Android在标准linux基础上对休眠唤醒的实现(一)

说明：

1.Based on linux 2.6.32 and android 2.2，only support SDR(mem).

2.参考文章：

http://2695477.blog.51cto.com/blog/2685477/484751

http://www.docin.com/p-115475680.html

http://blogold.chinaunix.net/u3/113927/showart_2447111.html

http://www.cnmsdn.com/html/201003/1269407632ID2530.html

 

 

一、新增特性介绍

 

实际上，android仍然是利用了标准linux的休眠唤醒系统，只不过添加了一些使用上的新特性，early suspend、late resume、wake lock。

 

Early suspend- 这个机制定义了在suspend的早期，关闭显示屏的时候，一些和显示屏相关的设备，比如背光、重力感应器和触摸屏等设备都应该被关掉，但是此时系统可能还有持有wake lock的任务在运行，如音乐播放，电话，或者扫描sd卡上的文件等，这个时候整个系统还不能进入真正睡眠，直到所有的wake lock都没释放。在嵌入式设备中，悲观是一个很大的电源消耗，所有android加入了这种机制。

 

Late resume -这个机制定义了在resume的后期，也就是唤醒源已经将处理器唤醒，标准linux的唤醒流程已经走完了，在android上层系统识别出这个物理上的唤醒源是上层定义的，那么上层将会发出late resume的命令给下层，这个时候将会调用相关设备注册的late resume回调函数。

 

Wake lock - wakelock在android的电源管理系统中扮演一个核心的角色，wakelock是一种锁的机制,只要有task拿着这个锁,系统就无法进入休眠,可以被用户态进程和内核线程获得。这个锁可以是有超时的或者是没有超时的,超时的锁会在时间过去以后自动解锁。如果没有锁了或者超时了,内核就会启动标准linux的那套休眠机制机制来进入休眠。

 

二、kernel层源码解析 - early suspend 和 late resume实现

相关源码：

kernel/kernel/power/main.c

kernel/kernel/power/earlysuspend.c

kernel/kernel/power/wakelock.c

kernel/kernel/power/userwakelock.c

kernel/kernel/power/suspend.c

 

之前标准的linux的sysfs的接口只需要一个state就够了，现在至少需要3个接口文件：state、wake_lock、wake_unlock。现在为了配合android为休眠唤醒添加的几种新特性，可以填入文件state的模式又多了一种：on,标准android系统中只支持state的on和mem模式，其余的暂不支持。wake_lock和wake_unlock接口对应的读写函数在文件userwakelock.c中，对wakelock.c中的create wakelock或者release wakelock进行了封装，供用户空间来使用。

 

如果上层用户执行:echo xxx(on or mem) > sys/power/state的话，将会调用到如下函数：

static ssize_tstate_store(struct kobject *kobj, struct kobj_attribute *attr,

const char *buf, size_t n)

{

#ifdef CONFIG_SUSPEND// set

#ifdef CONFIG_EARLYSUSPEND   //set

      suspend_state_t state = PM_SUSPEND_ON;  // for early suspend and late resume

#else

      suspend_state_t state = PM_SUSPEND_STANDBY;

#endif

      const char * const *s;

#endif

      char *p;

      int len;

      int error = -EINVAL;

 

      p = memchr(buf, '/n', n);

      len = p ? p - buf : n;

 

      /* First, check if we are requested to hibernate */

      if (len == 4 && !strncmp(buf, "disk", len)) {

             error = hibernate();  //检查是否要求进入disk省电模式，暂时不支持

 goto Exit;

      }

 

#ifdef CONFIG_SUSPEND       // def

      for (s = &pm_states[state]; state < PM_SUSPEND_MAX; s++, state++) {

             if (*s && len == strlen(*s) && !strncmp(buf, *s, len))

                    break;

      }

      if (state < PM_SUSPEND_MAX && *s)

#ifdefCONFIG_EARLYSUSPEND

             if (state == PM_SUSPEND_ON || valid_state(state)) {

//需要经过平台pm.c文件定义的模式支持检查函数，mtk只支持mem，同时如果是android发送出来的late resume命令(on)，这里也会放行，往下执行

                    error = 0;

                    request_suspend_state(state);    // android休眠唤醒的路线

             }

#else

             error = enter_state(state);//标准linux休眠唤醒的路线

#endif

#endif

 

 Exit:

      return error ? error : n;

}

 

