Power键不亮屏分析方法
(1) 以下是列出的整个按键唤醒的log关键点，每条都有粗体字说明其含义以及该注意的关键字；
(2) 一条一条依次检查，直到如果发现某条log找不到，那问题就出在这个地方；
(3) 如果某个阶段的时间比较长，可能造成不亮屏的假象，可以分析亮屏时间长的原因
(4) 仅限于L之后的android版本；
kernel-Check Point【1】：kernel 上报power key[kernel log]
[53:pMIC_thread]kpd: Power Key generate, pressed=0
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Check Point【2】：上层收到按键事件[eng版本上才有此log，main_log]
11-21 16:57:31.001050 1020 1262 D WindowManager: interceptKeyTq keycode=26 ...
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Check Point【3】：PMS的wakeUp被调用[sys_log]
16:57:31.011153 1020 1262 I PowerManagerService: Waking up fROM sleep (uid 1000)...
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Check Point【4】：准备绘制界面[sys_log]
11-21 16:57:31.022639 1020 1044 I DisplayPowerController: Blocking screen on until initial contents have been drawn.
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Check Point【5】：第一个wiating for drawn表示keyguard画完，开始画window[sys_log]
11-21 16:57:31.062667 1020 1041 I WindowManager: Waiting for drawn Window{6732b98 u0 com.android.settings/com.android.settings.SubSettings}:
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check Point【6】：底层resume时间L版本 setAutoSuspend/M版本 setPowerMode【main_log】
注意：这个log出现的时间点不是固定的，要看底层resume的时间
16:57:31.436586 1020 1301 D SurfaceControl: Excessive delay in setPowerMode(): 403ms【M 版本】
15:41:07.827 911 2234 D PowerManagerService-JNI: Excessive delay in autosuspend_disable() while turning screen on: 424ms【L版本】
Check Point【7】：绘制界面完成及花费的时间[sys_log]
11-21 16:57:31.431161 1020 1044 I DisplayPowerController: Unblocked screen on after 409 ms
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Check Point【8】：上层设置背光[sys_log]
11-21 16:57:31.443164 1020 1044 D DisplayPowerState: Requesting new screen state: state=ON, backlight=211
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Check Point【9】：底层设置背光[sys_log,亮屏时间=power key到此处的时间，不一定每个版本都有此log，kernel log]
提示：如果出现此log表示屏幕已经点亮
<7>[ 553.658233] (3)[1301:PhotonicModulat][name:leds&][LED]Set Backlight directly 211 at time 4294992661, mapping level is 211
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Check Point【10】：亮屏操作完成[sys_log]
11-21 16:57:31.556750 1020 1044 D DisplayPowerController: Finished business...
学习了。