Linux Power（一）： kernel/power/earlysuspend.c

 /* kernel/power/earlysuspend.c
  *
  * Copyright (C) 2005-2008 Google, Inc.
  *
  * This software is licensed under the terms of the GNU General Public
  * License version 2, as published by the Free Software Foundation, and
  * may be copied, distributed, and modified under those terms.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  */

 #include <linux/earlysuspend.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
 #include <linux/rtc.h>
 #include <linux/wakelock.h>
 #include <linux/workqueue.h>

 #include "power.h"

 enum {
     DEBUG_USER_STATE = 1U << ,
     DEBUG_SUSPEND = 1U << ,
     DEBUG_VERBOSE = 1U << ,
 };
 static int debug_mask = DEBUG_USER_STATE;
 module_param_named(debug_mask, debug_mask, int, S_IRUGO | S_IWUSR | S_IWGRP);

 static DEFINE_MUTEX(early_suspend_lock);
 static LIST_HEAD(early_suspend_handlers);
 static void early_suspend(struct work_struct *work);
 static void late_resume(struct work_struct *work);
 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;

 void register_early_suspend(struct early_suspend *handler)
 {
     struct list_head *pos;

     mutex_lock(&early_suspend_lock);
     list_for_each(pos, &early_suspend_handlers) {
         struct early_suspend *e;
         e = list_entry(pos, struct early_suspend, link);
         if (e->level > handler->level)
             break;
     }
     list_add_tail(&handler->link, pos);
     if ((state & SUSPENDED) && handler->suspend)
         handler->suspend(handler);
     mutex_unlock(&early_suspend_lock);
 }
 EXPORT_SYMBOL(register_early_suspend);

 void unregister_early_suspend(struct early_suspend *handler)
 {
     mutex_lock(&early_suspend_lock);
     list_del(&handler->link);
     mutex_unlock(&early_suspend_lock);
 }
 EXPORT_SYMBOL(unregister_early_suspend);
 

register_early_suspend(struct early_suspend *handler)会按照level从小到大的方式，将handler依次挂在early_suspend_handlers链表头上。

if (e->level > handler->level)判断链表节点e的level大于要插入的handler的level时就break当前遍历，用list_add_tail(&handler->link, pos);将handler->link插到pos节点的前面。

  static void early_suspend(struct work_struct *work)
  {
      struct early_suspend *pos;
      unsigned long irqflags;
      int abort = ;

      mutex_lock(&early_suspend_lock);
      spin_lock_irqsave(&state_lock, irqflags);
      if (state == SUSPEND_REQUESTED)
          state |= SUSPENDED;
      else
          abort = ;
      spin_unlock_irqrestore(&state_lock, irqflags);

      if (abort) {
          if (debug_mask & DEBUG_SUSPEND)
              pr_info("early_suspend: abort, state %d\n", state);
          mutex_unlock(&early_suspend_lock);
          goto abort;
      }

      if (debug_mask & DEBUG_SUSPEND)
          pr_info("early_suspend: call handlers\n");
      list_for_each_entry(pos, &early_suspend_handlers, link) {
          if (pos->suspend != NULL) {
              if (debug_mask & DEBUG_VERBOSE)
                  pr_info("early_suspend: calling %pf\n", pos->suspend);
             pos->suspend(pos);
         }
     }
     mutex_unlock(&early_suspend_lock);

     suspend_sys_sync_queue();
 abort:
     spin_lock_irqsave(&state_lock, irqflags);
     if (state == SUSPEND_REQUESTED_AND_SUSPENDED)
         wake_unlock(&main_wake_lock);
     spin_unlock_irqrestore(&state_lock, irqflags);
 }

 static void late_resume(struct work_struct *work)
 {
     struct early_suspend *pos;
     unsigned long irqflags;
     int abort = ;

