新版linux系统设备架构中关于电源管理方式的变更

新版linux系统设备架构中关于电源管理方式的变更
based on linux-2.6.32

一、设备模型各数据结构中电源管理的部分

linux的设备模型通过诸多结构体来联合描述，如struct device，struct device_type，struct class，
struct device_driver，struct bus_type等。

@kernel/include/linux/devices.h中有这几中结构体的定义，这里只列出和PM有关的项，其余查看源码：

struct device{
...
struct dev_pm_infopower;
...
}

struct device_type {
...
int (*uevent)(struct device *dev, struct kobj_uevent_env *env);
char *(*devnode)(struct device *dev, mode_t *mode);
void (*release)(struct device *dev);

const struct dev_pm_ops *pm;
};

struct class {
...
void (*class_release)(struct class *class);
void (*dev_release)(struct device *dev);

int (*suspend)(struct device *dev, pm_message_t state);
int (*resume)(struct device *dev);

const struct dev_pm_ops *pm;
...
};

struct device_driver {
...
int (*probe) (struct device *dev);
int (*remove) (struct device *dev);
void (*shutdown) (struct device *dev);
int (*suspend) (struct device *dev, pm_message_t state);
int (*resume) (struct device *dev);

const struct dev_pm_ops *pm;
...
};

struct bus_type {
...
int (*match)(struct device *dev, struct device_driver *drv);
int (*uevent)(struct device *dev, struct kobj_uevent_env *env);
int (*probe)(struct device *dev);
int (*remove)(struct device *dev);
void (*shutdown)(struct device *dev);

int (*suspend)(struct device *dev, pm_message_t state);
int (*resume)(struct device *dev);

const struct dev_pm_ops *pm;
...
};

以上可以看出和电源管理相关的两个结构体是struct dev_pm_info和struct dev_pm_ops，他们定义于文件
@kernel/include/linux/pm.h

struct dev_pm_info {
pm_message_tpower_state;
unsigned intcan_wakeup:1;
unsigned intshould_wakeup:1;
enum dpm_statestatus;/* Owned by the PM core - 表示该设备当前的PM状态*/
#ifdef CONFIG_PM_SLEEP
struct list_headentry;/* 链接到dpm_list全局链表中的连接体 */
#endif
#ifdef CONFIG_PM_RUNTIME// undef
struct timer_listsuspend_timer;
unsigned longtimer_expires;
struct work_structwork;
wait_queue_head_twait_queue;
spinlock_tlock;
atomic_tusage_count;
atomic_tchild_count;
unsigned intdisable_depth:3;
unsigned intignore_children:1;
unsigned intidle_notification:1;
unsigned intrequest_pending:1;
unsigned intdeferred_resume:1;
enum rpm_requestrequest;
enum rpm_statusruntime_status;
intruntime_error;
#endif
};

struct dev_pm_ops {
int (*prepare)(struct device *dev);
void (*complete)(struct device *dev);
int (*suspend)(struct device *dev);
int (*resume)(struct device *dev);
int (*freeze)(struct device *dev);
int (*thaw)(struct device *dev);
int (*poweroff)(struct device *dev);
int (*restore)(struct device *dev);
int (*suspend_noirq)(struct device *dev);
int (*resume_noirq)(struct device *dev);
int (*freeze_noirq)(struct device *dev);
int (*thaw_noirq)(struct device *dev);
int (*poweroff_noirq)(struct device *dev);
int (*restore_noirq)(struct device *dev);
int (*runtime_suspend)(struct device *dev);
int (*runtime_resume)(struct device *dev);
int (*runtime_idle)(struct device *dev);
};

