Android LCD和键盘 背光亮度数据流分析

同时参考：linux设备模型之led子系统

1【从应用层到Framework】android LCD、键盘灯的背光亮度设置 

2   原文地址：  http://www.linuxidc.com/Linux/2011-03/33311p2.htm

 

 

亮度设置
应用设计
1.1 设置进度条范围
背光设置是在：设置->声音和显示->亮度，通过进度条来设置的。

文件：
packages/apps/Settings/src/com/Android/settings/BrightnessPreference.java

private static final int MINIMUM_BACKLIGHT = Android.os.Power.BRIGHTNESS_DIM + 10;
private static final int MAXIMUM_BACKLIGHT = Android.os.Power.BRIGHTNESS_ON;
mSeekBar.setMax(MAXIMUM_BACKLIGHT - MINIMUM_BACKLIGHT);

设置进度条的范围，BRIGHTNESS_DIM = 20  BRIGHTNESS_ON=255，它们的定义在：
frameworks/base/core/java/Android/os/Power.java
1.2 设置亮度
文件：packages/apps/Settings/src/com/Android/settings/BrightnessPreference.java

Java代码  

public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
       setMode(isChecked ? Settings.System.SCREEN_BRIGHTNESS_MODE_AUTOMATIC
                : Settings.System.SCREEN_BRIGHTNESS_MODE_MANUAL);
        if (!isChecked) {
            setBrightness(mSeekBar.getProgress() + MINIMUM_BACKLIGHT);
        }
    }

private void setBrightness(int brightness) {
        try {
            IPowerManager power = IPowerManager.Stub.asInterface(
                    ServiceManager.getService("power"));
            if (power != null) {
                power.setBacklightBrightness(brightness);
            }
        } catch (RemoteException doe) {
        }
}

由以上代码可知，brightness的范围是：20~255;代码通过服务管理器(ServiceManager)获得power服务，然后通过power服务设置亮度。
power.setBacklightBrightness的定义在：
rameworks/base/core/java/Android/os/IPowerManager.aidl.java
frameworks/base/core/java/Android/os/PowerManager.java

2， Power服务
文件：frameworks/base/core/java/Android/os/Power.java

                  /** * Brightness value for dim backlight   */ 
    public static final int BRIGHTNESS_DIM = 20; 
                  /** * Brightness value for fully on      */ 

    public static final int BRIGHTNESS_ON = 255; 

文件：frameworks/base/core/java/Android/os/PowerManager.java
Java代码  

/** * sets the brightness of the backlights (screen, keyboard, button).
      *
     * @param brightness value from 0 to 255
     *
     * {@hide}
     */

    public void setBacklightBrightness(int brightness)
    {
        try {
            mService.setBacklightBrightness(brightness);
        } catch (RemoteException e) {
           }
}

新代码起始：

framework\base\service\java\com\android\server\PowerManagerService.java
 
//PowerManagerService中定义的mButtonLight和mKeyboardLight都是键盘灯，具体使用哪一个，要看底层的平台厂商使用
0196	    private LightsService.Light mLcdLight;
0197	    private LightsService.Light mButtonLight;
0198	    private LightsService.Light mKeyboardLight;
 
2921	    public void setBacklightBrightness(int brightness) {
2922	        mContext.enforceCallingOrSelfPermission(android.Manifest.permission.DEVICE_POWER, null);
2923	        // Don't let applications turn the screen all the way off
2924	        synchronized (mLocks) {
2925	            brightness = Math.max(brightness, mScreenBrightnessDim);
                    //以下设备分别调用了LightsService.light的接口
2926	            mLcdLight.setBrightness(brightness);
2927	            mKeyboardLight.setBrightness(mKeyboardVisible ? brightness : 0);
2928	            mButtonLight.setBrightness(brightness);
2929	            long identity = Binder.clearCallingIdentity();
2930	            try {
2931	                mBatteryStats.noteScreenBrightness(brightness);
2932	            } catch (RemoteException e) {
2933	                Slog.w(TAG, "RemoteException calling noteScreenBrightness on BatteryStatsService", e);
2934	            } finally {
2935	                Binder.restoreCallingIdentity(identity);
2936	            }
2937	  
2938	            // update our animation state
2939	            synchronized (mLocks) {
2940	                mScreenBrightness.targetValue = brightness;
2941	                mScreenBrightness.jumpToTargetLocked();
2942	            }
2943	        }
2944	    }
 
