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android自动亮度失效问题调查_android11自动调节亮度开关没作用

作者：IT小白 | 2024-05-29 15:51:16

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android11自动调节亮度开关没作用

一. 问题描述

1.1 现象

      手机自动亮度失效，调节亮度条屏幕闪烁

1.2 JIRA

 

1.3 结论

    1.android.hardware.light@2.0-service转换亮度值出问题，导致调节屏幕亮度异常

    2.kernel设置的最大亮度值有问题，导致无法调大最大亮度

 

二. 问题分析

2.1 基础学习

在分析之前我们得大概知道自动亮度的流程整个流程，设置亮度主要通过slpi, android.hardware.sensors@1.0-service,system_server,android.hardware.light@2.0-service,kernel来五部分来共同完成。

1.slpi部分，这部分主要是光感循环读取数据，然后通过pb_send_sensor_stream_event/pb_send_event将数据发生给子系统，子系统最后会通过qmi接口将数据传给android.hardware.sensors@1.0-service。

2.android.hardware.sensors@1.0-service拿到数据后会继续传递给system_server. 这部分的具体传递过程这里就不说了，可以看一下我以前画的流程图：https://blog.csdn.net/aa787282301/article/details/84665319。

3.System_server是拿到sensor 传递过来的lux数据后会进行一系列的计算，然后得出当前的亮度值，传递给android.hardware.light@2.0-service进程。

4.android.hardware.light@2.0-service进程会把亮度值写到kernel的brightnes设备节点。

5.kernel拿到亮度值后，就去改变屏幕的亮度。

 

 

2.2 详细分析

2.2.1 闪烁问题分析

有了2.1的知识基础后我们也分进程来排查问题就好了：

1.slpi的排查可以直接在上传数据的时候打印出对应的lux值，然后看看是否符合预期，例如：

  1. TCS3701_SPRINTF(LOW, sns_fw_printf, "TCS3701 pb_send_sensor_stream_event: lux: %f\n", report_data[0]);
  2. pb_send_sensor_stream_event(instance,
  3.     &state->als_info.als_suid,
  4.     sns_get_system_time(),
  5.     SNS_STD_SENSOR_MSGID_SNS_STD_SENSOR_EVENT,
  6.     SNS_STD_SENSOR_SAMPLE_STATUS_ACCURACY_HIGH,
  7.     report_data,
  8.     ALS_EVENT_SIZE,
  9.     state->encoded_als_event_len);

然后我们直接用qxdm来看lux值是不是符合预期的，如果lux值是正确的，那我们就继续看其他进程。本节说的问题并不是tcs3701数据采集有问题，这里就不详细分析了。

2.android.hardware.sensors@1.0-service进程拿到slpi的数据后不会进过特别多的处理，会继续传递给system_server，一般情况下不会有问题。

3.system_server拿到值lux值后会做比较多的处理，过程比较复杂，我们直接看到最后，就是它要设置的亮度值：

  1. private void setDisplayBrightness(int brightness) {
  2.     if (DEBUG) {
  3.         Slog.d(TAG, "setDisplayBrightness("
  4.                 + "id=" + displayId + ", brightness=" + brightness + ")");
  5.     }
  6.  
  7.     Trace.traceBegin(Trace.TRACE_TAG_POWER, "setDisplayBrightness("
  8.             + "id=" + displayId + ", brightness=" + brightness + ")");
  9.     try {
  10.         mBacklight.setBrightness(brightness);
  11.         Trace.traceCounter(Trace.TRACE_TAG_POWER,
  12.                 "ScreenBrightness", brightness);
  13.     } finally {
  14.         Trace.traceEnd(Trace.TRACE_TAG_POWER);
  15.     }
  16. }

这里是通过mBacklight.setBrightness(brightness)来进行设置亮度，我们将DEBUG改为true,然后用手电筒照射手机，看看这里的日志是否正常：

