Android中休眠与唤醒之wake_lock, early_suspend, late_resume

最近研究如何让Android不休眠。听组里人说，机器在充电的时候不休眠。我试了一下，确实是，串口可以使用（CONFIG_PM_DEBUG并没有打开）。
这个时候，LCD显示屏是休眠了，触摸屏也休眠了，其他的比如重力传感器等就没有看了，但是标准的Linux系统并没有进入休眠。看了网上好多关于Android系统的休眠与唤醒

例子，感觉有些懵懵懂懂的。于是，还是看内核代码吧。

Android在标准的Linux休眠与唤醒机制上又加了一层，就是early_suspend / late_resume。顾名思意，使用early_suspend（）进行休眠的设备，它休眠的时刻早于其他设备，使用late_resume（）唤醒的设备，它被唤醒的时刻要晚于其他设备。这对函数通常成对出现，当内核打开了CONFIG_EARLY_SUSPEND(Android默认打开)后，就可以使

用这组函数来代替驱动中标准的 suspend / resume接口。

好了，讲到early_suspend和late_resume，似乎必须要扯到一种叫做wake_lock的锁定机制了。其实，单纯从某个设备的驱动程序上来讲，未必需要用到wake_lock机制，

比如我们的触摸屏驱动中使用了early_suspend，就没有使用wake_lock.

目前，我了解到的，wake_lock的用途只有一个，那就是防止系统进入休眠（这里的休眠，指的是标准的Linux的休眠，不包含使用early_suspend（）进行休眠的设备，

使用early_suspend()的设备，在系统还有wake_lock锁的时候，也是要休眠的）。

好吧，现在是时候分析下Android/Linux的休眠与唤醒了，虽然好多先人 都已经讲了这些，而且讲的还不错，这里我还是要提一下。

root@android:/ # ls /sys/power/

pm_async

state

wait_for_fb_sleep

wait_for_fb_wake

wake_lock

wake_unlock

wakeup_count

这里，我只关注state，当state 的值变化时，内核会调用

[cpp]
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static ssize_t state_store(struct kobject *kobj, struct kobj_attribute *attr,
const char *buf, size_t n)
{
#ifdef CONFIG_SUSPEND
#ifdef CONFIG_EARLYSUSPEND
suspend_state_t state = PM_SUSPEND_ON;
#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();
goto Exit;
}

#ifdef CONFIG_SUSPEND
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)) {
error = 0;
request_suspend_state(state);//这里，进入了Android的休眠与唤醒的处理函数
}
#else

error = enter_state(state);
#endif

#endif

Exit:
return error ? error : n;
}

power_attr(state);

static ssize_t state_store(struct kobject *kobj, struct kobj_attribute *attr,
const char *buf, size_t n)
{
#ifdef CONFIG_SUSPEND
#ifdef CONFIG_EARLYSUSPEND
suspend_state_t state = PM_SUSPEND_ON;
#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();
goto Exit;
}

#ifdef CONFIG_SUSPEND
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)) {
error = 0;
request_suspend_state(state);//这里，进入了Android的休眠与唤醒的处理函数
}
#else
error = enter_state(state);
#endif
#endif

Exit:
return error ? error : n;
}

power_attr(state);

看看

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request_suspend_state()都干了些什么事情

request_suspend_state()都干了些什么事情

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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 + 1900, tm.tm_mon + 1, 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);//在休眠的时候，去遍历执行early_suspend_work这个队列
} 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);//在唤醒的时候，去遍历执行late_resume_work这个队列
}
requested_suspend_state = new_state;
spin_unlock_irqrestore(&state_lock, irqflags);
}

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 + 1900, tm.tm_mon + 1, 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);//在休眠的时候，去遍历执行early_suspend_work这个队列
} 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);//在唤醒的时候，去遍历执行late_resume_work这个队列
}
requested_suspend_state = new_state;
spin_unlock_irqrestore(&state_lock, irqflags);
}