framework\base\service\java\com\android\server\LightsService.java
 
066	        public void setBrightness(int brightness) {
067	            setBrightness(brightness, BRIGHTNESS_MODE_USER);
068	        }
069	  
070	        public void setBrightness(int brightness, int brightnessMode) {
071	            synchronized (this) {
072	                int color = brightness & 0x000000ff;
073	                color = 0xff000000 | (color << 16) | (color << 8) | color;
074	                setLightLocked(color, LIGHT_FLASH_NONE, 0, 0, brightnessMode);
075	            }
076	        }
 
116	        private void setLightLocked(int color, int mode, int onMS, int offMS, int brightnessMode) {
117	            if (color != mColor || mode != mMode || onMS != mOnMS || offMS != mOffMS) {
118	                mColor = color;
119	                mMode = mode;
120	                mOnMS = onMS;
121	                mOffMS = offMS;
                        //调用JNI的本地接口，mNativePointer对应具体设备，通过调用LighsService中的init接口，进一步调用init_native接口获取设备信息
122	                setLight_native(mNativePointer, mId, color, mode, onMS, offMS, brightnessMode);
123	            }
124	        }
 
framework\base\services\jni\com_android_server_LightsService.cpp
  
106	static void setLight_native(JNIEnv *env, jobject clazz, int ptr,
107	        int light, int colorARGB, int flashMode, int onMS, int offMS, int brightnessMode)
108	{
109	    Devices* devices = (Devices*)ptr;
110	    light_state_t state;
111	  
112	    if (light < 0 || light >= LIGHT_COUNT || devices->lights[light] == NULL) {
113	        return ;
114	    }
115	  
116	    memset(&state, 0, sizeof(light_state_t));
117	    state.color = colorARGB;
118	    state.flashMode = flashMode;
119	    state.flashOnMS = onMS;
120	    state.flashOffMS = offMS;
121	    state.brightnessMode = brightnessMode;
122	  
         //devices->lights是一个结构体，具体定义没找到，不过根据代码看，set_light应该是一个函数指针这里会根据不同的设备devices调用对应的set_light指向的具体函数
123	    devices->lights[light]->set_light(devices->lights[light], &state);
124	}

新代码截止


旧代码起始：

电源管理器(powermager)将brightness转给电源服务，该服务位置如下：

文件：frameworks/base/services/java/com/Android/server/PowerManagerService.java

public void setBacklightBrightness(int brightness) {
        mContext.enforceCallingOrSelfPermission(Android.Manifest.permission.DEVICE_POWER, null);

        // Don't let applications turn the screen all the way off
        brightness = Math.max(brightness, Power.BRIGHTNESS_DIM);

        mHardware.setLightBrightness_UNCHECKED(HardwareService.LIGHT_ID_BACKLIGHT, brightness, HardwareService.BRIGHTNESS_MODE_USER);
        mHardware.setLightBrightness_UNCHECKED(HardwareService.LIGHT_ID_KEYBOARD, (mKeyboardVisible ? brightness : 0), HardwareService.BRIGHTNESS_MODE_USER);
        mHardware.setLightBrightness_UNCHECKED(HardwareService.LIGHT_ID_BUTTONS, brightness, HardwareService.BRIGHTNESS_MODE_USER);
        long identity = Binder.clearCallingIdentity();
        try {
            mBatteryStats.noteScreenBrightness(brightness);
        } catch (RemoteException e) {
            Log.w(TAG, "RemoteException calling noteScreenBrightness on BatteryStatsService", e);
        } finally {
            Binder.restoreCallingIdentity(identity);
        }

