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Linux电源管理(7)_Wakeup events framework_wfi wakeup events

wfi wakeup events

1. 前言

本文继续“Linux电源管理(6)_Generic PM之Suspend功能”中有关suspend同步以及PM wakeup的话题。这个话题,是近几年Linux kernel最具争议的话题之一,在国外Linux开发论坛,经常可以看到围绕该话题的辩论。辩论的时间跨度和空间跨度可以持续很长,且无法达成一致。

wakeup events framework是这个话题的一个临时性的解决方案,包括wake lock、wakeup count、autosleep等机制。它们就是本文的话题。

2. wakeup events framework要解决的问题

我们知道,系统处于suspend状态,可通过wakeup events唤醒。具体的wakeup events可以是按键按下,可以是充电器插入,等等。但是,如果在suspend的过程中,产生了wakeup events,怎么办?答案很肯定,"wakeup"系统。由于此时系统没有真正suspend,所以这的"wakeup"是个假动作,实际上只是终止suspend。

但由于系统在suspend的过程中,会进行process freeze、 device suspend等操作,而这些操作可能导致内核或用户空间程序不能及时获取wakeup events,从而使系统不能正确wakeup,这就是wakeup events framework要解决的问题:system suspend和system wakeup events之间的同步问题。

3. wakeup events framework的功能总结

仔细推敲一下,上面所讲的同步问题包括两种情况:

情况1:内核空间的同步

wakeup events产生后,通常是以中断的形式通知device driver。driver会处理events,处理的过程中,系统不能suspend。

注1:同步问题只存在于中断开启的情况,因为若中断关闭,就不会产生wakeup events,也就不存在同步的概念。

情况2:用户空间的同步

一般情况下,driver对wakeup events处理后,会交给用户空间程序继续处理,处理的过程,也不允许suspend。这又可以分为两种情况:

1)进行后续处理的用户进程,根本没有机会被调度,即该wakeup events无法上报到用户空间。

2)进行后续处理的用户进程被调度,处理的过程中(以及处理结束后,决定终止suspend操作),系统不能suspend。

因此,wakeup events framework就包括3大功能:

解决内核空间同步问题(framework的核心功能);

解决用户空间同步问题的情景1(wakeup count功能);

解决用户空间同步问题的情景2(wake lock功能) 。

注2:
用户空间同步的两种情况,咋一看,非常合乎情理,kernel你得好好处理!但事实上,该同步问题牵涉到了另外一个比较有争议的话题:日常的电源管理机制。是否要基于suspend实现?系统何时进入低功耗状态,应该由谁决定?kernel还是用户空间程序?

这最终会决定是否存在用空间同步问题。但是,在当前这个时间点,对这个话题,Linux kernel developers和Android developers持相反的观点。这也造成了wakeup events framework在实现上的撕裂。Kernel的本意是不愿处理用户空间同步问题的,但为了兼容Android平台,不得不增加相关的功能(Wakeup count和Wake lock)。

蜗蜗会在下一篇文章和大家探讨该话题,本文就先focus在wakeup events framework上。

4. wakeup events framework architecture

下面图片描述了wakeup events framework的architecture:

image

图片中红色边框的block是wakeup events相关的block:

抽象wakeup source和wakeup event的概念;

向各个device driver提供wakeup source的注册、使能等接口;

向各个device driver提供wakeup event的上报、停止等接口;

向上层的PM core(包括wakeup count、auto sleep、suspend、hibernate等模块)提供wakeup event的查询接口,以判断是否可以suspend、是否需要终止正在进行的suspend。

2)wakeup events framework sysfs,将设备的wakeup信息,以sysfs的形式提供到用户空间,供用户空间程序查询、配置。在drivers/base/power/sysfs.c中实现。

3)wake lock/unlock,为了兼容Android旧的wakeup lock机制而留下的一个后门,扩展wakeup events framework的功能,允许用户空间程序报告/停止wakeup events。换句话说,该后门允许用户空间的任一程序决定系统是否可以休眠。

