android 休眠唤醒机制分析(二) — early_suspend
early_suspend是Android休眠流程的第一阶段即浅度休眠，不会受到wake_lock的阻止，一般用于关闭lcd、tp等设备为运行的应用节约电能。Android的PowerManagerService会根据用户的操作情况调整电源状态，如果需要休眠则会调用到HAL层的set_screen_state()接口，在set_screen_state()中会向/sys/power/state节点写入"mem"值让驱动层开始进入休眠流程。
3、register_early_suspend 和 unregister_early_suspend
4、request_suspend_state
一、休眠唤醒机制及其用户空间接口
Linux系统支持如下休眠唤醒等级
const char *const pm_states[PM_SUSPEND_MAX] = {
#ifdef CONFIG_EARLYSUSPEND
[PM_SUSPEND_ON] = "on",
#endif
[PM_SUSPEND_STANDBY] = "standby",
[PM_SUSPEND_MEM] = "mem",
};static ssize_t state_show(struct kobject *kobj, struct kobj_attribute *attr,
char *buf)
{
char *s = buf;
#ifdef CONFIG_SUSPEND
int i;
for (i = 0; i < PM_SUSPEND_MAX; i++) {
if (pm_states[i] && valid_state(i))
s += sprintf(s,"%s ", pm_states[i]); // 打印系统支持的休眠等级
}
#endif
#ifdef CONFIG_HIBERNATION
s += sprintf(s, "%s\n", "disk");
#else
if (s != buf)
/* convert the last space to a newline */
*(s-1) = '\n';
#endif
return (s - buf);
}
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); // 请求进入android的休眠流程
}
#else
error = enter_state(state); // linux的标准休眠流程
#endif
#endif
Exit:
return error ? error : n;
}
power_attr(state);其中state_show()为节点的读函数，主要打印出系统支持的休眠等级；state_store()为节点的写函数，根据参数请求休眠或者唤醒流程。节点的创建代码如下：
static struct attribute * g[] = {
&state_attr.attr, // state节点
#ifdef CONFIG_PM_TRACE
&pm_trace_attr.attr,
#endif
#if defined(CONFIG_PM_SLEEP) && defined(CONFIG_PM_DEBUG)
&pm_test_attr.attr, // pm_test节点
#endif
#ifdef CONFIG_USER_WAKELOCK
&wake_lock_attr.attr, // wake_lock节点
&wake_unlock_attr.attr, // wake_unlock节点
#endif
NULL,
};
static struct attribute_group attr_group = {
.attrs = g,
};
static int __init pm_init(void)
{
int error = pm_start_workqueue();
if (error)
return error;
power_kobj = kobject_create_and_add("power", NULL); // 创建power节点
if (!power_kobj)
return -ENOMEM;
return sysfs_create_group(power_kobj, &attr_group); // 创建一组属性节点
}
core_initcall(pm_init);二、early_suspend 实现
1、early_suspend 定义、接口及其用法
enum {
EARLY_SUSPEND_LEVEL_BLANK_SCREEN = 50,
EARLY_SUSPEND_LEVEL_STOP_DRAWING = 100,
EARLY_SUSPEND_LEVEL_DISABLE_FB = 150,
};
struct early_suspend {
#ifdef CONFIG_HAS_EARLYSUSPEND
struct list_head link; // 链表节点
int level; // 优先等级
void (*suspend)(struct early_suspend *h);
void (*resume)(struct early_suspend *h);
#endif
};可以看到early_suspend由两个函数指针、链表节点、优先等级组成；内核默认定义了3个优先等级，在suspend的时候先执行优先等级低的handler，在resume的时候则先执行等级高的handler，用户可以定义自己的优先等级；early_suspend向内核空间提供了2个接口用于注册和注销handler：
void register_early_suspend(struct early_suspend *handler);
void unregister_early_suspend(struct early_suspend *handler);ts->earlysuspend.suspend = sitronix_i2c_suspend_early;
ts->earlysuspend.resume = sitronix_i2c_resume_late;
ts->earlysuspend.level = EARLY_SUSPEND_LEVEL_BLANK_SCREEN;
register_early_suspend(&ts->earlysuspend);2、初始化信息
我们看一下early_suspend需要用到的一些数据：
static DEFINE_MUTEX(early_suspend_lock);
static LIST_HEAD(early_suspend_handlers); // 初始化浅度休眠链表