二、device中的dev_pm_info结构体

device结构体中的power项用来将该设备纳入电源管理的范围，记录电源管理的一些信息。
在注册设备的时候调用函数device_add()来向sysfs系统添加power接口和注册进电源管理系统，代码片段如下：
...
error = dpm_sysfs_add(dev);@kernel/drivers/base/power/sysfs.c
if (error)
goto DPMError;
device_pm_add(dev);@kernel/drivers/base/power/main.c
...
其中dpm_sysfs_add()函数用来向sysfs文件系统中添加相应设备的power接口文件，如注册mt6516_tpd paltform device的时候，会在sysfs中出现如下目录和文件：
#pwd
/sys/devices/platform/mt6516-tpd
#cd mt6516-tpd
#ls -l
-rw-r--r-- root root 4096 2010-01-02 06:35 uevent
-r--r--r-- root root 4096 2010-01-02 06:39 modalias
lrwxrwxrwx root root 2010-01-02 06:39 subsystem -> ../../../bus/platform
drwxr-xr-x root root 2010-01-02 06:35 power
lrwxrwxrwx root root 2010-01-02 06:39 driver -> ../../../bus/platform/drivers/mt6516-tpd
#cd power
#ls -l
-rw-r--r-- root root 4096 2010-01-02 06:39 wakeup

源码片段：
static DEVICE_ATTR(wakeup, 0644, wake_show, wake_store);

static struct attribute * power_attrs[] = {
&dev_attr_wakeup.attr,
NULL,
};
static struct attribute_group pm_attr_group = {
.name= "power",// attribute_group结构体的name域不为NULL的话，都会已name建立一个属性目录的
.attrs= power_attrs,
};

int dpm_sysfs_add(struct device * dev)
{
return sysfs_create_group(&dev->kobj, &pm_attr_group);//在当前device的kobject结构体对应的目录下建立
}

其中的device_pm_add()函数会将该设备插入到电源管理的核心链表dpm_list中统一管理。
值得一提的是，在函数device_initialize()会调用函数device_pm_init()来初始化该device结构体的power域：
dev->power.status = DPM_ON;

void device_pm_add(struct device *dev)
{
...
mutex_lock(&dpm_list_mtx);
if (dev->parent) {
if (dev->parent->power.status >= DPM_SUSPENDING)
// 如果某设备处于DPM_SUSPENDING极其之后的状态，此时不允许以该设备为父设备注册子设备
dev_warn(dev, "parent %s should not be sleeping\n", dev_name(dev->parent));
} else if (transition_started) { // transition_started全局变量包含在PM transition期间不允许注册设备
/*
* We refuse to register parentless devices while a PM
* transition is in progress in order to avoid leaving them
* unhandled down the road
*/
dev_WARN(dev, "Parentless device registered during a PM transaction\n");
}

list_add_tail(&dev->power.entry, &dpm_list);// 将device结构体通过power.entry项链接进dpm_list
mutex_unlock(&dpm_list_mtx);
}

void device_pm_remove(struct device *dev)
{
...
mutex_lock(&dpm_list_mtx);
list_del_init(&dev->power.entry);
mutex_unlock(&dpm_list_mtx);
pm_runtime_remove(dev);
}

举例说明：

我们熟知的platform bus在系统中也是作为一种设备注册进了系统，在sysfs文件系统中的位置是：
/sys/devices/platform。使用函数device_register(&platform_bus)进行注册，调用device_add()函数，
注册ok之后，也会出现目录/sys/devices/platform/power。最后也会将其添加进dpm_list中。

i2c控制器外设代表的设备是注册在platform总线上的，也就是说它的父设备是platform。
最终在platform_device_add()中会调用函数device_add()函数来添加设备，最终也会在mt6516-i2c.0/
mt6516-i2c.1/mt6516-i2c.2中出现一个power目录，同时这3个platform设备会依靠
platform_device.dev.power.entry连接件链接到电源管理核心链表dpm_list中。
/sys/devices/platform/mt6516-i2c.2/power

每一个i2c控制器都会在系统中至少注册成一个适配器(adapter),该结构体将会间接提供给i2c设备的驱动来使用，以避免直接使用i2c控制器结构体。这个适配器没有对应的driver，在错综复杂的i2c架构中，相对于只起到了一个承上启下的作用，上接i2c控制器的结构体及driver，下接i2c设备的结构体i2c_client和特点的driver。adapter.dev.parent为i2c控制器对应的device，所以就会出现名为i2c-0/1/2的设备kobject，只是该设备的bus总线和device_type是：
adap->dev.bus = &i2c_bus_type;
adap->dev.type = &i2c_adapter_type;
然后调用函数device_register(&adap->dev);来注册这个device，所以在对应的i2c-0/1/2目录下也会出现power目录。
/sys/devices/platform/mt6516-i2c.2/i2c-2/power