        // update our animation state

        if (ANIMATE_SCREEN_LIGHTS) {
            mScreenBrightness.curValue = brightness;
            mScreenBrightness.animating = false;
            mScreenBrightness.targetValue = -1;
        }

        if (ANIMATE_KEYBOARD_LIGHTS) {
            mKeyboardBrightness.curValue = brightness;
            mKeyboardBrightness.animating = false;
              mKeyboardBrightness.targetValue = -1;
        }

        if (ANIMATE_BUTTON_LIGHTS) {

            mButtonBrightness.curValue = brightness;
            mButtonBrightness.animating = false;
            mButtonBrightness.targetValue = -1;
        }
    }

由以上代码可知， 同时设置了背光、键盘、按钮的亮度。 mHardware是硬件服务，通过该服务调用底层与设备打交道的C\C++代码， setLightBrightness_UNCHECKED原型如下：
文件：frameworks/base/services\java\com\Android\server\HardwareService.java

void setLightBrightness_UNCHECKED(int light, int brightness, int brightnessMode) {
                                                                               类型         亮度值                控制模式
        int b = brightness & 0x000000ff;
        b = 0xff000000 | (b << 16) | (b << 8) | b;
        setLight_native(mNativePointer, light, b, LIGHT_FLASH_NONE, 0, 0, brightnessMode);
     //  函数参见3.2
    }

参数说明：

int light 表示类型，选项如下：

    static final int LIGHT_ID_BACKLIGHT = 0; 

    static final int LIGHT_ID_KEYBOARD = 1;
    static final int LIGHT_ID_BUTTONS = 2;
    static final int LIGHT_ID_BATTERY = 3;
    static final int LIGHT_ID_NOTIFICATIONS = 4;
    static final int LIGHT_ID_ATTENTION = 5;
int brightness 表示亮度值
int brightnessMode 表示亮度的控制模式，选项如下： 
   static final int BRIGHTNESS_MODE_USER = 0;                  /** * Light brightness is managed by a user setting.      */
   static final int BRIGHTNESS_MODE_SENSOR = 1;             /*** Light brightness is managed by a light sensor.        */

由代码： 
        int b = brightness & 0x000000ff;
        b = 0xff000000 | (b << 16) | (b <<8 | b;
可知，亮度值在此进行了修改，即亮度值的格式变成：FFRRGGBB，FF是没有的，RR、GG、BB分别是256色的红绿蓝，并且红绿蓝的值都是一样的亮度值。

 

旧代码截止

 

3 硬件调用
3.1获取硬件
新代码：在文件：frameworks/base/services/jni/com_Android_server_LightService.cpp

旧代码：文件：frameworks/base/services/jni/com_Android_server_HardwareService.cpp

enum {
    LIGHT_INDEX_BACKLIGHT = 0,
    LIGHT_INDEX_KEYBOARD = 1,
    LIGHT_INDEX_BUTTONS = 2,
    LIGHT_INDEX_BATTERY = 3,
    LIGHT_INDEX_NOTIFICATIONS = 4,
    LIGHT_INDEX_ATTENTION = 5,
    LIGHT_COUNT
};

#define LIGHTS_HARDWARE_MODULE_ID "lights"

static jint init_native(JNIEnv *env, jobject clazz)
{
    int err;
    hw_module_t* module;
    Devices* devices;

    devices = (Devices*)malloc(sizeof(Devices));
    err = hw_get_module(LIGHTS_HARDWARE_MODULE_ID, (hw_module_t const**)&module);
    if (err == 0) {
        devices->lights[LIGHT_INDEX_BACKLIGHT]                   = get_device(module, LIGHT_ID_BACKLIGHT);
        devices->lights[LIGHT_INDEX_KEYBOARD]                    = get_device(module, LIGHT_ID_KEYBOARD);
        devices->lights[LIGHT_INDEX_BUTTONS]                       = get_device(module, LIGHT_ID_BUTTONS);
        devices->lights[LIGHT_INDEX_BATTERY]                        = get_device(module, LIGHT_ID_BATTERY);
        devices->lights[LIGHT_INDEX_NOTIFICATIONS]            = get_device(module, LIGHT_ID_NOTIFICATIONS);
        devices->lights[LIGHT_INDEX_ATTENTION]                    = get_device(module, LIGHT_ID_ATTENTION);
    } else {
          memset(devices, 0, sizeof(Devices));
    }
     return (jint)devices;
}