@ kernel/kernel/power/earlysuspend.c

enum {

      DEBUG_USER_STATE = 1U << 0,

      DEBUG_SUSPEND = 1U << 2,

};

int Earlysuspend_debug_mask = DEBUG_USER_STATE;

module_param_named(Earlysuspend_debug_mask, Earlysuspend_debug_mask, int, S_IRUGO | S_IWUSR | S_IWGRP);

 

static DEFINE_MUTEX(early_suspend_lock);

static LIST_HEAD(early_suspend_handlers);

static void early_sys_sync(struct work_struct *work);

static void early_suspend(struct work_struct *work);

static void late_resume(struct work_struct *work);

static DECLARE_WORK(early_sys_sync_work, early_sys_sync);

static DECLARE_WORK(early_suspend_work, early_suspend);

static DECLARE_WORK(late_resume_work, late_resume);

static DEFINE_SPINLOCK(state_lock);

enum {

      SUSPEND_REQUESTED = 0x1,

      SUSPENDED = 0x2,

      SUSPEND_REQUESTED_AND_SUSPENDED = SUSPEND_REQUESTED | SUSPENDED,

};

static int state;            // 初始化为0

 

static DECLARE_COMPLETION(fb_drv_ready);

 

voidrequest_suspend_state(suspend_state_t new_state)

{

      unsigned long irqflags;

      int old_sleep;

 

      spin_lock_irqsave(&state_lock, irqflags);

      old_sleep = state & SUSPEND_REQUESTED;// state = 1 or 3

// state的值会在0->1->3->2->0循环变化，后面分析代码都可以看出这些值代表系统目前处于什么阶段，简单得说就是：正常->准备进early suspend->开始early suspend并且对名为mian的wakelock解锁，如果此时没有其余wakelock处于lock状态，那么系统就走linux的休眠唤醒路线让整个系统真正休眠，直到唤醒源发生，然后将处理器和linux层唤醒。之后android层判断本次底层醒来是由于我所定义的唤醒源引起的吗？如果不是，android将不予理会，过段时间没有wakelock锁，系统会再次走linux的休眠路线进入休眠。如果是，那么android上层就会写一个on的指令到state接口中，同样是会调用到函数request_suspend_state()->准备执行late resume-> 开始执行late resume，之后整个系统就这样被唤醒了。

      if (Earlysuspend_debug_mask & DEBUG_USER_STATE) {

             struct timespec ts;        //打印出debug信息

             struct rtc_time tm;

             getnstimeofday(&ts);

             rtc_time_to_tm(ts.tv_sec, &tm);

             pr_info("[request_suspend_state]: %s (%d->%d) at %lld "

                    "(%d-%02d-%02d %02d:%02d:%02d.%09lu UTC)/n",

                    new_state != PM_SUSPEND_ON ? "sleep" : "wakeup",

                    requested_suspend_state, new_state,

                    ktime_to_ns(ktime_get()),

                    tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,

                    tm.tm_hour, tm.tm_min, tm.tm_sec, ts.tv_nsec);

      }

// eg: [request_suspend_state]: sleep (0->3) at 97985478409 (2010-01-03 09:52:59.637902305 UTC)，这里对时间的获取和处理，在其他地方可以参考

      // ready to enter earlysuspend

      if (!old_sleep && new_state != PM_SUSPEND_ON) {// susepnd会进入这里

             state |= SUSPEND_REQUESTED;    // state = 1

             pr_info("[request_suspend_state]:

sys_sync_work_queue early_sys_sync_work/n");

             queue_work(sys_sync_work_queue, &early_sys_sync_work);

             pr_info("[request_suspend_state]: suspend_work_queue early_suspend_work/n");

             queue_work(suspend_work_queue, &early_suspend_work);

//在wakelocks_init()函数(wakelock.c)中会创建这两个工作队列和工作者线程来专门负责处理sys_sync和early suspend的工作。关于工作队列的详情参考我工作队列的文章

      }

      // ready to enter lateresume

      else if (old_sleep && new_state == PM_SUSPEND_ON) {

             state &= ~SUSPEND_REQUESTED; // state = 2

             wake_lock(&main_wake_lock);         // 对main wakelock上锁

             pr_info("[request_suspend_state]: suspend_work_queue late_resume_work/n" );

             if (queue_work(suspend_work_queue, &late_resume_work)) {

//提交late resume的工作项

           //

           //  In order to synchronize the backlight turn on timing,

           //  block the thread and wait for fb driver late_resume()