  1. 01-01 00:06:47.649  1517  2429 D LocalDisplayAdapter: setDisplayBrightness(id=0, brightness=95)
  2. 01-01 00:06:47.679  1517  2429 D LocalDisplayAdapter: setDisplayBrightness(id=0, brightness=81)
  3. 01-01 00:06:47.699  1517  2429 D LocalDisplayAdapter: setDisplayBrightness(id=0, brightness=61)
  4. 01-01 00:06:47.726  1517  2429 D LocalDisplayAdapter: setDisplayBrightness(id=0, brightness=52)
  5. 01-01 00:06:47.743  1517  2429 D LocalDisplayAdapter: setDisplayBrightness(id=0, brightness=43)
  6. 01-01 00:06:47.770  1517  2429 D LocalDisplayAdapter: setDisplayBrightness(id=0, brightness=36)
  7. 01-01 00:06:47.816  1517  2429 D LocalDisplayAdapter: setDisplayBrightness(id=0, brightness=30)
  8. 01-01 00:06:47.836  1517  2429 D LocalDisplayAdapter: setDisplayBrightness(id=0, brightness=28)
  9. 01-01 00:06:47.863  1517  2429 D LocalDisplayAdapter: setDisplayBrightness(id=0, brightness=27)
  10. 01-01 00:06:47.876  1517  2429 D LocalDisplayAdapter: setDisplayBrightness(id=0, brightness=26)
  11. 01-01 00:06:47.942  1517  2429 D LocalDisplayAdapter: setDisplayBrightness(id=0, brightness=27)
  12. 01-01 00:06:47.963  1517  2429 D LocalDisplayAdapter: setDisplayBrightness(id=0, brightness=30)
  13. 01-01 00:06:47.984  1517  2429 D LocalDisplayAdapter: setDisplayBrightness(id=0, brightness=41)
  14. 01-01 00:06:48.005  1517  2429 D LocalDisplayAdapter: setDisplayBrightness(id=0, brightness=64)
  15. 01-01 00:06:48.027  1517  2429 D LocalDisplayAdapter: setDisplayBrightness(id=0, brightness=100)
  16. 01-01 00:06:48.058  1517  2429 D LocalDisplayAdapter: setDisplayBrightness(id=0, brightness=177)
  17. 01-01 00:06:48.082  1517  2429 D LocalDisplayAdapter: setDisplayBrightness(id=0, brightness=203)
  18. 01-01 00:06:48.099  1517  2429 D LocalDisplayAdapter: setDisplayBrightness(id=0, brightness=233)
  19. 01-01 00:06:48.122  1517  2429 D LocalDisplayAdapter: setDisplayBrightness(id=0, brightness=287)
  20. 01-01 00:06:48.146  1517  2429 D LocalDisplayAdapter: setDisplayBrightness(id=0, brightness=347)
  21. 01-01 00:06:48.161  1517  2429 D LocalDisplayAdapter: setDisplayBrightness(id=0, brightness=413)
  22. 01-01 00:06:48.182  1517  2429 D LocalDisplayAdapter: setDisplayBrightness(id=0, brightness=513)
  23. 01-01 00:06:48.202  1517  2429 D LocalDisplayAdapter: setDisplayBrightness(id=0, brightness=632)
  24. 01-01 00:06:48.223  1517  2429 D LocalDisplayAdapter: setDisplayBrightness(id=0, brightness=792)
  25. 01-01 00:06:48.248  1517  2429 D LocalDisplayAdapter: setDisplayBrightness(id=0, brightness=886)
  26. 01-01 00:06:48.281  1517  2429 D LocalDisplayAdapter: setDisplayBrightness(id=0, brightness=1237)
  27. 01-01 00:06:48.311  1517  2429 D LocalDisplayAdapter: setDisplayBrightness(id=0, brightness=1611)
  28. 01-01 00:06:48.348  1517  2429 D LocalDisplayAdapter: setDisplayBrightness(id=0, brightness=1956)
  29. 01-01 00:06:48.378  1517  2429 D LocalDisplayAdapter: setDisplayBrightness(id=0, brightness=2047)

