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
Java代码
1. private static final int MINIMUM_BACKLIGHT = Android.os.Power.BRIGHTNESS_DIM + 10;
2. private static final int MAXIMUM_BACKLIGHT = Android.os.Power.BRIGHTNESS_ON;
3. 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
1. public void onCheckedChanged(CompoundButton buttonView, boolean
2. setMode(isChecked ? Settings.System.SCREEN_BRIGHTNESS_MODE_AUTOMATIC
3. : Settings.System.SCREEN_BRIGHTNESS_MODE_MANUAL);
4. if
5. setBrightness(mSeekBar.getProgress() + MINIMUM_BACKLIGHT);
6. }
7. }
8.
9. private void setBrightness(int
10. try
11. IPowerManager power = IPowerManager.Stub.asInterface(
12. "power"));
13. if (power != null) {
14. power.setBacklightBrightness(brightness);
15. }
16. catch
17. }
18. }
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
1. /** * sets the brightness of the backlights (screen, keyboard, button).
2. *
3. * @param brightness value from 0 to 255
4. *
5. * {@hide}
6. */
7.
8. public void setBacklightBrightness(int
9. {
10. try
11. setBacklightBrightness(brightness);
12. catch
13. }
14. }
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
Java代码
1. public void setBacklightBrightness(int
2. null);
3.
4. // Don't let applications turn the screen all the way off
5. brightness = Math.max(brightness, Power.BRIGHTNESS_DIM);
6.
7. mHardware.setLightBrightness_UNCHECKED(HardwareService.LIGHT_ID_BACKLIGHT, brightness, HardwareService.BRIGHTNESS_MODE_USER);
8. mHardware.setLightBrightness_UNCHECKED(HardwareService.LIGHT_ID_KEYBOARD, (mKeyboardVisible ? brightness : 0), HardwareService.BRIGHTNESS_MODE_USER);
9. mHardware.setLightBrightness_UNCHECKED(HardwareService.LIGHT_ID_BUTTONS, brightness, HardwareService.BRIGHTNESS_MODE_USER);
10. long
11. try
12. mBatteryStats.noteScreenBrightness(brightness);
13. catch
14. "RemoteException calling noteScreenBrightness on BatteryStatsService", e);
15. finally
16. Binder.restoreCallingIdentity(identity);
17. }
18.
19. // update our animation state
20.
21. if
22. mScreenBrightness.curValue = brightness;
23. false;
24. 1;
25. }
26.
27. if
28. mKeyboardBrightness.curValue = brightness;
29. false;
30. 1;
31. }
32.
33. if
34.
35. mButtonBrightness.curValue = brightness;
36. false;
37. 1;
38. }
39. } 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
Java代码
1. void setLightBrightness_UNCHECKED(int light, int brightness, int brightnessMode) {
2. 类型 亮度值 控制模式
3. int b = brightness & 0x000000ff;
4. 0xff000000 | (b << 16) | (b << 8) | b;
5. setLight_native(mNativePointer, light, b, LIGHT_FLASH_NONE, 0, 0, brightnessMode);
6. // 函数参见3.2
7. }
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
Cpp代码
1. enum
2. LIGHT_INDEX_BACKLIGHT = 0,
3. LIGHT_INDEX_KEYBOARD = 1,
4. LIGHT_INDEX_BUTTONS = 2,
5. LIGHT_INDEX_BATTERY = 3,
6. LIGHT_INDEX_NOTIFICATIONS = 4,
7. LIGHT_INDEX_ATTENTION = 5,
8. LIGHT_COUNT
9. };
10.
11. #define LIGHTS_HARDWARE_MODULE_ID "lights"
12.
13. static
14. {
15. int
16. hw_module_t* module;
17. Devices* devices;
18.
19. sizeof(Devices));
20. err = hw_get_module(LIGHTS_HARDWARE_MODULE_ID, (hw_module_t const**)&module);
21. if
22. devices->lights[LIGHT_INDEX_BACKLIGHT] = get_device(module, LIGHT_ID_BACKLIGHT);
23. devices->lights[LIGHT_INDEX_KEYBOARD] = get_device(module, LIGHT_ID_KEYBOARD);
24. devices->lights[LIGHT_INDEX_BUTTONS] = get_device(module, LIGHT_ID_BUTTONS);
25. devices->lights[LIGHT_INDEX_BATTERY] = get_device(module, LIGHT_ID_BATTERY);
26. devices->lights[LIGHT_INDEX_NOTIFICATIONS] = get_device(module, LIGHT_ID_NOTIFICATIONS);
27. devices->lights[LIGHT_INDEX_ATTENTION] = get_device(module, LIGHT_ID_ATTENTION);
28. else
29. sizeof(Devices));
30. }
31. return
32. } 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
C代码
1. #define HAL_LIBRARY_PATH "/system/lib/hw"
2.
