drivers/cpuidle/driver.c

   1 /*
   2  * driver.c - driver support
   3  *
   4  * (C) 2006-2007 Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
   5  *               Shaohua Li <shaohua.li@intel.com>
   6  *               Adam Belay <abelay@novell.com>
   7  *
   8  * This code is licenced under the GPL.
   9  */
  10
  11 #include <linux/mutex.h>
  12 #include <linux/module.h>
  13 #include <linux/cpuidle.h>
  14
  15 #include "cpuidle.h"
  16
  17 static struct cpuidle_driver *cpuidle_curr_driver;
  18 DEFINE_SPINLOCK(cpuidle_driver_lock);
  19
  20 static void __cpuidle_register_driver(struct cpuidle_driver *drv)
  21 {
  22         int i;
  23         /*
  24          * cpuidle driver should set the drv->power_specified bit
  25          * before registering if the driver provides
  26          * power_usage numbers.
  27          *
  28          * If power_specified is not set,
  29          * we fill in power_usage with decreasing values as the
  30          * cpuidle code has an implicit assumption that state Cn
  31          * uses less power than C(n-1).
  32          *
  33          * With CONFIG_ARCH_HAS_CPU_RELAX, C0 is already assigned
  34          * an power value of -1.  So we use -2, -3, etc, for other
  35          * c-states.
  36          */
  37         if (!drv->power_specified) {
  38                 for (i = CPUIDLE_DRIVER_STATE_START; i < drv->state_count; i++)
  39                         drv->states[i].power_usage = -1 - i;
  40         }
  41 }
  42
  43
  44 /**
  45  * cpuidle_register_driver - registers a driver
  46  * @drv: the driver
  47  */
  48 int cpuidle_register_driver(struct cpuidle_driver *drv)
  49 {
  50         if (!drv || !drv->state_count)
  51                 return -EINVAL;
  52
  53         if (cpuidle_disabled())
  54                 return -ENODEV;
  55
  56         spin_lock(&cpuidle_driver_lock);
  57         if (cpuidle_curr_driver) {
  58                 spin_unlock(&cpuidle_driver_lock);
  59                 return -EBUSY;
  60         }
  61         __cpuidle_register_driver(drv);
  62         cpuidle_curr_driver = drv;
  63         spin_unlock(&cpuidle_driver_lock);
  64
  65         return 0;
  66 }
  67
  68 EXPORT_SYMBOL_GPL(cpuidle_register_driver);
  69
  70 /**
  71  * cpuidle_get_driver - return the current driver
  72  */
  73 struct cpuidle_driver *cpuidle_get_driver(void)
  74 {
  75         return cpuidle_curr_driver;
  76 }
  77 EXPORT_SYMBOL_GPL(cpuidle_get_driver);
  78
  79 /**
  80  * cpuidle_unregister_driver - unregisters a driver
  81  * @drv: the driver
  82  */
  83 void cpuidle_unregister_driver(struct cpuidle_driver *drv)
  84 {
  85         if (drv != cpuidle_curr_driver) {
  86                 WARN(1, "invalid cpuidle_unregister_driver(%s)\n",
  87                         drv->name);
  88                 return;
  89         }
  90
  91         spin_lock(&cpuidle_driver_lock);
  92         cpuidle_curr_driver = NULL;
  93         spin_unlock(&cpuidle_driver_lock);
  94 }
  95
  96 EXPORT_SYMBOL_GPL(cpuidle_unregister_driver);