Android(安卓)LCD和键盘背光亮度设置

原地址： 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

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

/**     * 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) {        }}

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) {        int b = brightness & 0x000000ff;        b = 0xff000000 | (b << 16) | (b << 8) | b;        setLight_native(mNativePointer, light, b, LIGHT_FLASH_NONE, 0, 0, brightnessMode);    }

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：

/**

* Light brightness is managed by a user setting.

*/

static final int BRIGHTNESS_MODE_USER = 0;

/**

* Light brightness is managed by a light sensor.

*/

static final int BRIGHTNESS_MODE_SENSOR = 1;

由代码：

int b = brightness & 0x000000ff;

b = 0xff000000 | (b << 16) | (b << | 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。

3 硬件调用
3.1获取硬件
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", /* This goes first so that it can pick up a different

file on the emulator. */

"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; 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

kernel\drivers\leds\Led-class.c

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 DEVICE_ATTR(brightness, 0644, led_brightness_show, led_brightness_store);/** * 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_TRIGGERSerr_out_led_list: device_remove_file(led_cdev->dev, &dev_attr_brightness); list_del(&led_cdev->node);#endiferr_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
执行led_set_brightness

执行led_cdev->brightness_set(led_cdev, value

调用msm_fb_set_bl_brightness ，因为 .brightness_set = msm_fb_set_bl_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);
将输入的0--255转换为IC的0--bl_max

调用 msm_fb_set_backlight(mfd, bl_lvl, 1);

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 16static 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_PMstatic 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#endifstatic 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)
调用 platform_driver_register(&msm_pmic_led_driver);

调用msm_pmic_led_probe

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

调用simple_strtoul(buf, &after, 10);将输入的字符串转换为10进制的数字

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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