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。
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_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);
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);
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。
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。
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。
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; }
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); }
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; 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); }
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。