i2c设备会通过自动检测或者事先静态描述的方式来注册进系统，不管什么方式，都会调用到函数：i2c_new_device()
struct i2c_client*client;
client->dev.parent = &client->adapter->dev;
client->dev.bus = &i2c_bus_type;
client->dev.type = &i2c_client_type;
dev_set_name(&client->dev, "%d-%04x", i2c_adapter_id(adap),
client->addr);
status = device_register(&client->dev);
可以看得出来名字是什么了，例如：2-00aa
#ls -l /sys/devices/platform/mt6516-i2c.2/i2c-2/2-00aa
-rw-r--r-- root root 4096 2010-01-02 06:35 uevent
-r--r--r-- root root 4096 2010-01-02 06:38 name
-r--r--r-- root root 4096 2010-01-02 06:38 modalias
lrwxrwxrwx root root 2010-01-02 06:38 subsystem -> ../../../../../bus/i2c
drwxr-xr-x root root 2010-01-02 06:35 power
lrwxrwxrwx root root 2010-01-02 06:38 driver -> ../../../../../bus/i2c/drivers/mt6516-tpd

三、bus_type、device_driver、device_type、class中的dev_pm_ops方法结构体
在新的linux内核中，已不再有subsystem数据结构了，他的功能被kset代替。

全局变量bus_kset初始化：kernel_init()-->do_basic_setup()-->driver_init()-->buses_init()
bus_kset = kset_create_and_add("bus", &bus_uevent_ops, NULL);

1. 总线类型结构体：bus_type，以platform和i2c总线为例：
@kernel/drivers/base/platform.c
static const struct dev_pm_ops platform_dev_pm_ops = {
.prepare = platform_pm_prepare,//
.complete = platform_pm_complete,//
.suspend = platform_pm_suspend,//
.resume = platform_pm_resume,//
.freeze = platform_pm_freeze,
.thaw = platform_pm_thaw,
.poweroff = platform_pm_poweroff,//
.restore = platform_pm_restore,
.suspend_noirq = platform_pm_suspend_noirq,
.resume_noirq = platform_pm_resume_noirq,
.freeze_noirq = platform_pm_freeze_noirq,
.thaw_noirq = platform_pm_thaw_noirq,
.poweroff_noirq = platform_pm_poweroff_noirq,
.restore_noirq = platform_pm_restore_noirq,
.runtime_suspend = platform_pm_runtime_suspend,
.runtime_resume = platform_pm_runtime_resume,
.runtime_idle = platform_pm_runtime_idle,
};

struct bus_type platform_bus_type = {
.name= "platform",
.dev_attrs= platform_dev_attrs,
.match= platform_match,
.uevent= platform_uevent,
.pm= &platform_dev_pm_ops,
};
从上面的dev_pm_ops结构体中拿出最普遍使用的函数指针来说明一下，对于bus_type它的电源管理是如何实现的。
static int platform_pm_prepare(struct device *dev)
{
struct device_driver *drv = dev->driver;
int ret = 0;

if (drv && drv->pm && drv->pm->prepare)
ret = drv->pm->prepare(dev);

return ret;
}
static void platform_pm_complete(struct device *dev)
{
struct device_driver *drv = dev->driver;

if (drv && drv->pm && drv->pm->complete)
drv->pm->complete(dev);
}
可以看出这两个函数都最终是利用了device_driver结构体中的dev_pm_ops函数方法结构体中的对应函数指针。