从日志中我们能看到，亮度值随着亮度增加而增大，所以system_server的代码走到mBacklight.setBrightness(brightness)时还是正常的，我们继续往后排查。

 

4.system_server将要设置的亮度值继续传递给android.hardware.light@2.0-service进程，android.hardware.light@2.0-service进程最后会打开对应的设备节点，然后把亮度值写进去，具体代码如下：

  1. char const*const LCD_FILE
  2.         = "/sys/class/leds/lcd-backlight/brightness";
  3.  
  4. char const*const LCD_FILE2
  5.         = "/sys/class/backlight/panel0-backlight/brightness";
  6.  
  7. char const*const BUTTON_FILE
  8.         = "/sys/class/leds/button-backlight/brightness";
  9.  
  10. char const*const PERSISTENCE_FILE
  11.         = "/sys/class/graphics/fb0/msm_fb_persist_mode";
  12.         
  13.         ......
  14.         
  15. static int
  16. set_light_backlight(struct light_device_t* dev,
  17.         struct light_state_t const* state)
  18. {
  19.     int err = 0;
  20.  
  21. #ifdef USE_AOSP_BACKLIGHT_SOLUTION
  22.     int brightness = 0;
  23.     if(rgb_to_brightness(state) == 0) {
  24.         brightness = 0;
  25.     } else {
  26.         ALOGE("set_light_backlight state->color is %d\n", state->color);
  27.         brightness = (rgb_to_brightness(state)+1)* backlight_conversion;
  28.         ALOGE("%s: brightness is %d\n", __FUNCTION__, brightness);
  29.     }
  30. #else
  31.     int brightness = state->color & 0xfff;
  32. #endif
  33.  
  34.     unsigned int lpEnabled =
  35.         state->brightnessMode == BRIGHTNESS_MODE_LOW_PERSISTENCE;
  36.     if(!dev) {
  37.         return -1;
  38.     }
  39.  
  40.     pthread_mutex_lock(&g_lock);
  41.     // Toggle low persistence mode state
  42.     bool persistence_mode = ((g_last_backlight_mode != state->brightnessMode && lpEnabled) ||
  43.                             (!lpEnabled &&
  44.                             g_last_backlight_mode == BRIGHTNESS_MODE_LOW_PERSISTENCE));
  45.     bool cannot_handle_persistence = !g_has_persistence_node && persistence_mode;
  46.     if (g_has_persistence_node) {
  47.         if (persistence_mode) {
  48.             if ((err = write_int(PERSISTENCE_FILE, lpEnabled)) != 0) {
  49.                 ALOGE("%s: Failed to write to %s: %s\n", __FUNCTION__,
  50.                        PERSISTENCE_FILE, strerror(errno));
  51.             }
  52.             if (lpEnabled != 0) {
  53.                 brightness = DEFAULT_LOW_PERSISTENCE_MODE_BRIGHTNESS;
  54.             }
  55.         }
  56.         g_last_backlight_mode = state->brightnessMode;
  57.     }
  58.  
  59.     if (!err) {
  60.         if (!access(LCD_FILE, F_OK)) {
  61.             err = write_int(LCD_FILE, brightness);
  62.         } else {
  63.             ALOGE("%s: pzc write to %s: %d\n", __FUNCTION__,
  64.                        LCD_FILE2, brightness);
  65.             err = write_int(LCD_FILE2, brightness);
  66.         }
  67.     }
  68.  
  69.     pthread_mutex_unlock(&g_lock);
  70.     return cannot_handle_persistence ? -ENOSYS : err;
  71. }

上层更新亮度值就是往/sys/class/backlight/panel0-backlight/brightness设备节点写值，调用的write_int方法，我在代码里加了一些日志，编译出so后push进手机：