// 声明3个工作队列用于同步、浅度休眠和唤醒
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, // 当前正在请求浅度休眠
SUSPENDED = 0x2, // 浅度休眠完成
SUSPEND_REQUESTED_AND_SUSPENDED = SUSPEND_REQUESTED | SUSPENDED,
};
static int state;3、register_early_suspend 和 unregister_early_suspend
void register_early_suspend(struct early_suspend *handler)
{
struct list_head *pos;
mutex_lock(&early_suspend_lock);
// 遍历浅度休眠链表
list_for_each(pos, &early_suspend_handlers) {
struct early_suspend *e;
e = list_entry(pos, struct early_suspend, link);
// 判断当前节点的优先等级是否大于handler的优先等级
// 以此决定handler在链表中的顺序
if (e->level > handler->level)
break;
}
// 将handler加入当前节点之前,优先等级越低越靠前
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);4、request_suspend_state
前面我们看到用户空间在写/sys/power/state节点的时候会执行request_suspend_state()函数，该函数代码如下：
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;
// 打印当前状态
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);
}
// 如果新状态是休眠状态
if (!old_sleep && new_state != PM_SUSPEND_ON) {
state |= SUSPEND_REQUESTED;
pr_info("sys_sync_work_queue early_sys_sync_work.\n");
// 执行缓存同步与浅度休眠的工作队列
queue_work(sys_sync_work_queue, &early_sys_sync_work);
queue_work(suspend_work_queue, &early_suspend_work);
} else if (old_sleep && new_state == PM_SUSPEND_ON) {
// 如果新状态是唤醒状态
state &= ~SUSPEND_REQUESTED;
// 激活内核锁
wake_lock(&main_wake_lock);
// 执行浅度唤醒的工作队列
queue_work(suspend_work_queue, &late_resume_work);
}
// 更新全局状态
requested_suspend_state = new_state;
spin_unlock_irqrestore(&state_lock, irqflags);
}// 返回系统状态值
suspend_state_t get_suspend_state(void)
{
return requested_suspend_state;
}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) // 判断当前状态是否在请求浅度休眠
state |= SUSPENDED; // 如果是则置位SUSPENDED
else
abort = 1;
spin_unlock_irqrestore(&state_lock, irqflags);
if (abort) { // 取消early_suspend
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");
// 遍历浅度休眠链表并执行其中所有suspend函数
// 执行顺序根据优先等级而定,等级越低越先执行
list_for_each_entry(pos, &early_suspend_handlers, link) {
if (pos->suspend != NULL)
pos->suspend(pos);
}
mutex_unlock(&early_suspend_lock);
if (debug_mask & DEBUG_SUSPEND)
pr_info("early_suspend: sync\n");
/* Remove sys_sync from early_suspend, and use work queue to complete sys_sync */
//sys_sync();
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 = 0;
mutex_lock(&early_suspend_lock);
spin_lock_irqsave(&state_lock, irqflags);
if (state == SUSPENDED) // 清除浅度休眠完成标志
state &= ~SUSPENDED;
else
abort = 1;
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");
// 反向遍历浅度休眠链表并执行其中所有resume函数
// 执行顺序根据优先等级而定,等级越高越先执行
list_for_each_entry_reverse(pos, &early_suspend_handlers, link)
if (pos->resume != NULL)
pos->resume(pos);
if (debug_mask & DEBUG_SUSPEND)
pr_info("late_resume: done\n");
abort:
mutex_unlock(&early_suspend_lock);
}static void early_sys_sync(struct work_struct *work)
{
wake_lock(&sys_sync_wake_lock);
sys_sync();
wake_unlock(&sys_sync_wake_lock);
}内核专门为缓存同步建立了一个线程，同时还创建了sys_sync_wake_lock防止在同步缓存时系统进入深度休眠。