4)wakeup count,基于wakeup events framework,解决用户空间同步的问题。

5)auto sleep,允许系统在没有活动时(即一段时间内,没有产生wakeup event),自动休眠。

注3:在Linux kernel看来,power是系统的核心资源,不应开放给用户程序随意访问(wake lock机制违背了这个原则)。而在运行时的电源管理过程中,系统何时进入低功耗状态,也不是用户空间程序能决定的(auto sleep中枪了)。因此,kernel对上述功能的支持,非常的不乐意,我们可以从kernel/power/main.c中sysfs attribute文件窥见一斑(只要定义了PM_SLEEP,就一定支持wakeup count功能,但autosleep和wake lock功能,由另外的宏定义控制):

  1. 1: static struct attribute * g[] = {
  2. 2: &state_attr.attr,
  3. 3: #ifdef CONFIG_PM_TRACE
  4. 4: &pm_trace_attr.attr,
  5. 5: &pm_trace_dev_match_attr.attr,
  6. 6: #endif
  7. 7: #ifdef CONFIG_PM_SLEEP
  8. 8: &pm_async_attr.attr,
  9. 9: &wakeup_count_attr.attr,
  10. 10: #ifdef CONFIG_PM_AUTOSLEEP
  11. 11: &autosleep_attr.attr,
  12. 12: #endif
  13. 13: #ifdef CONFIG_PM_WAKELOCKS
  14. 14: &wake_lock_attr.attr,
  15. 15: &wake_unlock_attr.attr,
  16. 16: #endif
  17. 17: #ifdef CONFIG_PM_DEBUG
  18. 18: &pm_test_attr.attr,
  19. 19: #endif
  20. 20: #ifdef CONFIG_PM_SLEEP_DEBUG
  21. 21: &pm_print_times_attr.attr,
  22. 22: #endif
  23. 23: #endif
  24. 24: #ifdef CONFIG_FREEZER
  25. 25: &pm_freeze_timeout_attr.attr,
  26. 26: #endif
  27. 27: NULL,
  28. 28: };

5. 代码分析

5.1 wakeup source和wakeup event

在kernel中,可以唤醒系统的只有设备(struct device),但并不是每个设备都具备唤醒功能,那些具有唤醒功能的设备称作wakeup source。是时候回到这篇文章中了(Linux设备模型(5)_device和device driver),在那里,介绍struct device结构时,涉及到一个struct dev_pm_info类型的power变量,蜗蜗说留待后面的专题讲解。我们再回忆一下struct device结构:

  1. 1: struct device {
  2. 2: ...
  3. 3: struct dev_pm_info power;
  4. 4: ...
  5. 5: };

该结构中有一个power变量,保存了和wakeup event相关的信息,让我们接着看一下struct dev_pm_info数据结构(只保留和本文有关的内容):

  1. 1: struct dev_pm_info {
  2. 2: ...
  3. 3: unsigned int can_wakeup:1;
  4. 4: ...
  5. 5: #ifdef CONFIG_PM_SLEEP
  6. 6: ...
  7. 7: struct wakeup_source *wakeup;
  8. 8: ...
  9. 9: #else
  10. 10: unsigned int should_wakeup:1;
  11. 11: #endif
  12. 12: };

can_wakeup,标识本设备是否具有唤醒能力。只有具备唤醒能力的设备,才会在sysfs中有一个power目录,用于提供所有的wakeup信息,这些信息是以struct wakeup_source的形式组织起来的。也就是上面wakeup指针。具体有哪些信息呢?让我们看看struct wakeup_source的定义。

  1. 1: /* include\linux\pm_wakeup.h */
  2. 2: struct wakeup_source {
  3. 3: const char *name;
  4. 4: struct list_head entry;
  5. 5: spinlock_t lock;
  6. 6: struct timer_list timer;
  7. 7: unsigned long timer_expires;
  8. 8: ktime_t total_time;
  9. 9: ktime_t max_time;
  10. 10: ktime_t last_time;
  11. 11: ktime_t start_prevent_time;
  12. 12: ktime_t prevent_sleep_time;
  13. 13: unsigned long event_count;
  14. 14: unsigned long active_count;
  15. 15: unsigned long relax_count;
  16. 16: unsigned long expire_count;
  17. 17: unsigned long wakeup_count;
  18. 18: bool active:1;
  19. 19: bool autosleep_enabled:1;
  20. 20: };

