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_t state_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)
#ifdef CONFIG_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);
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; // 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 void early_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 void early_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 void late_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);
}