用 hw_get_module获取ID为LIGHTS_HARDWARE_MODULE_ID的硬件模块，该模块含有6个不同类型的亮度控制。
hw_get_module 的实现原理，如下：
文件：hardware/libhardware/Hardware.c

#define HAL_LIBRARY_PATH "/system/lib/hw"

static const char *variant_keys[ ] = {
    "ro.hardware",                /* This goes first so that it can pick up a different  file on the emulator. */
     "ro.product.board",
    "ro.board.platform",
    "ro.arch"
};

static const int HAL_VARIANT_KEYS_COUNT =    (sizeof(variant_keys)/sizeof(variant_keys[0]));

int hw_get_module(const char *id, const struct hw_module_t **module)
{   int status;
    int i;
    const struct hw_module_t *hmi = NULL;
    char prop[PATH_MAX];
    char path[PATH_MAX];
    /* Here we rely on the fact that calling dlopen multiple times on   the same .so will simply increment a refcount (and not load
     * a new copy of the library).   We also assume that dlopen() is thread-safe.
     */
      /* Loop through the configuration variants looking for a module */

    for (i=0 ; i<HAL_VARIANT_KEYS_COUNT+1 ; i++) {
        if (i < HAL_VARIANT_KEYS_COUNT) {
            if (property_get(variant_keys[i], prop, NULL) == 0) {
                continue;
            }

            snprintf(path, sizeof(path), "%s/%s.%s.so", HAL_LIBRARY_PATH, id, prop);
        }
       else {
            snprintf(path, sizeof(path), "%s/%s.default.so",  HAL_LIBRARY_PATH, id);
        }
        if (access(path, R_OK)) {
            continue;
        }
        /* we found a library matching this id/variant */
        break;
      }

    status = -ENOENT;
    if (i < HAL_VARIANT_KEYS_COUNT+1) {
        /* load the module, if this fails, we're doomed, and we should not try  to load a different variant. */
        status = load(id, path, module);
    }
     return status;
  }

property_get(variant_keys[i], prop, NULL) 会按如下顺序去获取如下变量所对应的值，然后返回给prop：
"ro.hardware",  

 "ro.product.board",
 "ro.board.platform",
 "ro.arch"

它们对应的变量为：
"ro.product.board=$TARGET_BOOTLOADER_BOARD_NAME"
"ro.board.platform=$TARGET_BOARD_PLATFORM"

如vendor/htc/dream-open/BoardConfig.mk里定义的TARGET_BOARD_PLATFORM := msm7k，则prop返回"msm7k ”，所以path= /system/lib/hw/lights. msm7k.so，也就是说要获取的硬件模块为lights. msm7k.so。

3.2调用硬件

setLight_native对应的jni C/C++代码是：
文件：frameworks/base/services/jni/com_Android_server_HardwareService.cpp

static void setLight_native(JNIEnv *env, jobject clazz, int ptr, int light, int colorARGB, int flashMode, int onMS, int offMS, int brightnessMode)
{
    Devices* devices = (Devices*)ptr;
    light_state_t state;
    if (light < 0 || light >= LIGHT_COUNT || devices->lights[light] == NULL) {
        return ;
    }
    memset(&state, 0, sizeof(light_state_t));
    state.color = colorARGB;
    state.flashMode = flashMode;
    state.flashOnMS = onMS;
    state.flashOffMS = offMS;
    state.brightnessMode = brightnessMode;
    devices->lights[light]->set_light(devices->lights[light], &state);
}