  1. pzc@pzc-OptiPlex-7050:~/code/hardware/qcom/display/liblight$ mm
  2. pzc@pzc-OptiPlex-7050:cd ~/code/out/target/product/xxx/vendor/lib64/hw
  3. pzc@pzc-OptiPlex-7050:~/code/out/target/product/xxx/vendor/lib64/hw$ adb root
  4. restarting adbd as root
  5. pzc@pzc-OptiPlex-7050:~/code/out/target/product/xxx/vendor/lib64/hw$ 
  6. pzc@pzc-OptiPlex-7050:~/code/out/target/product/xxx/vendor/lib64/hw$ adb remount
  7. remount succeeded
  8. pzc@pzc-OptiPlex-7050:~/code/out/target/product/xxx/vendor/lib64/hw$ adb push lights.sm6150.so  /vendor/lib64/hw/
  9. lights.sm6150.so: 1 file pushed. 2.0 MB/s (68784 bytes in 0.032s)
  10. pzc@pzc-OptiPlex-7050:~/code/out/target/product/xxx/vendor/lib64/hw$ adb reboot

然后我们查看相应的日志：

  1. 130|xxx:/ $ ps -ef  | grep light
  2. system         675     1 1 23:59:52 ?     00:00:01 android.hardware.light@2.0-service
  3. shell         5204  3668 5 00:02:15 pts/0 00:00:00 grep light
  4. xxx:/ $ logcat | grep 675
  5. 01-01 00:01:32.647   675   675 E qdlights: set_light_backlight state->color is 1360
  6. 01-01 00:01:32.647   675   675 E qdlights: set_light_backlight: brightness is 96
  7. 01-01 00:01:32.647   675   675 E qdlights: set_light_backlight: pzc write to /sys/class/backlight/panel0-backlight/brightness: 96
  8. 01-01 00:01:32.664   675   675 E qdlights: set_light_backlight state->color is 1420
  9. 01-01 00:01:32.664   675   675 E qdlights: set_light_backlight: brightness is 152
  10. 01-01 00:01:32.664   675   675 E qdlights: set_light_backlight: pzc write to /sys/class/backlight/panel0-backlight/brightness: 152
  11. 01-01 00:01:32.681   675   675 E qdlights: set_light_backlight state->color is 1487
  12. 01-01 00:01:32.681   675   675 E qdlights: set_light_backlight: brightness is 216
  13. 01-01 00:01:32.681   675   675 E qdlights: set_light_backlight: pzc write to /sys/class/backlight/panel0-backlight/brightness: 216
  14. 01-01 00:01:32.698   675   675 E qdlights: set_light_backlight state->color is 1558
  15. 01-01 00:01:32.698   675   675 E qdlights: set_light_backlight: brightness is 56
  16. 01-01 00:01:32.698   675   675 E qdlights: set_light_backlight: pzc write to /sys/class/backlight/panel0-backlight/brightness: 56
  17. 01-01 00:01:32.714   675   675 E qdlights: set_light_backlight state->color is 1621
  18. 01-01 00:01:32.714   675   675 E qdlights: set_light_backlight: brightness is 112
  19. 01-01 00:01:32.714   675   675 E qdlights: set_light_backlight: pzc write to /sys/class/backlight/panel0-backlight/brightness: 112
  20. 01-01 00:01:32.730   675   675 E qdlights: set_light_backlight state->color is 1687
  21. 01-01 00:01:32.730   675   675 E qdlights: set_light_backlight: brightness is 168
  22. 01-01 00:01:32.730   675   675 E qdlights: set_light_backlight: pzc write to /sys/class/backlight/panel0-backlight/brightness: 168
  23. 01-01 00:01:32.747   675   675 E qdlights: set_light_backlight state->color is 1745
  24. 01-01 00:01:32.747   675   675 E qdlights: set_light_backlight: brightness is 224
  25. 01-01 00:01:32.747   675   675 E qdlights: set_light_backlight: pzc write to /sys/class/backlight/panel0-backlight/brightness: 224
  26. 01-01 00:01:32.763   675   675 E qdlights: set_light_backlight state->color is 1795
  27. 01-01 00:01:32.763   675   675 E qdlights: set_light_backlight: brightness is 40
  28. 01-01 00:01:32.764   675   675 E qdlights: set_light_backlight: pzc write to /sys/class/backlight/panel0-backlight/brightness: 40
  29. 01-01 00:01:32.780   675   675 E qdlights: set_light_backlight state->color is 1851
  30. 01-01 00:01:32.780   675   675 E qdlights: set_light_backlight: brightness is 88
  31. 01-01 00:01:32.780   675   675 E qdlights: set_light_backlight: pzc write to /sys/class/backlight/panel0-backlight/brightness: 88
  32. 01-01 00:01:32.797   675   675 E qdlights: set_light_backlight state->color is 1903
  33. 01-01 00:01:32.798   675   675 E qdlights: set_light_backlight: brightness is 136
  34. 01-01 00:01:32.798   675   675 E qdlights: set_light_backlight: pzc write to /sys/class/backlight/panel0-backlight/brightness: 136
  35. 01-01 00:01:32.813   675   675 E qdlights: set_light_backlight state->color is 1962
  36. 01-01 00:01:32.813   675   675 E qdlights: set_light_backlight: brightness is 192
  37. 01-01 00:01:32.813   675   675 E qdlights: set_light_backlight: pzc write to /sys/class/backlight/panel0-backlight/brightness: 192
  38. 01-01 00:01:32.831   675   675 E qdlights: set_light_backlight state->color is 2018
  39. 01-01 00:01:32.831   675   675 E qdlights: set_light_backlight: brightness is 240
  40. 01-01 00:01:32.831   675   675 E qdlights: set_light_backlight: pzc write to /sys/class/backlight/panel0-backlight/brightness: 240