                 //  callback function is completed

                 //

           wait_for_completion(&fb_drv_ready);     

//等待完成量fb_drv_ready，他会在late resume结束之后完成

       }

      }

      requested_suspend_state = new_state;     

//存储本次休眠或者是唤醒的状态，供下次休眠或者唤醒使用

      spin_unlock_irqrestore(&state_lock, irqflags);

}

 

在系统suspend的时候提交的两个工作项会陆续被执行到，那么下面就来看一下执行early suspend的关键函数。

static voidearly_sys_sync(struct work_struct *work)

{

      wake_lock(&sys_sync_wake_lock);

      printk("[sys_sync work] start/n");

      sys_sync();    //同步文件系统

      printk("[sys_sync wrok] done/n");

      wake_unlock(&sys_sync_wake_lock);

}

 

static voidearly_suspend(struct work_struct *work)

{

      struct early_suspend *pos;

      unsigned long irqflags;

      int abort = 0;

 

      mutex_lock(&early_suspend_lock);

      spin_lock_irqsave(&state_lock, irqflags);

      if (state == SUSPEND_REQUESTED)

             state |= SUSPENDED; // state = 3

      else

             abort = 1;

      spin_unlock_irqrestore(&state_lock, irqflags);

 

      if (abort) {     // suspend中止退出

             if (Earlysuspend_debug_mask & DEBUG_SUSPEND)

                    pr_info("[early_suspend]: abort, state %d/n", state);

             mutex_unlock(&early_suspend_lock);

             goto abort;

      }

 

      if (Earlysuspend_debug_mask & DEBUG_SUSPEND)

             pr_info("[early_suspend]: call handlers/n");

      list_for_each_entry(pos, &early_suspend_handlers, link) {

             if (pos->suspend != NULL)

                    pos->suspend(pos);

      }

//函数register_early_suspend()会将每一个early suspend项以优先级大小注册到链表early_suspend_handlers中，这里就是一次取出，然后执行对应的early suspend回调函数

      mutex_unlock(&early_suspend_lock);

 

      // Remove sys_sync from early_suspend,

      // and use work queue to complete sys_sync

 

abort:

      spin_lock_irqsave(&state_lock, irqflags);

      if (state == SUSPEND_REQUESTED_AND_SUSPENDED)

      {

             pr_info("[early_suspend]: wake_unlock(main)/n");

             wake_unlock(&main_wake_lock);

// main wakelock解锁。看到这里，好像系统执行了early suspend之后就没有往下执行标准linux的suspend流程了，其实不是，android的做法是，不是你执行完了early suspend  的回调就可以马上走标准linux的suspend流程，而是会检查还有没有wakelock被持有，如果所有wakelock全是解锁状态，那么就会执行标准linux的suspend步骤。

}

      spin_unlock_irqrestore(&state_lock, irqflags);

}

 

static voidlate_resume(struct work_struct *work)

{

      struct early_suspend *pos;

      unsigned long irqflags;

      int abort = 0;

   int completed = 0;

 

      mutex_lock(&early_suspend_lock);

      spin_lock_irqsave(&state_lock, irqflags);

 

   // return back from suspend

      if (state == SUSPENDED)

             state &= ~SUSPENDED;    // state = 0

      else

             abort = 1;

      spin_unlock_irqrestore(&state_lock, irqflags);

 

      if (abort) {

             if (Earlysuspend_debug_mask & DEBUG_SUSPEND)

                    pr_info("[late_resume]: abort, state %d/n", state);

             goto abort;

      }

      if (Earlysuspend_debug_mask & DEBUG_SUSPEND)

             pr_info("[late_resume]: call handlers/n");

      list_for_each_entry_reverse(pos, &early_suspend_handlers, link)

   {

       if (!completed && pos->level < EARLY_SUSPEND_LEVEL_DISABLE_FB) {

           complete(&fb_drv_ready);

           completed = 1;

       }

             if (pos->resume != NULL)

                    pos->resume(pos);

   }

//以和early suspend的逆序执行链表early_suspend_handlers上的late resume回调函数

if (Earlysuspend_debug_mask & DEBUG_SUSPEND)

             pr_info("[late_resume]: done/n");

abort:

   if (!completed)

       complete(&fb_drv_ready);   //设置完成量ok

    mutex_unlock(&early_suspend_lock);

}