////////////////////////////////////////////
static int platform_legacy_suspend(struct device *dev, pm_message_t mesg)
{
struct platform_driver *pdrv = to_platform_driver(dev->driver);
struct platform_device *pdev = to_platform_device(dev);
int ret = 0;

if (dev->driver && pdrv->suspend)
ret = pdrv->suspend(pdev, mesg);

return ret;
}

static int platform_legacy_resume(struct device *dev)
{
struct platform_driver *pdrv = to_platform_driver(dev->driver);
struct platform_device *pdev = to_platform_device(dev);
int ret = 0;

if (dev->driver && pdrv->resume)
ret = pdrv->resume(pdev);

return ret;
}
////////////////////////////////////////////
static int platform_pm_suspend(struct device *dev)
{
struct device_driver *drv = dev->driver;
int ret = 0;

if (!drv)
return 0;

if (drv->pm) {
if (drv->pm->suspend)
ret = drv->pm->suspend(dev);
} else {
ret = platform_legacy_suspend(dev, PMSG_SUSPEND);
}

return ret;
}

static int platform_pm_resume(struct device *dev)
{
struct device_driver *drv = dev->driver;
int ret = 0;

if (!drv)
return 0;

if (drv->pm) {
if (drv->pm->resume)
ret = drv->pm->resume(dev);
} else {
ret = platform_legacy_resume(dev);
}

return ret;
}

这里suspend和resume函数也是最终都是调用了device_driver结构体的dev_pm_ops方法结构体中的对应函数指针(device_driver.pm项被初始化)，否则使用老式的方法：platform_legacy_suspend(dev, PMSG_SUSPEND)和platform_legacy_resume(dev)。根据这两个函数的源码可以看出。一般地，在我们的platform device的platform driver定义中，都是实现了pdrv.suspend和pdrv.resume函数，而并没有实现pdrv.driver.suspend和pdrv.driver.resume函数，其余三个函数可以在platform_driver_register()函数中看出：
int platform_driver_register(struct platform_driver *drv)
{
drv->driver.bus = &platform_bus_type;
if (drv->probe)
drv->driver.probe = platform_drv_probe;
if (drv->remove)
drv->driver.remove = platform_drv_remove;
if (drv->shutdown)
drv->driver.shutdown = platform_drv_shutdown;

return driver_register(&drv->driver);
}

i2c总线注册没有使用新式的电源管理方法：dev_pm_ops，仍然使用老式的方式：
@kernel/drivers/i2c/i2c-core.c
struct bus_type i2c_bus_type = {
.name= "i2c",
.match= i2c_device_match,
.probe= i2c_device_probe,
.remove= i2c_device_remove,
.shutdown= i2c_device_shutdown,
.suspend= i2c_device_suspend,
.resume= i2c_device_resume,
};

static int i2c_device_suspend(struct device *dev, pm_message_t mesg)
{
struct i2c_client *client = i2c_verify_client(dev);
struct i2c_driver *driver;

if (!client || !dev->driver)
return 0;
driver = to_i2c_driver(dev->driver);
if (!driver->suspend)
return 0;
return driver->suspend(client, mesg);
}

static int i2c_device_resume(struct device *dev)
{
struct i2c_client *client = i2c_verify_client(dev);
struct i2c_driver *driver;

if (!client || !dev->driver)
return 0;
driver = to_i2c_driver(dev->driver);
if (!driver->resume)
return 0;
return driver->resume(client);
}
// 实际上都是调用的i2c_driver结构体的suspend和resume函数。

2. device_type结构体暂时还没有找到有哪一个模块使用了新式了dev_pm_ops电源管理方法，一般都是没有实现这部分。

3. class结构体也没有找到使用dev_pm_ops方法结构体的地方，先暂时放一放。

4. device_driver
struct device_driver {
const char*name;
struct bus_type*bus;
...
int (*probe) (struct device *dev);
int (*remove) (struct device *dev);
void (*shutdown) (struct device *dev);
int (*suspend) (struct device *dev, pm_message_t state);
int (*resume) (struct device *dev);
const struct attribute_group **groups;

const struct dev_pm_ops *pm;

struct driver_private *p;
};

struct i2c_driver {
...
/* driver model interfaces that don't relate to enumeration */
void (*shutdown)(struct i2c_client *);
int (*suspend)(struct i2c_client *, pm_message_t mesg);
int (*resume)(struct i2c_client *);
...
struct device_driver driver;
const struct i2c_device_id *id_table;

/* Device detection callback for automatic device creation */
int (*detect)(struct i2c_client *, int kind, struct i2c_board_info *);
const struct i2c_client_address_data *address_data;
struct list_head clients;
};
一般都是实现了platform driver和i2c_driver结构体的suspend和resume函数,并没有使用新式的电源管理方式。