怎么样，是不是很简单，根据用户/系统所请求的状态，去做相应的动作（休眠/唤醒）
能用到的一些变量的声明在这里

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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 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);

看名字也知道了，early_suspend这个函数指针来处理early_suspend_work这条队列，late_resume 这个函数指针来处理late_resume_work这条队列。

虽然函数early_suspend()和late_resume()的实现都非常易懂，这里还是要贴出来，因为还有些东西要分析一下。

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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;
else
abort = 1;
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) {//这里就是关键了，遍历early_suspend_handler这条链表（在驱动中注册early_suspend的时候，都注册到这条链表上了）
if (pos->suspend != NULL) {
if (debug_mask & DEBUG_VERBOSE)
pr_info("early_suspend: calling %pf\n", pos->suspend);
pos->suspend(pos);//调用各个实现进行各设备的休眠
}
}
mutex_unlock(&early_suspend_lock);

if (debug_mask & DEBUG_SUSPEND)
pr_info("early_suspend: sync\n");

sys_sync();
abort:
spin_lock_irqsave(&state_lock, irqflags);
if (state == SUSPEND_REQUESTED_AND_SUSPENDED)
wake_unlock(&main_wake_lock);//这里很重要，别小看这个一个wake_unlock,起初我也以为这仅仅是一个释放main锁，其实里面有玄机呢。还记得wake_lock主要用来干嘛么，用来防止系统休眠，也就是说，只要系统中其他地方还拥有wake_lock锁（类型WAKE_LOCK_SUSPEND），系统就没法进入休眠，如果没有锁了，那就要接着走标准Linux的那一套休眠机制了
spin_unlock_irqrestore(&state_lock, irqflags);
}

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;
else
abort = 1;
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) {//这里就是关键了，遍历early_suspend_handler这条链表（在驱动中注册early_suspend的时候，都注册到这条链表上了）
if (pos->suspend != NULL) {
if (debug_mask & DEBUG_VERBOSE)
pr_info("early_suspend: calling %pf\n", pos->suspend);
pos->suspend(pos);//调用各个实现进行各设备的休眠
}
}
mutex_unlock(&early_suspend_lock);

if (debug_mask & DEBUG_SUSPEND)
pr_info("early_suspend: sync\n");

sys_sync();
abort:
spin_lock_irqsave(&state_lock, irqflags);
if (state == SUSPEND_REQUESTED_AND_SUSPENDED)
wake_unlock(&main_wake_lock);//这里很重要，别小看这个一个wake_unlock,起初我也以为这仅仅是一个释放main锁，其实里面有玄机呢。还记得wake_lock主要用来干嘛么，用来防止系统休眠，也就是说，只要系统中其他地方还拥有wake_lock锁（类型WAKE_LOCK_SUSPEND），系统就没法进入休眠，如果没有锁了，那就要接着走标准Linux的那一套休眠机制了
spin_unlock_irqrestore(&state_lock, irqflags);
}

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先跳过late_resume()。来看下wake_unlock()的实现吧

[cpp] view plaincopyprint?void wake_unlock(struct wake_lock *lock)
{
int type;
unsigned long irqflags;
spin_lock_irqsave(&list_lock, irqflags);
type = lock->flags & WAKE_LOCK_TYPE_MASK;
#ifdef CONFIG_WAKELOCK_STAT
wake_unlock_stat_locked(lock, 0);
#endif
if (debug_mask & DEBUG_WAKE_LOCK)
pr_info("wake_unlock: %s\n", lock->name);
lock->flags &= ~(WAKE_LOCK_ACTIVE | WAKE_LOCK_AUTO_EXPIRE);
list_del(&lock->link);
list_add(&lock->link, &inactive_locks);
if (type == WAKE_LOCK_SUSPEND) {//类型，驱动中一般只有这一种类型
long has_lock = has_wake_lock_locked(type);
if (has_lock > 0) {
if (debug_mask & DEBUG_EXPIRE)
pr_info("wake_unlock: %s, start expire timer, "
"%ld\n", lock->name, has_lock);
mod_timer(&expire_timer, jiffies + has_lock);
} else {
if (del_timer(&expire_timer))
if (debug_mask & DEBUG_EXPIRE)
pr_info("wake_unlock: %s, stop expire "
"timer\n", lock->name);
if (has_lock == 0)//如果没有锁了，要进入标准Linux的休眠机制了，咱们接着往下跟
queue_work(suspend_work_queue, &suspend_work);
}
if (lock == &main_wake_lock) {
if (debug_mask & DEBUG_SUSPEND)
print_active_locks(WAKE_LOCK_SUSPEND);
#ifdef CONFIG_WAKELOCK_STAT
update_sleep_wait_stats_locked(0);
#endif
}
}
spin_unlock_irqrestore(&list_lock, irqflags);
}
EXPORT_SYMBOL(wake_unlock);