从这日志我们能发现state->color的值是正确的，计算过后的brightness错误了，在亮度变大的过程中brightness由0增加，到达250多又从0开始。从日志中我们就得到了和测试反馈一样的闪屏现象。

  1. #ifdef USE_AOSP_BACKLIGHT_SOLUTION
  2.     int brightness = 0;
  3.     if(rgb_to_brightness(state) == 0) {
  4.         brightness = 0;
  5.     } else {
  6.         ALOGE("set_light_backlight state->color is %d\n", state->color);
  7.         brightness = (rgb_to_brightness(state)+1)* backlight_conversion;
  8.         ALOGE("%s: brightness is %d\n", __FUNCTION__, brightness);
  9.     }
  10. #else
  11.     int brightness = state->color & 0xfff;
  12. #endif

继续看能发现有个宏定义，在定义了USE_AOSP_BACKLIGHT_SOLUTION的情况下数据会经过计算，反之就&2048（屏幕亮度的最大值）。

因为这是我们自己加的代码就不详细展开了，这个宏定义是为了区分原生版本和MIUI版本的，原生版本的最大亮度值是256,MIUI版本是2048，因为这个宏被定义了导致计算出错，最终导致屏幕闪烁，解决办法只需要在我们的版本中去掉这个宏定义，然后就能解决这个闪烁的问题了。

2.2.1 亮度调不动问题分析

再解决闪烁问题之后，接着又遇到一个新问题，我们调屏幕亮度的时候调到一半就调不动了。。。。然后继续看相关日志，这次发现亮度值确实已经正确的写进了/sys/class/backlight/panel0-backlight/brightness设备节点了，但是亮度只能调节一段范围，继续打印日志分析：

  1. int dsi_panel_set_backlight(struct dsi_panel *panel, u32 bl_lvl)
  2. {
  3. ......
  4. 	pr_debug("backlight type:%d lvl:%d\n", bl->type, bl_lvl);
  5.  
  6. 	if (0 == bl_lvl)
  7. 		dsi_panel_tx_cmd_set(panel, DSI_CMD_SET_DISP_DIMMINGOFF);
  8.  
  9. ......
  10. 	panel->last_bl_lvl = bl_lvl;
  11. 	return rc;
  12. }

