安卓系统待机一会就进入了深度睡眠，终端都没响应。信息如下：
[cpp] view plain copy ] request_suspend_state: sleep (0->3) at 175730206087 (2017-09-27 01:28:31.556133562 UTC) [ 175.738202] s3cfb_early_suspend is called [ 175.741885] (s3cfb_backlight_off, 546): LCD_PWM_OFF [ 175.756345] (s3cfb_backlight_off, 588): VGA_EN_OFF [ 175.764283] (s3cfb_backlight_off, 603): BK_VDD_OFF [ 176.004117] <<-GTP-INFO->> Esd suspended! [ 176.038412] PM: Syncing filesystems ... done. [ 176.065360] Freezing user space processes ... (elapsed 0.01 seconds) done. [ 176.086237] Freezing remaining freezable tasks ... (elapsed 0.01 seconds) done. [ 176.106202] Suspending console(s) (use no_console_suspend to debug) 从信息看来，android系统把用户空间的任务都停止掉了，wifi和触摸屏都没响应，只有点击电源键安卓系统才能唤醒。跟踪代码，发现最后一步系统电源管理进入了enter_state，从而执行了深度休眠的操作。源文件:kernel/power/suspend.c
[cpp] view plain copy int enter_state(suspend_state_t state) { int error; if (!valid_state(state)) return -ENODEV; if (!mutex_trylock(&pm_mutex)) return -EBUSY; printk(KERN_INFO "PM: Syncing filesystems ... "); sys_sync(); printk("done.\n"); pr_debug("PM: Preparing system for %s sleep\n", pm_states[state]); error = suspend_prepare(); if (error) goto Unlock; if (suspend_test(TEST_FREEZER)) goto Finish; pr_debug("PM: Entering %s sleep\n", pm_states[state]); error = suspend_devices_and_enter(state); Finish: pr_debug("PM: Finishing wakeup.\n"); suspend_finish(); Unlock: mutex_unlock(&pm_mutex); return error; } 2.分析android系统有earlysuspend和suspend两种休眠，earlysuspend是浅度睡眠，suspend是深度休眠。这个是由linux电源管理控制的，电源管理的接口是“/sys/power/state”和"/sys/power/wake_lock","/sys/power/wake_unlock"，这个是linux是否休眠和是否进入深度休眠的关键点。只有wake_lock上锁了，linux系统就不会进入深度休眠。
3.解决
从上分析可知，只要linux保持有一个唤醒锁，系统就不会进入深度休眠。那么解决问题的思路是在linux启动的时候添加一个唤醒锁就行了。在init.rc文件里面添加一个初始化项：
[cpp] view plain copy echo "PowerManagerService.noSuspend" > /sys/power/wake_lock 问题解决。参考资料：
1.Android 内核驱动——电源管理 ：http://blog.sina.com.cn/s/blog_67d955460100xlyh.html
2.Android后台的linux一直保持唤醒状态，不进入睡眠：http://www.cnblogs.com/yajing-zh/p/4891780.html
