arch/powerpc/kernel/idle.c

   1 /*
   2  * Idle daemon for PowerPC.  Idle daemon will handle any action
   3  * that needs to be taken when the system becomes idle.
   4  *
   5  * Originally written by Cort Dougan (cort@cs.nmt.edu).
   6  * Subsequent 32-bit hacking by Tom Rini, Armin Kuster,
   7  * Paul Mackerras and others.
   8  *
   9  * iSeries supported added by Mike Corrigan <mikejc@us.ibm.com>
  10  *
  11  * Additional shared processor, SMT, and firmware support
  12  *    Copyright (c) 2003 Dave Engebretsen <engebret@us.ibm.com>
  13  *
  14  * 32-bit and 64-bit versions merged by Paul Mackerras <paulus@samba.org>
  15  *
  16  * This program is free software; you can redistribute it and/or
  17  * modify it under the terms of the GNU General Public License
  18  * as published by the Free Software Foundation; either version
  19  * 2 of the License, or (at your option) any later version.
  20  */
  21
  22 #include <linux/sched.h>
  23 #include <linux/kernel.h>
  24 #include <linux/smp.h>
  25 #include <linux/cpu.h>
  26 #include <linux/sysctl.h>
  27 #include <linux/tick.h>
  28
  29 #include <asm/system.h>
  30 #include <asm/processor.h>
  31 #include <asm/cputable.h>
  32 #include <asm/time.h>
  33 #include <asm/machdep.h>
  34 #include <asm/smp.h>
  35
  36 #ifdef CONFIG_HOTPLUG_CPU
  37 #define cpu_should_die()        cpu_is_offline(smp_processor_id())
  38 #else
  39 #define cpu_should_die()        0
  40 #endif
  41
  42 static int __init powersave_off(char *arg)
  43 {
  44         ppc_md.power_save = NULL;
  45         return 0;
  46 }
  47 __setup("powersave=off", powersave_off);
  48
  49 #if defined(CONFIG_PPC_PSERIES) && defined(CONFIG_TRACEPOINTS)
  50 static const bool idle_uses_rcu = 1;
  51 #else
  52 static const bool idle_uses_rcu;
  53 #endif
  54
  55 /*
  56  * The body of the idle task.
  57  */
  58 void cpu_idle(void)
  59 {
  60         if (ppc_md.idle_loop)
  61                 ppc_md.idle_loop();     /* doesn't return */
  62
  63         set_thread_flag(TIF_POLLING_NRFLAG);
  64         while (1) {
  65                 if (idle_uses_rcu)
  66                         tick_nohz_idle_enter();
  67                 else
  68                         tick_nohz_idle_enter_norcu();
  69                 while (!need_resched() && !cpu_should_die()) {
  70                         ppc64_runlatch_off();
  71
  72                         if (ppc_md.power_save) {
  73                                 clear_thread_flag(TIF_POLLING_NRFLAG);
  74                                 /*
  75                                  * smp_mb is so clearing of TIF_POLLING_NRFLAG
  76                                  * is ordered w.r.t. need_resched() test.
  77                                  */
  78                                 smp_mb();
  79                                 local_irq_disable();
  80
  81                                 /* Don't trace irqs off for idle */
  82                                 stop_critical_timings();
  83
  84                                 /* check again after disabling irqs */
  85                                 if (!need_resched() && !cpu_should_die())
  86                                         ppc_md.power_save();
  87
  88                                 start_critical_timings();
  89
  90                                 local_irq_enable();
  91                                 set_thread_flag(TIF_POLLING_NRFLAG);
  92
  93                         } else {
  94                                 /*
  95                                  * Go into low thread priority and possibly
  96                                  * low power mode.
  97                                  */
  98                                 HMT_low();
  99                                 HMT_very_low();
 100                         }
 101                 }
 102
 103                 HMT_medium();
 104                 ppc64_runlatch_on();
 105                 if (idle_uses_rcu)
 106                         tick_nohz_idle_exit();
 107                 else
 108                         tick_nohz_idle_exit_norcu();
 109                 preempt_enable_no_resched();
 110                 if (cpu_should_die())
 111                         cpu_die();
 112                 schedule();
 113                 preempt_disable();
 114         }
 115 }
 116
 117 int powersave_nap;
 118
 119 #ifdef CONFIG_SYSCTL
 120 /*
 121  * Register the sysctl to set/clear powersave_nap.
 122  */
 123 static ctl_table powersave_nap_ctl_table[]={
 124         {
 125                 .procname       = "powersave-nap",
 126                 .data           = &powersave_nap,
 127                 .maxlen         = sizeof(int),
 128                 .mode           = 0644,
 129                 .proc_handler   = proc_dointvec,
 130         },
 131         {}
 132 };
 133 static ctl_table powersave_nap_sysctl_root[] = {
 134         {
 135                 .procname       = "kernel",
 136                 .mode           = 0555,
 137                 .child          = powersave_nap_ctl_table,
 138         },
 139         {}
 140 };
 141
 142 static int __init
 143 register_powersave_nap_sysctl(void)
 144 {
 145         register_sysctl_table(powersave_nap_sysctl_root);
 146
 147         return 0;
 148 }
 149 __initcall(register_powersave_nap_sysctl);
 150 #endif