因此,一个wakeup source代表了一个具有唤醒能力的设备,也称该设备为一个wakeup source。该结构中各个字段的意义如下:

name,该wakeup source的名称,一般为对应的device name(有个例外,就是wakelock);

entery,用于将所有的wakeup source挂在一个链表中;

timer、timer_expires,一个wakeup source产生了wakeup event,称作wakeup source activate,wakeup event处理完毕后(不再需要系统为此保持active),称作deactivate。activate和deactivate的操作可以由driver亲自设置,也可以在activate时,指定一个timeout时间,时间到达后,由wakeup events framework自动将其设置为deactivate状态。这里的timer以及expires时间,就是用来实现该功能;

total_time,该wakeup source处于activate状态的总时间(可以指示该wakeup source对应的设备的繁忙程度、耗电等级);

max_time,该wakeup source持续处于activate状态的最大时间(越长越不合理);

last_time,该wakeup source上次active的开始时间;

start_prevent_time,该wakeup source开始阻止系统自动睡眠(auto sleep)的时间点;

prevent_sleep_time,该wakeup source阻止系统自动睡眠的总时间;

event_count,wakeup source上报的event个数;

active_count,wakeup source activate的次数;

relax_count, wakeup source deactivate的次数;

expire_count,wakeup source timeout到达的次数;

wakeup_count,wakeup source终止suspend过程的次数;

active,wakeup source的activate状态;

autosleep_enabled,记录系统auto sleep的使能状态(每个wakeup source都重复记录这样一个状态,这种设计真实不敢恭维!)

wakeup source代表一个具有唤醒能力的设备,该设备产生的可以唤醒系统的事件,就称作wakeup event。当wakeup source产生wakeup event时,需要将wakeup source切换为activate状态;当wakeup event处理完毕后,要切换为deactivate状态。因此,我们再来理解一下几个wakeup source比较混淆的变量:event_count, active_count和wakeup_count:

event_count,wakeup source产生的wakeup event的个数;

active_count,产生wakeup event时,wakeup source需要切换到activate状态。但并不是每次都要切换,因此有可能已经处于activate状态了。因此active_count可能小于event_count,换句话说,很有可能在前一个wakeup event没被处理完时,又产生了一个。这从一定程度上反映了wakeup source所代表的设备的繁忙程度;

wakeup_count,wakeup source在suspend过程中产生wakeup event的话,就会终止suspend过程,该变量记录了wakeup source终止suspend过程的次数(如果发现系统总是suspend失败,检查一下各个wakeup source的该变量,就可以知道问题出在谁身上了)。

5.2 几个counters

在drivers\base\power\wakeup.c中,有几个比较重要的计数器,是wakeup events framework的实现基础,包括:

1)registered wakeup events和saved_count

记录了系统运行以来产生的所有wakeup event的个数,在wakeup source上报event时加1。

这个counter对解决用户空间同步问题很有帮助,因为一般情况下(无论是用户程序主动suspend,还是auto sleep),由专门的进程(或线程)触发suspend。当这个进程判断系统满足suspend条件,决定suspend时,会记录一个counter值(saved_count)。在后面suspend的过程中,如果系统发现counter有变,则说明系统产生了新的wakeup event,这样就可以终止suspend。

该功能即是wakeup count功能,会在后面更详细的说明。

2)wakeup events in progress

记录正在处理的event个数。

当wakeup source产生wakeup event时,会通过wakeup events framework提供的接口将wakeup source设置为activate状态。当该event处理结束后,设置为deactivate状态。activate到deactivate的区间,表示该event正在被处理。

当系统中有任何正在被处理的wakeup event时,则不允许suspend。如果suspend正在进行,则要终止。

思考一个问题:registered wakeup events在什么时候增加?答案是在wakeup events in progress减小时,因为已经完整的处理完一个event了,可以记录在案了。