通过 light标识找到对应的light设备，然后再设置亮度。

3.3 硬件原型
msm7k的lights对应的硬件原型是在：hardware/msm7k/liblights
文件：hardware/msm7k/liblights/Android.mk

LOCAL_MODULE_PATH := $(TARGET_OUT_SHARED_LIBRARIES)/hw 
LOCAL_MODULE := lights.$(TARGET_BOARD_PLATFORM) 

也就是生成模块：/system/lib/hw/lights. msm7k.so

文件：hardware/msm7k/liblights/lights.c

/** Open a new instance of a lights device using name */
static int open_lights(const struct hw_module_t* module, char const* name,
        struct hw_device_t** device)
{
    int (*set_light)(struct light_device_t* dev,   struct light_state_t const* state);

    if (0 == strcmp(LIGHT_ID_BACKLIGHT, name)) {
        set_light = set_light_backlight;
       }

    else if (0 == strcmp(LIGHT_ID_KEYBOARD, name)) {
        set_light = set_light_keyboard;
    }
    else if (0 == strcmp(LIGHT_ID_BUTTONS, name)) {
        set_light = set_light_buttons;
    }
    else if (0 == strcmp(LIGHT_ID_BATTERY, name)) {
        set_light = set_light_battery;
    }
    else if (0 == strcmp(LIGHT_ID_NOTIFICATIONS, name)) {
        set_light = set_light_notifications;
    }
    else if (0 == strcmp(LIGHT_ID_ATTENTION, name)) {
        set_light = set_light_attention;
    }

    else {
        return -EINVAL;
    }

    pthread_once(&g_init, init_globals);
    struct light_device_t *dev = malloc(sizeof(struct light_device_t));
    memset(dev, 0, sizeof(*dev));
    dev->common.tag = HARDWARE_DEVICE_TAG;
    dev->common.version = 0;
    dev->common.module = (struct hw_module_t*)module;
    dev->common.close = (int (*)(struct hw_device_t*))close_lights;
    dev->set_light = set_light;
    *device = (struct hw_device_t*)dev;
    return 0;
}

static struct hw_module_methods_t lights_module_methods = {
    .open =  open_lights,
};

以上代码对应的是：

        devices->lights[LIGHT_INDEX_BACKLIGHT]     = get_device(module, LIGHT_ID_BACKLIGHT);
        devices->lights[LIGHT_INDEX_KEYBOARD]         = get_device(module, LIGHT_ID_KEYBOARD);
        devices->lights[LIGHT_INDEX_BUTTONS]             = get_device(module, LIGHT_ID_BUTTONS);
        devices->lights[LIGHT_INDEX_BATTERY]             = get_device(module, LIGHT_ID_BATTERY);
        devices->lights[LIGHT_INDEX_NOTIFICATIONS] = get_device(module, LIGHT_ID_NOTIFICATIONS);
        devices->lights[LIGHT_INDEX_ATTENTION]         = get_device(module, LIGHT_ID_ATTENTION);

也就是说，对不同的亮度设置给予了不同的设置函数。
举例，背光设置，背光对应的代码如下：

char const*const LCD_FILE         = "/sys/class/leds/lcd-backlight/brightness";

static int  rgb_to_brightness(struct light_state_t const* state) 
{ 
    int color = state->color & 0x00ffffff; 
    return ((77*((color>>16)&0x00ff))  + (150*((color>>8)&0x00ff)) + (29*(color&0x00ff))) >> 8;
} 

static int set_light_backlight(struct light_device_t* dev,      struct light_state_t const* state)
{ 
    int err = 0; 
    int brightness = rgb_to_brightness(state); 
    pthread_mutex_lock(&g_lock); 
    g_backlight = brightness; 
    err = write_int(LCD_FILE, brightness); 
    if (g_haveTrackballLight) { 
        handle_trackball_light_locked(dev); 
    } 

    pthread_mutex_unlock(&g_lock); 
    return err; 
} 

也就是 往文件/sys/class/leds/lcd-backlight/brightness写入亮度值，然后驱动会根据该文件更改背光的亮度。LCD_FILE的路径根据实际情况更改，同时需要在init.rc 修改其权限，使其可写rgb_to_brightness也根据实际更改，比如要直接亮度值控制，那只要获取r,g,b其中的一个值就行了，如：

static int rgb_to_brightness(struct light_state_t const* state) 
{ 
    int color = state->color & 0x000000ff; 
    return color; 
} 