     mutex_lock(&early_suspend_lock);
     spin_lock_irqsave(&state_lock, irqflags);
     if (state == SUSPENDED)
         state &= ~SUSPENDED;
     else
         abort = ;
     spin_unlock_irqrestore(&state_lock, irqflags);

     if (abort) {
         if (debug_mask & DEBUG_SUSPEND)
             pr_info("late_resume: abort, state %d\n", state);
         goto abort;
     }
     if (debug_mask & DEBUG_SUSPEND)
         pr_info("late_resume: call handlers\n");
     list_for_each_entry_reverse(pos, &early_suspend_handlers, link) {
         if (pos->resume != NULL) {
             if (debug_mask & DEBUG_VERBOSE)
                 pr_info("late_resume: calling %pf\n", pos->resume);

             pos->resume(pos);
         }
     }
     if (debug_mask & DEBUG_SUSPEND)
         pr_info("late_resume: done\n");
 abort:
     mutex_unlock(&early_suspend_lock);
 }

early_suspend(struct work_struct *work)和late_resume(struct work_struct *work)分别在第37、38行被声明为了early_suspend_work和late_resume_work，以便在

request_suspend_state(suspend_state_t new_state)中的suspend_work_queue工作队列中使用。

ealry_suspend(struct work_struct *work)中最关键的一句list_for_each_entry(pos, &early_suspend_handlers, link)，表示按照level等级排列的顺序，依次调用pos所指向的各个
驱动中注册的ealrysuspend 指向的suspend handler。

late_resume(struct work_struct *work)中list_for_each_entry_reverse(pos, &early_suspend_handlers, link)，表示按照level等级的逆序，依次调用pos所指向的各个
驱动中注册的earlysuspend 指向的resume handler。
 
这里有一个很有用的调试信息：pr_info("late_resume: calling %pf\n", pos->resume); %pf可以打印被调函数的函数名。

 void request_suspend_state(suspend_state_t new_state)
 {
     unsigned long irqflags;
     int old_sleep;

     spin_lock_irqsave(&state_lock, irqflags);
     old_sleep = state & SUSPEND_REQUESTED;
     if (debug_mask & DEBUG_USER_STATE) {
         struct timespec ts;
         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 + , tm.tm_mon + , tm.tm_mday,
             tm.tm_hour, tm.tm_min, tm.tm_sec, ts.tv_nsec);
     }
     if (!old_sleep && new_state != PM_SUSPEND_ON) {
         state |= SUSPEND_REQUESTED;
         queue_work(suspend_work_queue, &early_suspend_work);
     } else if (old_sleep && new_state == PM_SUSPEND_ON) {
         state &= ~SUSPEND_REQUESTED;
         wake_lock(&main_wake_lock);
         queue_work(suspend_work_queue, &late_resume_work);
     }
     requested_suspend_state = new_state;
     spin_unlock_irqrestore(&state_lock, irqflags);
 }

 suspend_state_t get_suspend_state(void)
 {
     return requested_suspend_state;
 }

request_suspend_state(suspend_state_t new_state)会被kernel/power/main.c中的state show调用，main.c将会在下一章详细说明。

request_suspend_state(suspend_state_t new_state)传入的参数new_state的类型suspend_state_t为一个typedef类型的变量：typedef int __bitwise suspend_state_t;

当new_state为0时，request_suspend_state调用queue_work(suspend_work_queue, &late_resume_work);分支进行late唤醒。
当new_state为3时，request_suspend_state调用queue_work(suspend_work_queue, &early_suspend_work);分支进行浅度休眠。

当系统休眠/唤醒时，串口上会出现如下打印：
request_suspend_state: sleep (0->3) at 6442598858519 (2012-02-05 01:31:08.172285684 UTC)
request_suspend_state: wakeup (3->0) at 6464854624023 (2012-02-05 01:31:30.428053438 UTC)
0代表唤醒，3代表休眠。
0->3 从唤醒到休眠(sleep);
3->0 从休眠到唤醒(wakeup);