  1. 1: /*
  2. 2: * Combined counters of registered wakeup events and wakeup events in progress.
  3. 3: * They need to be modified together atomically, so it's better to use one
  4. 4: * atomic variable to hold them both.
  5. 5: */
  6. 6: static atomic_t combined_event_count = ATOMIC_INIT(0);
  7. 7:
  8. 8: #define IN_PROGRESS_BITS (sizeof(int) * 4)
  9. 9: #define MAX_IN_PROGRESS ((1 << IN_PROGRESS_BITS) - 1)
  10. 10:
  11. 11: static void split_counters(unsigned int *cnt, unsigned int *inpr)
  12. 12: {
  13. 13: unsigned int comb = atomic_read(&combined_event_count);
  14. 14:
  15. 15: *cnt = (comb >> IN_PROGRESS_BITS);
  16. 16: *inpr = comb & MAX_IN_PROGRESS;
  17. 17: }

定义和读取。

   1: cec = atomic_add_return(MAX_IN_PROGRESS, &combined_event_count);

wakeup events in progress减1,registered wakeup events加1,这个语句简直是美轮美奂,读者可以仔细品味一下,绝对比看xxx片还过瘾,哈哈。

   1: cec = atomic_inc_return(&combined_event_count);

wakeup events in progress加1。

5.3 wakeup events framework的核心功能

wakeup events framework的核心功能体现在它向底层的设备驱动所提供的用于上报wakeup event的接口,这些接口根据操作对象可分为两类,具体如下。

类型一(操作对象为wakeup source,编写设备驱动时,一般不会直接使用):

  1. 1: /* include/linux/pm_wakeup.h */
  2. 2: extern void __pm_stay_awake(struct wakeup_source *ws);
  3. 3: extern void __pm_relax(struct wakeup_source *ws);
  4. 4: extern void __pm_wakeup_event(struct wakeup_source *ws, unsigned int msec);

__pm_stay_awake,通知PM core,ws产生了wakeup event,且正在处理,因此不允许系统suspend(stay awake);

__pm_relax,通知PM core,ws没有正在处理的wakeup event,允许系统suspend(relax);

__pm_wakeup_event,为上边两个接口的功能组合,通知PM core,ws产生了wakeup event,会在msec毫秒内处理结束(wakeup events framework自动relax)。

注4:__pm_stay_awake和__pm_relax应成对调用。
注5:上面3个接口,均可以在中断上下文调用。

类型二(操作对象为device,为设备驱动的常用接口):

  1. 1: /* include/linux/pm_wakeup.h */
  2. 2: extern int device_wakeup_enable(struct device *dev);
  3. 3: extern int device_wakeup_disable(struct device *dev);
  4. 4: extern void device_set_wakeup_capable(struct device *dev, bool capable);
  5. 5: extern int device_init_wakeup(struct device *dev, bool val);
  6. 6: extern int device_set_wakeup_enable(struct device *dev, bool enable);
  7. 7: extern void pm_stay_awake(struct device *dev);
  8. 8: extern void pm_relax(struct device *dev);
  9. 9: extern void pm_wakeup_event(struct device *dev, unsigned int msec);

device_set_wakeup_capable,设置dev的can_wakeup标志(enable或disable,可参考5.1小节),并增加或移除该设备在sysfs相关的power文件;

device_wakeup_enable/device_wakeup_disable/device_set_wakeup_enable,对于can_wakeup的设备,使能或者禁止wakeup功能。主要是对struct wakeup_source结构的相关操作;

device_init_wakeup,设置dev的can_wakeup标志,若是enable,同时调用device_wakeup_enable使能wakeup功能;

pm_stay_awake、pm_relax、pm_wakeup_event,直接调用上面的wakeup source操作接口,操作device的struct wakeup_source变量,处理wakeup events。

5.3.1 device_set_wakeup_capable

该接口位于在drivers/base/power/wakeup.c中,代码如下:

  1. 1: void device_set_wakeup_capable(struct device *dev, bool capable)
  2. 2: {
  3. 3: if (!!dev->power.can_wakeup == !!capable)
  4. 4: return;
  5. 5:
  6. 6: if (device_is_registered(dev) && !list_empty(&dev->power.entry)) {
  7. 7: if (capable) {
  8. 8: if (wakeup_sysfs_add(dev))
  9. 9: return;
  10. 10: } else {
  11. 11: wakeup_sysfs_remove(dev);
  12. 12: }
  13. 13: }
  14. 14: dev->power.can_wakeup = capable;
  15. 15: }