3. static const char *variant_keys[ ] = {
4. "ro.hardware", /* This goes first so that it can pick up a different file on the emulator. */
5. "ro.product.board",
6. "ro.board.platform",
7. "ro.arch"
8. };
9.
10. static const int HAL_VARIANT_KEYS_COUNT = (sizeof(variant_keys)/sizeof(variant_keys[0]));
11.
12. int hw_get_module(const char *id, const struct
13. { int
14. int
15. const struct
16. char
17. char
18. /* Here we rely on the fact that calling dlopen multiple times on the same .so will simply increment a refcount (and not load
19. * a new copy of the library). We also assume that dlopen() is thread-safe.
20. */
21. /* Loop through the configuration variants looking for a module */
22.
23. for
24. if
25. if (property_get(variant_keys[i], prop, NULL) == 0) {
26. continue;
27. }
28.
29. path, sizeof(path), "%s/%s.%", HAL_LIBRARY_PATH, id, prop);
30. }
31. else
32. sizeof(path), "%s/%", HAL_LIBRARY_PATH, id);
33. }
34. if
35. continue;
36. }
37. /* we found a library matching this id/variant */
38. break;
39. }
40.
41. status = -ENOENT;
42. if
43. /* load the module, if this fails, we're doomed, and we should not tryto load a different variant. */
44. status = load(id, path, module);
45. }
46. return
47. }
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/里定义的TARGET_BOARD_PLATFORM := msm7k，则prop返回"msm7k ”，所以path= /system/lib/hw/lights. ，也就是说要获取的硬件模块为lights. 。
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
Cpp代码
1. static void setLight_native(JNIEnv *env, jobject clazz, int ptr, int light, int colorARGB, int flashMode, int onMS, int offMS, int brightnessMode)
2. {
3. Devices* devices = (Devices*)ptr;
4. light_state_t state;
5. if (light < 0 || light >= LIGHT_COUNT || devices->lights[light]
6. return
7. }
8. sizeof(light_state_t));
9. state.color = colorARGB;
10. state.flashMode = flashMode;
11. state.flashOnMS = onMS;
12. state.flashOffMS = offMS;
13. state.brightnessMode = brightnessMode;
14. devices->lights[light]->set_light(devices->lights[light], &state);
15. } 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.
文件：hardware/msm7k/liblights/lights.c
C代码
1. /** Open a new instance of a lights device using name */
2. static int open_lights(const struct hw_module_t* module, char const* name,
3. struct
4. {
5. int (*set_light)(struct light_device_t* dev, struct light_state_t const* state);
6.
7. if (0 == strcmp(LIGHT_ID_BACKLIGHT, name)) {
8. set_light = set_light_backlight;
9. }
10.
11. else if (0 == strcmp(LIGHT_ID_KEYBOARD, name)) {
12. set_light = set_light_keyboard;
13. }
14. else if
15. set_light = set_light_buttons;
16. }
17. else if
18. set_light = set_light_battery;
19. }
20. else if
21. set_light = set_light_notifications;
22. }
23. else if
24. set_light = set_light_attention;
25. }
26.
27. else
28. return
29. }
30.
31. pthread_once(&g_init, init_globals);
32. struct light_device_t *dev = malloc(sizeof(struct
33. sizeof(*dev));
34. dev->common.tag = HARDWARE_DEVICE_TAG;
35. dev->common.version = 0;
36. struct
37. int (*)(struct
38. set_light;
39. struct
40. return
41. }
42.
43. static struct
44. .open = open_lights,
45. }; 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
C代码
1. static int __init leds_init(void)
2. {
3. leds_class = class_create(THIS_MODULE, "leds");
4. if
5. return
6. leds_class->suspend = led_suspend;
7. leds_class->resume = led_resume;
8. leds_class->dev_attrs = led_class_attrs; //属性文件，sys下的接口，重点看一下
9. return
10. }
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
1. static ssize_t led_brightness_show(struct
2. struct device_attribute *attr, char
3. {
4. struct
5. /* no lock needed for this */
6. led_update_brightness(led_cdev);
7. return sprintf(buf, "%u\n", led_cdev->brightness);
8. }
9.
10. static ssize_t led_brightness_store(struct
11. struct device_attribute *attr, const char *buf, size_t
12. {
13. struct
14. ssize_t ret = -EINVAL;
15. char
16. long state = simple_strtoul(buf, &after, 10);
17. size_t
18.
19. if
20. count++;
21.
