android 休眠唤醒机制分析(二) — early_suspend - android

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。

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",};

但在Android中一般只支持"on"和"mem"，其中"on"为唤醒设备，"mem"为休眠设备。/sys/power/state节点的读写操作如下：

static ssize_t state_show(struct kobject *kobj, struct kobj_attribute *attr,  char *buf){char *s = buf;#ifdef CONFIG_SUSPENDint 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_HIBERNATIONs += sprintf(s, "%s\n", "disk");#elseif (s != buf)/* convert the last space to a newline */*(s-1) = '\n';#endifreturn (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_EARLYSUSPENDsuspend_state_t state = PM_SUSPEND_ON;#elsesuspend_state_t state = PM_SUSPEND_STANDBY;#endifconst char * const *s;#endifchar *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_SUSPENDfor (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_EARLYSUSPENDif (state == PM_SUSPEND_ON || valid_state(state)) {error = 0;request_suspend_state(state);  // 请求进入android的休眠流程}#elseerror = 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#endifNULL,};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_EARLYSUSPENDstruct 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);

其中register_early_suspend()用于注册，unregister_early_suspend用于注销；一般early_suspend的使用方式如下：

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);

设置好suspend和resume接口，定义优先等级，然后注册结构即可。

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;

初始化了一个链表early_suspend_handlers用于管理early_suspend，还定义读写链表用到的互斥体；另外还声明了3个工作队列，分别用于缓存同步、浅度休眠和唤醒；还声明了early_suspend操作的3个状态。
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);

注册的流程比较简单，首先遍历链表，依次比较每个节点的优先等级，如果遇到优先等级比新节点优先等级高则跳出，然后将新节点加入优先等级较高的节点前面，这样就确保了链表是优先等级低在前高在后的顺序；在将节点加入链表后查看当前状态是否为浅度休眠完成状态，如果是则执行handler的suspend函数。

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);

注销流程则只是将节点从链表中移除。
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);}

函数首先打印出当前状态变化的log，然后判断新状态，如果是休眠状态则置位SUSPEND_REQUESTED标志，然后将同步缓存、浅度休眠工作队列加入相应的内核线程执行；如果新状态是唤醒则首先将main_wake_lock激活，然后再将浅度唤醒工作队列加入内核线程执行；最后更新全局状态变量，因为提供了一个内核空间接口用于获取当前休眠唤醒状态：

// 返回系统状态值suspend_state_t get_suspend_state(void){return requested_suspend_state;}

5、early_suspend_work、late_resume_work 和early_sys_sync

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SUSPENDEDelseabort = 1;spin_unlock_irqrestore(&state_lock, irqflags);if (abort) {  // 取消early_suspendif (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);}

在suspend流程中首先判断当前状态是否为SUSPEND_REQUESTED，如果是则置位SUSPENDED标志，如果不是则取消suspend流程；然后遍历浅度休眠链表，从链表头部到尾部依次调用各节点的suspend()函数，执行完后判断当前状态是否为SUSPEND_REQUESTED_AND_SUSPENDED，如果是则释放 main_wake_lock，当前系统中如果只存在main_wake_lock这个有效锁，则会在wake_unlock()里面启动 深度休眠线程，如果还有其他其他wake_lock则保持当前状态。

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;elseabort = 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);}

在resume流程中同样首先判断当前状态是否为SUSPENDED，如果是则清除SUSPENDED标志，然后反向遍历浅度休眠链表，按照优先等级从高到低的顺序执行节点的resume()函数。

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。

android 休眠唤醒机制分析(二) — early_suspend

更多相关文章

随机推荐