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 23 static int hlt_counter; 24 void (*pm_idle)(void) = NULL; 25 void (*pm_power_off)(void); 26 EXPORT_SYMBOL(pm_power_off); 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 if (!need_resched()) { 66 local_irq_enable(); 67 cpu_sleep(); 68 } else 69 local_irq_enable(); 70 71 set_thread_flag(TIF_POLLING_NRFLAG); 72 } else 73 poll_idle(); 74 } 75 76 /* 77 * The idle thread. There's no useful work to be done, so just try to conserve 78 * power and have a low exit latency (ie sit in a loop waiting for somebody to 79 * say that they'd like to reschedule) 80 */ 81 void cpu_idle(void) 82 { 83 unsigned int cpu = smp_processor_id(); 84 85 set_thread_flag(TIF_POLLING_NRFLAG); 86 87 /* endless idle loop with no priority at all */ 88 while (1) { 89 tick_nohz_stop_sched_tick(1); 90 91 while (!need_resched() && cpu_online(cpu)) { 92 check_pgt_cache(); 93 rmb(); 94 95 local_irq_disable(); 96 /* Don't trace irqs off for idle */ 97 stop_critical_timings(); 98 pm_idle(); 99 /* 100 * Sanity check to ensure that pm_idle() returns 101 * with IRQs enabled 102 */ 103 WARN_ON(irqs_disabled()); 104 start_critical_timings(); 105 } 106 107 tick_nohz_restart_sched_tick(); 108 preempt_enable_no_resched(); 109 schedule(); 110 preempt_disable(); 111 } 112 } 113 114 void __cpuinit select_idle_routine(void) 115 { 116 /* 117 * If a platform has set its own idle routine, leave it alone. 118 */ 119 if (pm_idle) 120 return; 121 122 if (hlt_works()) 123 pm_idle = default_idle; 124 else 125 pm_idle = poll_idle; 126 } 127 128 static void do_nothing(void *unused) 129 { 130 } 131 132 /* 133 * cpu_idle_wait - Used to ensure that all the CPUs discard old value of 134 * pm_idle and update to new pm_idle value. Required while changing pm_idle 135 * handler on SMP systems. 136 * 137 * Caller must have changed pm_idle to the new value before the call. Old 138 * pm_idle value will not be used by any CPU after the return of this function. 139 */ 140 void cpu_idle_wait(void) 141 { 142 smp_mb(); 143 /* kick all the CPUs so that they exit out of pm_idle */ 144 smp_call_function(do_nothing, NULL, 1); 145 } 146 EXPORT_SYMBOL_GPL(cpu_idle_wait); 147