scheduling
      68                 :            :                  * logic.
      69                 :            :                  */
      70                 :            :                 if (k_is_pre_kernel() || !pm_system_suspend(_kernel.idle)) {
      71                 :            :                         k_cpu_idle();
      72                 :            :                 }
      73                 :            : #else
      74                 :          0 :                 k_cpu_idle();
      75                 :            : #endif /* CONFIG_PM */
      76                 :            : 
      77                 :            : #if !defined(CONFIG_PREEMPT_ENABLED)
      78                 :            : # if !defined(CONFIG_USE_SWITCH) || defined(CONFIG_SPARC)
      79                 :            :                 /* A legacy mess: the idle thread is by definition
      80                 :            :                  * preemptible as far as the modern scheduler is
      81                 :            :                  * concerned, but older platforms use
      82                 :            :                  * CONFIG_PREEMPT_ENABLED=n as an optimization hint
      83                 :            :                  * that interrupt exit always returns to the
      84                 :            :                  * interrupted context.  So in that setup we need to
      85                 :            :                  * explicitly yield in the idle thread otherwise
      86                 :            :                  * nothing else will run once it starts.
      87                 :            :                  */
      88                 :            :                 if (_kernel.ready_q.cache != _current) {
      89                 :            :                         z_swap_unlocked();
      90                 :            :                 }
      91                 :            : # endif /* !defined(CONFIG_USE_SWITCH) || defined(CONFIG_SPARC) */
      92                 :            : #endif /* !defined(CONFIG_PREEMPT_ENABLED) */
      93                 :            :         }
      94                 :            : }
      95                 :            : 
      96                 :          0 : void __weak arch_spin_relax(void)
      97                 :            : {
      98         [ #  # ]:          0 :         __ASSERT(!arch_irq_unlocked(arch_irq_lock()),
      99                 :            :                  "this is meant to be called with IRQs disabled");
     100                 :            : 
     101                 :          0 :         arch_nop();
     102                 :          0 : }