我们能在kernel设置亮度的流程发现有打印日志的地方，我们把日志打印出来看一下：

  1. xxx:/ # echo "func dsi_panel_set_backlight +tp" > /d/dynamic_debug/control 
  2. xxx:/ # dmesg | grep dsi_panel_set_backlight  
  3. [   63.406678] [689] msm-dsi-panel:[dsi_panel_set_backlight:708] backlight type:2 lvl:208
  4. [   63.506478] [689] msm-dsi-panel:[dsi_panel_set_backlight:708] backlight type:2 lvl:216
  5. [   63.524899] [689] msm-dsi-panel:[dsi_panel_set_backlight:708] backlight type:2 lvl:224
  6. [   63.539299] [689] msm-dsi-panel:[dsi_panel_set_backlight:708] backlight type:2 lvl:240
  7. [   63.557805] [689] msm-dsi-panel:[dsi_panel_set_backlight:708] backlight type:2 lvl:264
  8. [   63.573974] [689] msm-dsi-panel:[dsi_panel_set_backlight:708] backlight type:2 lvl:288
  9. [   63.592018] [689] msm-dsi-panel:[dsi_panel_set_backlight:708] backlight type:2 lvl:313
  10. [   63.608887] [689] msm-dsi-panel:[dsi_panel_set_backlight:708] backlight type:2 lvl:345
  11. ......
  12. [   65.219863] [689] msm-dsi-panel:[dsi_panel_set_backlight:708] backlight type:2 lvl:2047
  13. [   65.237156] [689] msm-dsi-panel:[dsi_panel_set_backlight:708] backlight type:2 lvl:2047
  14. [   65.256433] [689] msm-dsi-panel:[dsi_panel_set_backlight:708] backlight type:2 lvl:2047
  15. [   65.271771] [689] msm-dsi-panel:[dsi_panel_set_backlight:708] backlight type:2 lvl:2047
  16. [   65.289537] [689] msm-dsi-panel:[dsi_panel_set_backlight:708] backlight type:2 lvl:2047
  17. [   65.305404] [689] msm-dsi-panel:[dsi_panel_set_backlight:708] backlight type:2 lvl:2047

我们能发现当我们调节亮度条时，亮度调只调了一半（上层设置的值还没到2047），kernel中对应的亮度值已经到了2047了，所以我们得看看这之前亮度值发生了什么变化，直接找到写brightness节点的入口方法：

  1. static ssize_t brightness_store(struct device *dev,
  2.         struct device_attribute *attr, const char *buf, size_t count)
  3. {
  4.     int rc;
  5.     struct backlight_device *bd = to_backlight_device(dev);
  6.     unsigned long brightness;
  7.  
  8.     rc = kstrtoul(buf, 0, &brightness);
  9.     if (rc)
  10.         return rc;
  11.  
  12.     bd->usr_brightness_req = brightness;
  13.  
  14.     pr_err("pzc brightness_store1 buf:%s\n", buf);
  15.     pr_err("pzc brightness_store1 brightness:%lu\n", brightness);
  16.  
  17.     pr_err("pzc brightness_store1 bd->thermal_brightness_limit:%lu\n", bd->thermal_brightness_limit);
  18.     pr_err("pzc brightness_store1 bd->usr_brightness_req:%lu\n", bd->usr_brightness_req);
  19.  
  20.     brightness = (brightness <= bd->thermal_brightness_limit) ?
  21.                 bd->usr_brightness_req :
  22.                 bd->thermal_brightness_limit;
  23.     pr_err("pzc brightness_store2 brightness:%lu\n", brightness);
  24.  
  25.     rc = backlight_device_set_brightness(bd, brightness);
  26.  
  27.     return rc ? rc : count;
  28. }

这里我们能看到brightness 会和bd->thermal_brightness_limit做对比，取小的值。看着就很符合我们的日志现象，直接加个日志看看吧：