void wake_unlock(struct wake_lock *lock)
{
int type;
unsigned long irqflags;
spin_lock_irqsave(&list_lock, irqflags);
type = lock->flags & WAKE_LOCK_TYPE_MASK;
#ifdef CONFIG_WAKELOCK_STAT
wake_unlock_stat_locked(lock, 0);
#endif
if (debug_mask & DEBUG_WAKE_LOCK)
pr_info("wake_unlock: %s\n", lock->name);
lock->flags &= ~(WAKE_LOCK_ACTIVE | WAKE_LOCK_AUTO_EXPIRE);
list_del(&lock->link);
list_add(&lock->link, &inactive_locks);
if (type == WAKE_LOCK_SUSPEND) {//类型，驱动中一般只有这一种类型
long has_lock = has_wake_lock_locked(type);
if (has_lock > 0) {
if (debug_mask & DEBUG_EXPIRE)
pr_info("wake_unlock: %s, start expire timer, "
"%ld\n", lock->name, has_lock);
mod_timer(&expire_timer, jiffies + has_lock);
} else {
if (del_timer(&expire_timer))
if (debug_mask & DEBUG_EXPIRE)
pr_info("wake_unlock: %s, stop expire "
"timer\n", lock->name);
if (has_lock == 0)//如果没有锁了，要进入标准Linux的休眠机制了，咱们接着往下跟
queue_work(suspend_work_queue, &suspend_work);
}
if (lock == &main_wake_lock) {
if (debug_mask & DEBUG_SUSPEND)
print_active_locks(WAKE_LOCK_SUSPEND);
#ifdef CONFIG_WAKELOCK_STAT
update_sleep_wait_stats_locked(0);
#endif
}
}
spin_unlock_irqrestore(&list_lock, irqflags);
}
EXPORT_SYMBOL(wake_unlock);

这里就是进入标准Linux的休眠的地方了

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static void suspend(struct work_struct *work)
{
int ret;
int entry_event_num;
struct timespec ts_entry, ts_exit;

if (has_wake_lock(WAKE_LOCK_SUSPEND)) {
if (debug_mask & DEBUG_SUSPEND)
pr_info("suspend: abort suspend\n");
return;
}

entry_event_num = current_event_num;
sys_sync();
if (debug_mask & DEBUG_SUSPEND)
pr_info("suspend: enter suspend\n");
getnstimeofday(&ts_entry);
ret = pm_suspend(requested_suspend_state);//这里是关键点
getnstimeofday(&ts_exit);

if (debug_mask & DEBUG_EXIT_SUSPEND) {
struct rtc_time tm;
rtc_time_to_tm(ts_exit.tv_sec, &tm);
pr_info("suspend: exit suspend, ret = %d "
"(%d-%02d-%02d %02d:%02d:%02d.%09lu UTC)\n", ret,
tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
tm.tm_hour, tm.tm_min, tm.tm_sec, ts_exit.tv_nsec);
}

if (ts_exit.tv_sec - ts_entry.tv_sec <= 1) {
++suspend_short_count;