4，led类驱动

4.1，驱动创建leds类，系统启动时执行leds_init在目录/sys/class/创建子目录leds
kernel\drivers\leds\Led-class.c

static int __init leds_init(void)
{
 leds_class = class_create(THIS_MODULE, "leds");
 if (IS_ERR(leds_class))
  return PTR_ERR(leds_class);
 leds_class->suspend = led_suspend;
 leds_class->resume = led_resume;
leds_class->dev_attrs = led_class_attrs;                                                //属性文件，sys下的接口，重点看一下
 return 0;
}

4.2，led_classdev_register，调用这个函数就在目录/sys/class/leds创建子目录led_cdev->name和属性文件brightness
对brightness文件写就执行led_brightness_store，对brightness文件读就执行led_brightness_show，为下面的lcd，led注册做好准备
因为：

kernel\drivers\leds\Led-class.c
C代码  

static ssize_t led_brightness_show(struct device *dev,
  struct device_attribute *attr, char *buf)
{
 struct led_classdev *led_cdev = dev_get_drvdata(dev);
 /* no lock needed for this */
 led_update_brightness(led_cdev);
 return sprintf(buf, "%u\n", led_cdev->brightness);
}

static ssize_t led_brightness_store(struct device *dev,
  struct device_attribute *attr, const char *buf, size_t size)
{
 struct led_classdev *led_cdev = dev_get_drvdata(dev);
 ssize_t ret = -EINVAL;
 char *after;
 unsigned long state = simple_strtoul(buf, &after, 10);
 size_t count = after - buf;

 if (*after && isspace(*after))
  count++;

 if (count == size) {
  ret = count;
  if (state == LED_OFF)
   led_trigger_remove(led_cdev);
  led_set_brightness(led_cdev, state);
 }
 return ret;
}

static inline void led_set_brightness(struct led_classdev *led_cdev,      enum led_brightness value) {  if (value > led_cdev->max_brightness)   value = led_cdev->max_brightness;  led_cdev->brightness = value;  if (!(led_cdev->flags & LED_SUSPENDED))   led_cdev->brightness_set(led_cdev, value); }

static struct device_attribute led_class_attrs[] = {  __ATTR(brightness, 0644, led_brightness_store, led_brightness_store),  __ATTR(max_brightness, 0644, led_max_brightness_show,led_max_brightness_store), #ifdef CONFIG_LEDS_TRIGGERS  __ATTR(trigger, 0644, led_trigger_show, led_trigger_store), #endif  __ATTR_NULL, }; /* led_classdev_register - register a new object of led_classdev class.
 * @parent: The device to register.
 * @led_cdev: the led_classdev structure for this device.
 */
int led_classdev_register(struct device *parent, struct led_classdev *led_cdev)
{
           int rc;
           led_cdev->dev = device_create(leds_class, parent, 0, led_cdev,    "%s", led_cdev->name);
           if (IS_ERR(led_cdev->dev))
          return PTR_ERR(led_cdev->dev);
 /* register the attributes */
          rc = device_create_file(led_cdev->dev, &dev_attr_brightness);
          if (rc)
                  goto err_out;

#ifdef CONFIG_LEDS_TRIGGERS
           init_rwsem(&led_cdev->trigger_lock);
#endif
 /* add to the list of leds */
           down_write(&leds_list_lock);
           list_add_tail(&led_cdev->node, &leds_list);
           up_write(&leds_list_lock);

            led_update_brightness(led_cdev);