  1. [ 2513.153084] backlight: pzc brightness_store1 buf:405\x0a
  2. [ 2513.153087] backlight: pzc brightness_store1 brightness:405
  3. [ 2513.153088] backlight: pzc brightness_store1 bd->thermal_brightness_limit:255
  4. [ 2513.153089] backlight: pzc brightness_store1 bd->usr_brightness_req:405
  5. [ 2513.153090] backlight: pzc brightness_store2 brightness:255
  6. [ 2513.153092] backlight: pzc backlight_device_set_brightness 255

日志中我们能看到bd->thermal_brightness_limit就是255，这里限制了设置亮度的最大值为255，那我们接着找看看这个bd->thermal_brightness_limit的值在哪里被设置的：

  1. static int bd_cdev_set_cur_brightness(struct thermal_cooling_device *cdev,
  2.                     unsigned long state)
  3. {
  4.     struct backlight_device *bd = (struct backlight_device *)cdev->devdata;
  5.     int brightness_lvl;
  6.  
  7.     dump_stack();
  8.     pr_err("pzc1 bd_cdev_set_cur_brightness bd->props.max_brightness:%lu\n", bd->props.max_brightness);
  9.     pr_err("pzc1 bd_cdev_set_cur_brightness state:%lu\n", state);
  10.     brightness_lvl = bd->props.max_brightness - state;
  11.     if (brightness_lvl == bd->thermal_brightness_limit)
  12.         return 0;
  13.  
  14.     pr_err("pzc1 brightness_store1 brightness_lvl:%lu\n", brightness_lvl);
  15.  
  16.     bd->thermal_brightness_limit = brightness_lvl;
  17.     brightness_lvl = (bd->usr_brightness_req
  18.                 <= bd->thermal_brightness_limit) ?
  19.                 bd->usr_brightness_req :
  20.                 bd->thermal_brightness_limit;
  21.     backlight_device_set_brightness(bd, brightness_lvl);
  22.  
  23.     return 0;
  24. }

这里的bd->thermal_brightness_limit = bd->props.max_brightness - state，打印日志后可以看到bd->props.max_brightness =255，state=0，我们接着看看bd->props.max_brightness在哪里被设置的：

  1. static int sde_backlight_setup(struct sde_connector *c_conn,
  2. 					struct drm_device *dev)
  3. {
  4. ......
  5. 	bl_config = &display->panel->bl_config;
  6. 	props.max_brightness = bl_config->brightness_max_level;
  7. 	props.brightness = bl_config->brightness_max_level;
  8. ......
  9.  
  10. 	return 0;
  11. }

props.max_brightness又等于bl_config->brightness_max_level，继续看看brightness_max_level在哪里被设置的：

  1. static int dsi_panel_parse_bl_config(struct dsi_panel *panel)
  2. {
  3. ......
  4.     rc = utils->read_u32(utils->data, "qcom,mdss-brightness-max-level",
  5. 	if (rc) {
  6. 		pr_debug("[%s] brigheness-max-level unspecified, defaulting to 255\n",
  7. 			 panel->name);
  8. 		panel->bl_config.brightness_max_level = 255;
  9. 	} else {
  10. 		panel->bl_config.brightness_max_level = val;
  11. 	}
  12. ......
  13. error:
  14. 	return rc;
  15. }

到了这里我们最终找到了设置最大亮度的地方，是在dtbo文件中进行了配置：

qcom,mdss-brightness-max-level = <255>;

我们将这里修改为2047:

qcom,mdss-brightness-max-level = <2047>;

打包后再进行测试，自动亮度和亮度调节都恢复正常了。

三. 总结

这里一共出现了两个问题，一个是上层亮度转换出错导致了亮度值设置异常，另一个是kernel默认的最大亮度值设置错误，导致屏幕无法调节到真正的最大亮度值。在分析问题的时候可以把问题分不同的层级逐一排查缩小范围，然后再针对某个点单独进行的深入分析，能够提高不少效率。

 

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