if (suspend_short_count == SUSPEND_BACKOFF_THRESHOLD) {
suspend_backoff();
suspend_short_count = 0;
}
} else {
suspend_short_count = 0;
}

if (current_event_num == entry_event_num) {
if (debug_mask & DEBUG_SUSPEND)
pr_info("suspend: pm_suspend returned with no event\n");
wake_lock_timeout(&unknown_wakeup, HZ / 2);
}
}
static DECLARE_WORK(suspend_work, suspend);

static void suspend(struct work_struct *work)
{
int ret;
int entry_event_num;
struct timespec ts_entry, ts_exit;

if (has_wake_lock(WAKE_LOCK_SUSPEND)) {
if (debug_mask & DEBUG_SUSPEND)
pr_info("suspend: abort suspend\n");
return;
}

entry_event_num = current_event_num;
sys_sync();
if (debug_mask & DEBUG_SUSPEND)
pr_info("suspend: enter suspend\n");
getnstimeofday(&ts_entry);
ret = pm_suspend(requested_suspend_state);//这里是关键点
getnstimeofday(&ts_exit);

if (debug_mask & DEBUG_EXIT_SUSPEND) {
struct rtc_time tm;
rtc_time_to_tm(ts_exit.tv_sec, &tm);
pr_info("suspend: exit suspend, ret = %d "
"(%d-%02d-%02d %02d:%02d:%02d.%09lu UTC)\n", ret,
tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
tm.tm_hour, tm.tm_min, tm.tm_sec, ts_exit.tv_nsec);
}

if (ts_exit.tv_sec - ts_entry.tv_sec <= 1) {
++suspend_short_count;

if (suspend_short_count == SUSPEND_BACKOFF_THRESHOLD) {
suspend_backoff();
suspend_short_count = 0;
}
} else {
suspend_short_count = 0;
}

if (current_event_num == entry_event_num) {
if (debug_mask & DEBUG_SUSPEND)
pr_info("suspend: pm_suspend returned with no event\n");
wake_lock_timeout(&unknown_wakeup, HZ / 2);
}
}
static DECLARE_WORK(suspend_work, suspend);

[cpp]
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int pm_suspend(suspend_state_t state)
{
if (state > PM_SUSPEND_ON && state < PM_SUSPEND_MAX)
return enter_state(state);//正如你所料，开始走Linux那套休眠的流程了
return -EINVAL;
}
EXPORT_SYMBOL(pm_suspend);

int pm_suspend(suspend_state_t state)
{
if (state > PM_SUSPEND_ON && state < PM_SUSPEND_MAX)
return enter_state(state);//正如你所料，开始走Linux那套休眠的流程了
return -EINVAL;
}
EXPORT_SYMBOL(pm_suspend);

唤醒相关的代码就不贴 了，跟休眠类似的。
下面讲下驱动中如何使用wake_lock和early_suspend，总的来说，还是挺简单的

比如在设备probe的时候做如下操作

struct early_suspend early_suspend;

early_suspend.level = EARLY_SUSPEND_LEVEL_BLANK_SCREEN + 1; //等级，等级大小和suspend顺序一致，和resume顺序相反

early_suspend.suspend = xxx_early_suspend;//指定函数指针，需自己实现

early_suspend.resume = xxx_late_resume;

register_early_suspend(&early_suspend);//注册进核心，也就是加入刚才early_suspend_handlers那个链表

struct wake_lock chrg_lock;

wake_lock_init(&chrg_lock, WAKE_LOCK_SUSPEND, "xxx_wake_lock");//初始化类型为WAKE_LOCK_SUSPEND的wake_lock锁

#ifdef CONFIG_HAS_EARLYSUSPEND

static void xxx_early_suspend(struct early_suspend *h)

{

....

wake_lock(&chrg_lock);

....

}

static void xxx_late_resume(struct early_suspend *h)

{

.....

wake_unlock(&chrg_lock);

....

}

#endif