设备初始化流程：
device_register(dev)->device_initialize(dev)->device_pm_init(dev)->INIT_LIST_HEAD(&dev->power.entry);
设备添加流程：
device_add(dev)->device_pm_add(dev)->list_add_tail(&dev->power.entry,&dpm_list);
从设备初始化和添加到设备模型的流程可以看出，每个设备在注册和添加的过程中对应的device->power.entry被添加到了dpm_list链表中。
devicesuspend由suspend模块完成，suspend模块由CONFIG_SUSPEND宏开关控制
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- obj-$(CONFIG_SUSPEND) += suspend.o
代码就在kernel/power/suspend.c中
suspend模块对外导出了pm_suspend接口：
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-
- int pm_suspend(suspend_state_t state)
- {
- int error;
-
- if (state <= PM_SUSPEND_ON || state >= PM_SUSPEND_MAX)
- return -EINVAL;
-
- error = enter_state(state);
- if (error) {
- suspend_stats.fail++;
- dpm_save_failed_errno(error);
- } else {
- suspend_stats.success++;
- }
- return error;
- }
- EXPORT_SYMBOL(pm_suspend);
pm_suspend被用来控制系统的设备进入指定的状态。前面提到的Linux定义的四种电源状态会被传递到这个函数，pm_suspend会对电源状态做检查，如果传入的是非法之，直接返回EINVAL。
四种电源状态定在include/linux/suspend.h文件中
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- typedef int __bitwise suspend_state_t;
-
- #define PM_SUSPEND_ON ((__force suspend_state_t) 0)
- #define PM_SUSPEND_STANDBY ((__force suspend_state_t) 1)
- #define PM_SUSPEND_MEM ((__force suspend_state_t) 3)
- #define PM_SUSPEND_MAX ((__force suspend_state_t) 4)
针对具体设备休眠的操作都在针对设备休眠的驱动里面。相关的文件在driver/base/power/目录下。针对设备的休眠动作在driver/base/power/main.c文件中。该文件对外导出了三个接口，suspend模块用到了这些接口。
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-
- int dpm_suspend_start(pm_message_t state)
- {
- int error;
-
- error = dpm_prepare(state);
- if (error) {
- suspend_stats.failed_prepare++;
- dpm_save_failed_step(SUSPEND_PREPARE);
- } else
- error = dpm_suspend(state);
- return error;
- }
- EXPORT_SYMBOL_GPL(dpm_suspend_start);
-
- void __suspend_report_result(const char *function, void *fn, int ret)
- {
- if (ret)
- printk(KERN_ERR "%s(): %pF returns %d\n", function, fn, ret);
- }
- EXPORT_SYMBOL_GPL(__suspend_report_result);
-
-
- int device_pm_wait_for_dev(struct device *subordinate, struct device *dev)
- {
- dpm_wait(dev, subordinate->power.async_suspend);
- return async_error;
- }
- EXPORT_SYMBOL_GPL(device_pm_wait_for_dev);
3.3平台相关挂起操作(platform suspending)在设备挂起操作完成之后，会针对特定平台做状态转换操作。Linux内核电源管理模块也为此定义了一组标准函数接口。不同架构只需要实现相应接口即可。
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- struct platform_suspend_ops {
- int (*valid)(suspend_state_t state);
- int (*begin)(suspend_state_t state);
- int (*prepare)(void);
- int (*prepare_late)(void);
- int (*enter)(suspend_state_t state);
- void (*wake)(void);
- void (*finish)(void);
- bool (*suspend_again)(void);
- void (*end)(void);
- void (*recover)(void);
- };
这组函数功能如下：
structplatform_suspend_ops定义了一组用于管理不同平台的下系统进入休眠状态的回调函数。这部分跟MCU关系非常紧密，涉及到时钟，PLL，电压域，频率，总线等系统级的物理模块进入休眠状态。每个具体的函数功能，在sourcecode中有详细的注释。 |
