ACPI包括很多功能，电源管理是其功能之一，具体的ACPI的介绍可以参考ACPI的技术文档。

Linux中利用模块机制，实现ACPI对电源的管理：

static struct cpufreq_driver acpi_cpufreq_driver = {

.verify= acpi_cpufreq_verify,

.target= acpi_cpufreq_target,

.bios_limit= acpi_processor_get_bios_limit,

.init= acpi_cpufreq_cpu_init,

.exit= acpi_cpufreq_cpu_exit,

.resume= acpi_cpufreq_resume,

.name= "acpi-cpufreq",

.owner= THIS_MODULE,

.attr= acpi_cpufreq_attr,

};

模块的初始化工作由以下代码完成：

static int __init acpi_cpufreq_init(void)

{

int ret;

if (acpi_disabled)

return 0;

pr_debug("acpi_cpufreq_init\n");

ret = acpi_cpufreq_early_init();

if (ret)

return ret;

ret = cpufreq_register_driver(&acpi_cpufreq_driver);//核心

if (ret)

free_acpi_perf_data();

return ret;

}

主要是cpufreq_register_driver：

/*********************************************************************

* REGISTER / UNREGISTER CPUFREQ DRIVER *

*********************************************************************/

/**

* cpufreq_register_driver - register a CPU Frequency driver

* @driver_data: A struct cpufreq_driver containing the values#

* submitted by the CPU Frequency driver.

*

* Registers a CPU Frequency driver to this core code. This code

* returns zero on success, -EBUSY when another driver got here first

* (and isn't unregistered in the meantime).

*

*/

int cpufreq_register_driver(struct cpufreq_driver *driver_data)

{

unsigned long flags;

int ret;

if (!driver_data || !driver_data->verify || !driver_data->init ||

((!driver_data->setpolicy) && (!driver_data->target)))

return -EINVAL;

pr_debug("trying to register driver %s\n", driver_data->name);

if (driver_data->setpolicy)

driver_data->flags |= CPUFREQ_CONST_LOOPS;

spin_lock_irqsave(&cpufreq_driver_lock, flags);

if (cpufreq_driver) {

spin_unlock_irqrestore(&cpufreq_driver_lock, flags);

return -EBUSY;

}

cpufreq_driver = driver_data;

spin_unlock_irqrestore(&cpufreq_driver_lock, flags);

ret = sysdev_driver_register(&cpu_sysdev_class,

&cpufreq_sysdev_driver);

if (ret)

goto err_null_driver;

if (!(cpufreq_driver->flags & CPUFREQ_STICKY)) {

int i;

ret = -ENODEV;

/* check for at least one working CPU */

for (i = 0; i < nr_cpu_ids; i++)

if (cpu_possible(i) && per_cpu(cpufreq_cpu_data, i)) {

ret = 0;

break;

}

/* if all ->init() calls failed, unregister */

if (ret) {

pr_debug("no CPU initialized for driver %s\n",

driver_data->name);

goto err_sysdev_unreg;

}

}

register_hotcpu_notifier(&cpufreq_cpu_notifier);

pr_debug("driver %s up and running\n", driver_data->name);

return 0;

err_sysdev_unreg:

sysdev_driver_unregister(&cpu_sysdev_class,

&cpufreq_sysdev_driver);

err_null_driver:

spin_lock_irqsave(&cpufreq_driver_lock, flags);

cpufreq_driver = NULL;

spin_unlock_irqrestore(&cpufreq_driver_lock, flags);

return ret;

}

为什么不直接引用acpi_cpufreq_driver呢？

由于传递过来的参数是acpi_cpufreq_driver，因此以后引用cpufreq_driver就相当于引用acpi_cpufreq_driver了。为什么这么做呢？因为，还有一种叫做pcc_cpufreq_driver的东西，和acpi_cpufreq_driver一样，是电源管理的一种方式，它的初始化也是用这个函数，因为这两种方式你只能选择一种，因此，cpufreq_driver要么是acpi_cpufreq_driver，要么是pcc_cpufreq_driver。这样的实现方式，避免了代码的重复！

有这样一行代码

cpufreq_driver = driver_data;