1 /* 2 * The idle loop for all SuperH platforms. 3 * 4 * Copyright (C) 2002 - 2009 Paul Mundt 5 * 6 * This file is subject to the terms and conditions of the GNU General Public 7 * License. See the file "COPYING" in the main directory of this archive 8 * for more details. 9 */ 10 #include <linux/module.h> 11 #include <linux/init.h> 12 #include <linux/mm.h> 13 #include <linux/pm.h> 14 #include <linux/tick.h> 15 #include <linux/preempt.h> 16 #include <linux/thread_info.h> 17 #include <linux/irqflags.h> 18 #include <linux/smp.h> 19 #include <asm/pgalloc.h> 20 #include <asm/system.h> 21 #include <asm/atomic.h> 22 #include <asm/smp.h> 23 24 void (*pm_idle)(void) = NULL; 25 26 static int hlt_counter; 27 28 static int __init nohlt_setup(char *__unused) 29 { 30 hlt_counter = 1; 31 return 1; 32 } 33 __setup("nohlt", nohlt_setup); 34 35 static int __init hlt_setup(char *__unused) 36 { 37 hlt_counter = 0; 38 return 1; 39 } 40 __setup("hlt", hlt_setup); 41 42 static inline int hlt_works(void) 43 { 44 return !hlt_counter; 45 } 46 47 /* 48 * On SMP it's slightly faster (but much more power-consuming!) 49 * to poll the ->work.need_resched flag instead of waiting for the 50 * cross-CPU IPI to arrive. Use this option with caution. 51 */ 52 static void poll_idle(void) 53 { 54 local_irq_enable(); 55 while (!need_resched()) 56 cpu_relax(); 57 } 58 59 void default_idle(void) 60 { 61 if (hlt_works()) { 62 clear_thread_flag(TIF_POLLING_NRFLAG); 63 smp_mb__after_clear_bit(); 64 65 set_bl_bit(); 66 if (!need_resched()) { 67 local_irq_enable(); 68 cpu_sleep(); 69 } else 70 local_irq_enable(); 71 72 set_thread_flag(TIF_POLLING_NRFLAG); 73 clear_bl_bit(); 74 } else 75 poll_idle(); 76 } 77 78 /* 79 * The idle thread. There's no useful work to be done, so just try to conserve 80 * power and have a low exit latency (ie sit in a loop waiting for somebody to 81 * say that they'd like to reschedule) 82 */ 83 void cpu_idle(void) 84 { 85 unsigned int cpu = smp_processor_id(); 86 87 set_thread_flag(TIF_POLLING_NRFLAG); 88 89 /* endless idle loop with no priority at all */ 90 while (1) { 91 tick_nohz_stop_sched_tick(1); 92 93 while (!need_resched()) { 94 check_pgt_cache(); 95 rmb(); 96 97 if (cpu_is_offline(cpu)) 98 play_dead(); 99 100 local_irq_disable(); 101 /* Don't trace irqs off for idle */ 102 stop_critical_timings(); 103 pm_idle(); 104 /* 105 * Sanity check to ensure that pm_idle() returns 106 * with IRQs enabled 107 */ 108 WARN_ON(irqs_disabled()); 109 start_critical_timings(); 110 } 111 112 tick_nohz_restart_sched_tick(); 113 preempt_enable_no_resched(); 114 schedule(); 115 preempt_disable(); 116 } 117 } 118 119 void __init select_idle_routine(void) 120 { 121 /* 122 * If a platform has set its own idle routine, leave it alone. 123 */ 124 if (pm_idle) 125 return; 126 127 if (hlt_works()) 128 pm_idle = default_idle; 129 else 130 pm_idle = poll_idle; 131 } 132 133 static void do_nothing(void *unused) 134 { 135 } 136 137 void stop_this_cpu(void *unused) 138 { 139 local_irq_disable(); 140 set_cpu_online(smp_processor_id(), false); 141 142 for (;;) 143 cpu_sleep(); 144 } 145 146 /* 147 * cpu_idle_wait - Used to ensure that all the CPUs discard old value of 148 * pm_idle and update to new pm_idle value. Required while changing pm_idle 149 * handler on SMP systems. 150 * 151 * Caller must have changed pm_idle to the new value before the call. Old 152 * pm_idle value will not be used by any CPU after the return of this function. 153 */ 154 void cpu_idle_wait(void) 155 { 156 smp_mb(); 157 /* kick all the CPUs so that they exit out of pm_idle */ 158 smp_call_function(do_nothing, NULL, 1); 159 } 160 EXPORT_SYMBOL_GPL(cpu_idle_wait); 161