22. if
23. ret = count;
24. if
25. led_trigger_remove(led_cdev);
26. led_set_brightness(led_cdev, state);
27. }
28. return
29. }
30.
31. 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);
}32.
33. 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.34. * @parent: The device to register.
35. * @led_cdev: the led_classdev structure for this device.
36. */
37. int led_classdev_register(struct device *parent, struct
38. {
39. int
40. "%s", led_cdev->name);
41. if
42. return
43. /* register the attributes */
44. rc = device_create_file(led_cdev->dev, &dev_attr_brightness);
45. if
46. goto
47.
48. #ifdef CONFIG_LEDS_TRIGGERS
49. init_rwsem(&led_cdev->trigger_lock);
50. #endif
51. /* add to the list of leds */
52. down_write(&leds_list_lock);
53. list_add_tail(&led_cdev->node, &leds_list);
54. up_write(&leds_list_lock);
55.
56. led_update_brightness(led_cdev);
57.
58. #ifdef CONFIG_LEDS_TRIGGERS
59. rc = device_create_file(led_cdev->dev, &dev_attr_trigger);
60. if
61. goto
62. led_trigger_set_default(led_cdev);
63. #endif
64. "Registered led device: %s\n", led_cdev->name);
65. return
66.
67. #ifdef CONFIG_LEDS_TRIGGERS
68. err_out_led_list:
69. device_remove_file(led_cdev->dev, &dev_attr_brightness);
70. list_del(&led_cdev->node);
71. #endif
72. err_out:
73. device_unregister(led_cdev->dev);
74. return
75. }
76. 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
C代码
1. static int
2. static void msm_fb_set_bl_brightness(struct led_classdev *led_cdev, enum led_brightness value)
3. {
4. struct
5. int
6.
7. if
8. value = MAX_BACKLIGHT_BRIGHTNESS;
9.
10. /* This maps Android backlight level 0 to 255 into
11. driver backlight level 0 to bl_max with rounding */
12. bl_lvl
13.
14. if
15. msm_fb_set_backlight(mfd, bl_lvl, 1);
16. }
17.
18. static struct
19. "lcd-backlight",
20. .brightness = MAX_BACKLIGHT_BRIGHTNESS,
21. .brightness_set = msm_fb_set_bl_brightness,
22. };
23.
24. if
25. if (led_classdev_register(&pdev->dev, &backlight_led))
26. "led_classdev_register failed\n");
27. else
28. lcd_backlight_registered = 1;
29. }
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
C代码
1. #define MAX_KEYPAD_BL_LEVEL 16
2.
3. static void msm_keypad_bl_led_set(struct
4. enum
5. {
6. int
7. ret = pmic_set_led_intensity(LED_KEYPAD, value / MAX_KEYPAD_BL_LEVEL);
8. if
9. "can't set keypad backlight\n");
10. }
11.
12. static struct
13. "keyboard-backlight",
14. msm_keypad_bl_led_set,
15. .brightness = LED_OFF,
16. };
17.
18. static int msm_pmic_led_probe(struct
19. {
20. int
21.
22. rc = led_classdev_register(&pdev->dev, &msm_kp_bl_led);
23. if
24. "unable to register led class driver\n");
25. return
26. }
27. msm_keypad_bl_led_set(&msm_kp_bl_led, LED_OFF);
28. return
29. }
30.
31. static int __devexit msm_pmic_led_remove(struct
32. {
33. led_classdev_unregister(&msm_kp_bl_led);
34. return
35. }
36.
37. #ifdef CONFIG_PM
38. static int msm_pmic_led_suspend(struct
39. {
40. led_classdev_suspend(&msm_kp_bl_led);
41. return
42. }
43.
44. static int msm_pmic_led_resume(struct
45. {
46. led_classdev_resume(&msm_kp_bl_led);
47. return
48. }
49. #else
50. #define msm_pmic_led_suspend NULL
51. #define msm_pmic_led_resume NULL
52. #endif
53.
54. static struct platform_driver msm_pmic_led_driver = {
55. msm_pmic_led_probe,
56. .remove = __devexit_p(msm_pmic_led_remove),
57. .suspend = msm_pmic_led_suspend,
58. .resume = msm_pmic_led_resume,
59. .driver = {
60. "pmic-leds",
61. .owner = THIS_MODULE,
62. },
63. };
64.
65. static int __init msm_pmic_led_init(void)
66. {
67. return platform_driver_register(&msm_pmic_led_driver);
68. }
69. module_init(msm_pmic_led_init);
70.
71. static void __exit msm_pmic_led_exit(void)
72. {
73. platform_driver_unregister(&msm_pmic_led_driver);
74. }
75. 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
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