该接口的实现很简单,主要包括sysfs的add/remove和can_wakeup标志的设置两部分。如果设置can_wakeup标志,则调用wakeup_sysfs_add,向该设备的sysfs目录下添加power文件夹,并注册相应的attribute文件。如果清除can_wakeup标志,执行sysfs的移除操作。

wakeup_sysfs_add/wakeup_sysfs_remove位于drivers/base/power/sysfs.c中,对wakeup events framework来说,主要包括如下的attribute文件:

  1. 1: static struct attribute *wakeup_attrs[] = {
  2. 2: #ifdef CONFIG_PM_SLEEP
  3. 3: &dev_attr_wakeup.attr,
  4. 4: &dev_attr_wakeup_count.attr,
  5. 5: &dev_attr_wakeup_active_count.attr,
  6. 6: &dev_attr_wakeup_abort_count.attr,
  7. 7: &dev_attr_wakeup_expire_count.attr,
  8. 8: &dev_attr_wakeup_active.attr,
  9. 9: &dev_attr_wakeup_total_time_ms.attr,
  10. 10: &dev_attr_wakeup_max_time_ms.attr,
  11. 11: &dev_attr_wakeup_last_time_ms.attr,
  12. 12: #ifdef CONFIG_PM_AUTOSLEEP
  13. 13: &dev_attr_wakeup_prevent_sleep_time_ms.attr,
  14. 14: #endif
  15. 15: #endif
  16. 16: NULL,
  17. 17: };
  18. 18: static struct attribute_group pm_wakeup_attr_group = {
  19. 19: .name = power_group_name,
  20. 20: .attrs = wakeup_attrs,
  21. 21: }; 1: static struct attribute *wakeup_attrs[] = {
  22. 2: #ifdef CONFIG_PM_SLEEP
  23. 3: &dev_attr_wakeup.attr,
  24. 4: &dev_attr_wakeup_count.attr,
  25. 5: &dev_attr_wakeup_active_count.attr,
  26. 6: &dev_attr_wakeup_abort_count.attr,
  27. 7: &dev_attr_wakeup_expire_count.attr,
  28. 8: &dev_attr_wakeup_active.attr,
  29. 9: &dev_attr_wakeup_total_time_ms.attr,
  30. 10: &dev_attr_wakeup_max_time_ms.attr,
  31. 11: &dev_attr_wakeup_last_time_ms.attr,
  32. 12: #ifdef CONFIG_PM_AUTOSLEEP
  33. 13: &dev_attr_wakeup_prevent_sleep_time_ms.attr,
  34. 14: #endif
  35. 15: #endif
  36. 16: NULL,
  37. 17: };
  38. 18: static struct attribute_group pm_wakeup_attr_group = {
  39. 19: .name = power_group_name,
  40. 20: .attrs = wakeup_attrs,
  41. 21: };

1)wakeup

读,获得设备wakeup功能的使能状态,返回"enabled"或"disabled"字符串。

写,更改设备wakeup功能的使能状态,根据写入的字符串("enabled"或"disabled"),调用device_set_wakeup_enable接口完成实际的状态切换。

设备wakeup功能是否使能,取决于设备的can_wakeup标志,以及设备是否注册有相应的struct wakeup_source指针。即can wakeup和may wakeup,如下:

  1. 1: /*
  2. 2: * Changes to device_may_wakeup take effect on the next pm state change.
  3. 3: */
  4. 4:
  5. 5: static inline bool device_can_wakeup(struct device *dev)
  6. 6: {
  7. 7: return dev->power.can_wakeup;
  8. 8: }
  9. 9:
  10. 10: static inline bool device_may_wakeup(struct device *dev)
  11. 11: {
  12. 12: return dev->power.can_wakeup && !!dev->power.wakeup;
  13. 13: }

2)wakeup_count

只读,获取dev->power.wakeup->event_count值。有关event_count的意义,请参考5.1小节,下同。顺便抱怨一下,这个attribute文件的命名简直糟糕透顶了!直接用event_count就是了,用什么wakeup_count,会和wakeup source中的同名字段搞混淆的!