#ifdef CONFIG_LEDS_TRIGGERS
          rc = device_create_file(led_cdev->dev, &dev_attr_trigger);
          if (rc)
                goto err_out_led_list;
          led_trigger_set_default(led_cdev);
#endif
          printk(KERN_INFO "Registered led device: %s\n",   led_cdev->name);
          return 0;

#ifdef CONFIG_LEDS_TRIGGERS
           err_out_led_list:
           device_remove_file(led_cdev->dev, &dev_attr_brightness);
           list_del(&led_cdev->node);
#endif
err_out:
            device_unregister(led_cdev->dev);
            return rc;
}
EXPORT_SYMBOL_GPL(led_classdev_register);

4.3，lcd驱动 调用led_classdev_register，在目录/sys/class/leds创建子目录lcd- backlight和属性文件brightness

kernel\drivers\video\msm\Msm_fb.c

static int lcd_backlight_registered;
static void msm_fb_set_bl_brightness(struct led_classdev *led_cdev, enum led_brightness value)
{
 struct msm_fb_data_type *mfd = dev_get_drvdata(led_cdev->dev->parent);
 int bl_lvl;

 if (value > MAX_BACKLIGHT_BRIGHTNESS)
  value = MAX_BACKLIGHT_BRIGHTNESS;

 /* This maps Android backlight level 0 to 255 into
    driver backlight level 0 to bl_max with rounding */
 bl_lvl = (2 * value * mfd->panel_info.bl_max + MAX_BACKLIGHT_BRIGHTNESS)  /(2 * MAX_BACKLIGHT_BRIGHTNESS);

 if (!bl_lvl && value)     bl_lvl = 1;
 msm_fb_set_backlight(mfd, bl_lvl, 1);
}

static struct led_classdev backlight_led = {
 .name  = "lcd-backlight",
 .brightness = MAX_BACKLIGHT_BRIGHTNESS,
 .brightness_set = msm_fb_set_bl_brightness,
};

 if (!lcd_backlight_registered) {
  if (led_classdev_register(&pdev->dev, &backlight_led))
   printk(KERN_ERR "led_classdev_register failed\n");
  else
   lcd_backlight_registered = 1;
 }

就在目录/sys/class/leds创建子目录 lcd-backlight和属性文件brightness
当按键或者来的或者改变lcd亮度时，上层对属性文件/sys/class/leds/lcd-backlight/brightness写入背光的亮度数值就
调用led_brightness_store >>调用simple_strtoul(buf, &after, 10);将输入的字符串转换为10进制的数字
然后接着执行led_set_brightness ，内部会调用执行led_cdev->brightness_set(led_cdev, value)，也就是调用》msm_fb_set_bl_brightness ，

因为  .brightness_set = msm_fb_set_bl_brightness,

msm_fb_set_bl_brightness函数里面代码：
/* This maps Android backlight level 0 to 255 into    driver backlight level 0 to bl_max with rounding */
bl_lvl = (2 * value * mfd->panel_info.bl_max + MAX_BACKLIGHT_BRIGHTNESS)  /(2 * MAX_BACKLIGHT_BRIGHTNESS);
将输入的0--255转换为IC的0--bl_max

msm_fb_set_bl_brightness 里面同时还调用 msm_fb_set_backlight(mfd, bl_lvl, 1);

其代码如下：

void msm_fb_set_backlight(struct msm_fb_data_type *mfd, __u32 bkl_lvl)
{ struct msm_fb_panel_data *pdata;
  if (!mfd->panel_power_on || !bl_updated) {
  unset_bl_level = bkl_lvl;
  return;
  } else {
       unset_bl_level = 0;
  }
  pdata = (struct msm_fb_panel_data *)mfd->pdev->dev.platform_data;

  if ((pdata) && (pdata->set_backlight)) {
      down(&mfd->sem);
      if (bl_level_old == bkl_lvl) {
      up(&mfd->sem);
      return;
  }

    mfd->bl_level = bkl_lvl;     // mdf->bl_level在具体的lcd驱动文件中的xxx_set_backlight()函数中会调用
    pdata->set_backlight(mfd);   //调用xxx_set_backlight()函数
    bl_level_old = mfd->bl_level;
    up(&mfd->sem);        
    }
}

最终改变LCD的背光驱动电路的设置，调节LCD的背光的亮度

4.4 键盘背光灯

上层对属性文件/sys/class/leds/keyboard-backlight/brightness写入背光的亮度数值
(kernel\drivers\leds\Leds-msm-pmic.c

#define MAX_KEYPAD_BL_LEVEL 16

static void msm_keypad_bl_led_set(struct led_classdev *led_cdev,
 enum led_brightness value)
{
            int ret;
            ret = pmic_set_led_intensity(LED_KEYPAD, value / MAX_KEYPAD_BL_LEVEL);
           if (ret)
            dev_err(led_cdev->dev, "can't set keypad backlight\n");
}

static struct led_classdev msm_kp_bl_led = {
      .name   = "keyboard-backlight",
      .brightness_set  = msm_keypad_bl_led_set,
      .brightness  = LED_OFF,
};

static int msm_pmic_led_probe(struct platform_device *pdev)
{
           int rc;

           rc = led_classdev_register(&pdev->dev, &msm_kp_bl_led);
           if (rc) {
                    dev_err(&pdev->dev, "unable to register led class driver\n");
                    return rc;
           }
          msm_keypad_bl_led_set(&msm_kp_bl_led, LED_OFF);
          return rc;
}

static int __devexit msm_pmic_led_remove(struct platform_device *pdev)
{
     led_classdev_unregister(&msm_kp_bl_led);
     return 0;
}

#ifdef CONFIG_PM
static int msm_pmic_led_suspend(struct platform_device *dev,     pm_message_t state)
{
    led_classdev_suspend(&msm_kp_bl_led);
    return 0;
}

static int msm_pmic_led_resume(struct platform_device *dev)
{
        led_classdev_resume(&msm_kp_bl_led);
         return 0;
}
#else
#define msm_pmic_led_suspend NULL
#define msm_pmic_led_resume NULL
#endif

static struct platform_driver msm_pmic_led_driver = {
 .probe  = msm_pmic_led_probe,
 .remove  = __devexit_p(msm_pmic_led_remove),
 .suspend = msm_pmic_led_suspend,
 .resume  = msm_pmic_led_resume,
 .driver  = {
  .name = "pmic-leds",
  .owner = THIS_MODULE,
 },
};

static int __init msm_pmic_led_init(void)
{
          return platform_driver_register(&msm_pmic_led_driver);
}
module_init(msm_pmic_led_init);

static void __exit msm_pmic_led_exit(void)
{
          platform_driver_unregister(&msm_pmic_led_driver);
}
module_exit(msm_pmic_led_exit);

MODULE_DESCRIPTION("MSM PMIC LEDs driver");
MODULE_LICENSE("GPL v2");
MODULE_ALIAS("platform:p

系统行动执行msm_pmic_led_init(void) ，实质是调用》 platform_driver_register(&msm_pmic_led_driver);
接着调用msm_pmic_led_probe ，完成调用 led_classdev_register(&pdev->dev, &msm_kp_bl_led);

就在目录/sys/class/leds创建子目录 keyboard-backlight和属性文件brightness
当按键时，上层对属性文件/sys/class/leds/keyboard-backlight/brightness写入背光的亮度数值就
调用led_brightness_store ，从而调用simple_strtoul(buf, &after, 10);将输入的字符串转换为10进制的数字
然后执行led_set_brightness，》》》》执行led_cdev->brightness_set(led_cdev, value
调用msm_keypad_bl_led_set ，因为 .brightness_set  =msm_keypad_bl_led_set,
调用 ret = pmic_set_led_intensity(LED_KEYPAD, value / MAX_KEYPAD_BL_LEVEL);
最终改变LED驱动电路的设置，调节LED的亮度

 

参考另外另外两文章总结：