3)wakeup_active_count,只读,获取dev->power.wakeup->active_count值。

4)wakeup_abort_count,只读,获取dev->power.wakeup->wakeup_count值。

5)wakeup_expire_count,只读,获dev->power.wakeup->expire_count取值。

6)wakeup_active,只读,获取dev->power.wakeup->active值。

7)wakeup_total_time_ms,只读,获取dev->power.wakeup->total_time值,单位为ms。

8)wakeup_max_time_ms,只读,获dev->power.wakeup->max_time取值,单位为ms。

9)wakeup_last_time_ms,只读,获dev->power.wakeup->last_time取值,单位为ms。

10)wakeup_prevent_sleep_time_ms,只读,获取dev->power.wakeup->prevent_sleep_time值,单位为ms。

注6:阅读上述代码时,我们可以看到很多类似“!!dev->power.can_wakeup == !!capable”的、带有两个“!”操作符的语句,是为了保证最后的操作对象非0即1。这从侧面反映了内核开发者的严谨程度,值得我们学习。

5.3.2 device_wakeup_enable/device_wakeup_disable/device_set_wakeup_enable

以device_wakeup_enable为例(其它类似,就不浪费屏幕了):

  1. 1: int device_wakeup_enable(struct device *dev)
  2. 2: {
  3. 3: struct wakeup_source *ws;
  4. 4: int ret;
  5. 5:
  6. 6: if (!dev || !dev->power.can_wakeup)
  7. 7: return -EINVAL;
  8. 8:
  9. 9: ws = wakeup_source_register(dev_name(dev));
  10. 10: if (!ws)
  11. 11: return -ENOMEM;
  12. 12:
  13. 13: ret = device_wakeup_attach(dev, ws);
  14. 14: if (ret)
  15. 15: wakeup_source_unregister(ws);
  16. 16:
  17. 17: return ret;
  18. 18: }

也很简单:

a)若设备指针为空,或者设备不具备wakeup能力,免谈,报错退出。

b)调用wakeup_source_register接口,以设备名为参数,创建并注册一个wakeup source。

c)调用device_wakeup_attach接口,将新建的wakeup source保存在dev->power.wakeup指针中。

wakeup_source_register接口的实现也比较简单,会先后调用wakeup_source_create、wakeup_source_prepare、wakeup_source_add等接口,所做的工作包括分配struct wakeup_source变量所需的内存空间、初始化内部变量、将新建的wakeup source添加到名称为wakeup_sources的全局链表中、等等。

device_wakeup_attach接口更为直观,不过有一点我们要关注,如果设备的dev->power.wakeup非空,也就是说之前已经有一个wakeup source了,是不允许再enable了的,会报错返回。

5.3.3 pm_stay_awake

当设备有wakeup event正在处理时,需要调用该接口通知PM core,该接口的实现如下:

  1. 1: void pm_stay_awake(struct device *dev)
  2. 2: {
  3. 3: unsigned long flags;
  4. 4:
  5. 5: if (!dev)
  6. 6: return;
  7. 7:
  8. 8: spin_lock_irqsave(&dev->power.lock, flags);
  9. 9: __pm_stay_awake(dev->power.wakeup);
  10. 10: spin_unlock_irqrestore(&dev->power.lock, flags);
  11. 11: }

呵呵,直接调用__pm_stay_awake,这也是本文的index里没有该接口的原因。接着看代码。

  1. 1: void __pm_stay_awake(struct wakeup_source *ws)
  2. 2: {
  3. 3: unsigned long flags;
  4. 4:
  5. 5: if (!ws)
  6. 6: return;
  7. 7:
  8. 8: spin_lock_irqsave(&ws->lock, flags);
  9. 9:
  10. 10: wakeup_source_report_event(ws);
  11. 11: del_timer(&ws->timer);
  12. 12: ws->timer_expires = 0;
  13. 13:
  14. 14: spin_unlock_irqrestore(&ws->lock, flags);
  15. 15: }

由于pm_stay_awake报告的event需要经过pm_relax主动停止,因此就不再需要timer,所以__pm_stay_awake实现是直接调用wakeup_source_report_event,然后停止timer。接着看代码:

  1. 1: static void wakeup_source_report_event(struct wakeup_source *ws)
  2. 2: {
  3. 3: ws->event_count++;
  4. 4: /* This is racy, but the counter is approximate anyway. */
  5. 5: if (events_check_enabled)
  6. 6: ws->wakeup_count++;
  7. 7:
  8. 8: if (!ws->active)
  9. 9: wakeup_source_activate(ws);
  10. 10: }

a)增加wakeup source的event_count,表示该source又产生了一个event。

b)根据events_check_enabled变量的状态,决定是否增加wakeup_count。这和wakeup count的功能有关,到时再详细描述。

c)如果wakeup source没有active,则调用wakeup_source_activate,activate之。这也是5.1小节所描述的,event_count和active_count的区别所在。wakeup_source_activate的代码如下。

  1. 1: static void wakeup_source_activate(struct wakeup_source *ws)
  2. 2: {
  3. 3: unsigned int cec;
  4. 4:
  5. 5: /*
  6. 6: * active wakeup source should bring the system
  7. 7: * out of PM_SUSPEND_FREEZE state
  8. 8: */
  9. 9: freeze_wake();
  10. 10:
  11. 11: ws->active = true;
  12. 12: ws->active_count++;
  13. 13: ws->last_time = ktime_get();
  14. 14: if (ws->autosleep_enabled)
  15. 15: ws->start_prevent_time = ws->last_time;
  16. 16:
  17. 17: /* Increment the counter of events in progress. */
  18. 18: cec = atomic_inc_return(&combined_event_count);
  19. 19:
  20. 20: trace_wakeup_source_activate(ws->name, cec);
  21. 21: }

a)调用freeze_wake,将系统从suspend to freeze状态下唤醒。有关freeze功能,请参考相关的文章。

b)设置active标志,增加active_count,更新last_time。

c)如果使能了autosleep,更新start_prevent_time,因为此刻该wakeup source会开始阻止系统auto sleep。具体可参考auto sleep的功能描述。

d)增加“wakeup events in progress”计数(5.2小节有描述)。该操作是wakeup events framework的灵魂,增加该计数,意味着系统正在处理的wakeup event数目不为零,则系统不能suspend。

到此,pm_stay_awake执行结束,意味着系统至少正在处理一个wakeup event,因此不能suspend。那处理完成后呢?driver要调用pm_relax通知PM core。

5.3.4 pm_relax

pm_relax和pm_stay_awake成对出现,用于在event处理结束后通知PM core,其实现如下:

  1. 1: /**
  2. 2: * pm_relax - Notify the PM core that processing of a wakeup event has ended.
  3. 3: * @dev: Device that signaled the event.
  4. 4: *
  5. 5: * Execute __pm_relax() for the @dev's wakeup source object.
  6. 6: */
  7. 7: void pm_relax(struct device *dev)
  8. 8: {
  9. 9: unsigned long flags;
  10. 10:
  11. 11: if (!dev)
  12. 12: return;
  13. 13:
  14. 14: spin_lock_irqsave(&dev->power.lock, flags);
  15. 15: __pm_relax(dev->power.wakeup);
  16. 16: spin_unlock_irqrestore(&dev->power.lock, flags);
  17. 17: }

直接调用__pm_relax,如下:

  1. 1: void __pm_relax(struct wakeup_source *ws)
  2. 2: {
  3. 3: unsigned long flags;
  4. 4:
  5. 5: if (!ws)
  6. 6: return;
  7. 7:
  8. 8: spin_lock_irqsave(&ws->lock, flags);
  9. 9: if (ws->active)
  10. 10: wakeup_source_deactivate(ws);
  11. 11: spin_unlock_irqrestore(&ws->lock, flags);
  12. 12: }

如果该wakeup source处于active状态,调用wakeup_source_deactivate接口,deactivate之。deactivate接口和activate接口一样,是wakeup events framework的核心逻辑,如下:

  1. 1: static void wakeup_source_deactivate(struct wakeup_source *ws)
  2. 2: {
  3. 3: unsigned int cnt, inpr, cec;
  4. 4: ktime_t duration;
  5. 5: ktime_t now;
  6. 6:
  7. 7: ws->relax_count++;
  8. 8: /*
  9. 9: * __pm_relax() may be called directly or from a timer function.
  10. 10: * If it is called directly right after the timer function has been
  11. 11: * started, but before the timer function calls __pm_relax(), it is
  12. 12: * possible that __pm_stay_awake() will be called in the meantime and
  13. 13: * will set ws->active. Then, ws->active may be cleared immediately
  14. 14: * by the __pm_relax() called from the timer function, but in such a
  15. 15: * case ws->relax_count will be different from ws->active_count.
  16. 16: */
  17. 17: if (ws->relax_count != ws->active_count) {
  18. 18: ws->relax_count--;
  19. 19: return;
  20. 20: }
  21. 21:
  22. 22: ws->active = false;
  23. 23:
  24. 24: now = ktime_get();
  25. 25: duration = ktime_sub(now, ws->last_time);
  26. 26: ws->total_time = ktime_add(ws->total_time, duration);
  27. 27: if (ktime_to_ns(duration) > ktime_to_ns(ws->max_time))
  28. 28: ws->max_time = duration;
  29. 29:
  30. 30: ws->last_time = now;
  31. 31: del_timer(&ws->timer);
  32. 32: ws->timer_expires = 0;
  33. 33:
  34. 34: if (ws->autosleep_enabled)
  35. 35: update_prevent_sleep_time(ws, now);
  36. 36:
  37. 37: /*
  38. 38: * Increment the counter of registered wakeup events and decrement the
  39. 39: * couter of wakeup events in progress simultaneously.
  40. 40: */
  41. 41: cec = atomic_add_return(MAX_IN_PROGRESS, &combined_event_count);
  42. 42: trace_wakeup_source_deactivate(ws->name, cec);
  43. 43:
  44. 44:
  45. 45: split_counters(&cnt, &inpr);
  46. 46: if (!inpr && waitqueue_active(&wakeup_count_wait_queue))
  47. 47: wake_up(&wakeup_count_wait_queue);
  48. 48: }

a)relax_count加1(如果relax_count和active_count不等,则说明有重复调用,要退出)。

b)清除active标记。

c)更新total_time、max_time、last_time等变量。

d)如果使能auto sleep,更新相关的变量(后面再详细描述)。

e)再欣赏一下艺术,wakeup events in progress减1,registered wakeup events加1。

f)wakeup count相关的处理,后面再详细说明。

5.3.5 pm_wakeup_event

pm_wakeup_event是pm_stay_awake和pm_relax的组合版,在上报event时,指定一个timeout时间,timeout后,自动relax,一般用于不知道何时能处理完成的场景。该接口比较简单,就不一一描述了。

5.3.6 pm_wakeup_pending

drivers产生的wakeup events,最终要上报到PM core,PM core会根据这些events,决定是否要终止suspend过程。这表现在suspend过程中频繁调用pm_wakeup_pending接口上(可参考“Linux电源管理(6)_Generic PM之Suspend功能”)。该接口的实现如下:

  1. 1: /**
  2. 2: * pm_wakeup_pending - Check if power transition in progress should be aborted.
  3. 3: *
  4. 4: * Compare the current number of registered wakeup events with its preserved
  5. 5: * value from the past and return true if new wakeup events have been registered
  6. 6: * since the old value was stored. Also return true if the current number of
  7. 7: * wakeup events being processed is different from zero.
  8. 8: */
  9. 9: bool pm_wakeup_pending(void)
  10. 10: {
  11. 11: unsigned long flags;
  12. 12: bool ret = false;
  13. 13:
  14. 14: spin_lock_irqsave(&events_lock, flags);
  15. 15: if (events_check_enabled) {
  16. 16: unsigned int cnt, inpr;
  17. 17:
  18. 18: split_counters(&cnt, &inpr);
  19. 19: ret = (cnt != saved_count || inpr > 0);
  20. 20: events_check_enabled = !ret;
  21. 21: }
  22. 22: spin_unlock_irqrestore(&events_lock, flags);
  23. 23:
  24. 24: if (ret)
  25. 25: print_active_wakeup_sources();
  26. 26:
  27. 27: return ret;
  28. 28: }

该接口的逻辑比较直观,先抛开wakeup count的逻辑不谈(后面会重点说明),只要正在处理的events不为0,就返回true,调用者就会终止suspend。

5.4 wakeup count、wake lock和auto sleep

这篇文章写的有点长了,不能继续了,这几个功能,会接下来的文章中继续分析。

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