和菜鳥一起學android4.0.3源碼之lcd螢幕背光調節

          周六的中午還是依舊來了公司，本來也沒有打算來的，既然來了，那就把上次遺留下來的一些問題給解決吧，把android下的pwm調lcd背光給總結下吧。關於android的背光，是用pwm波來控制的，通過占空比的不同，得到不同的電壓值，從而點亮的lcd的亮度就不同了。具體的也就是控制了電壓值而已。

           要在android上層搞定背光的調節，那麼必須準備底層驅動了，首先就是那個backlight了，這個linux驅動的模型已經做好了，只要選上就ok了。

      Device下的graphics support

 

選上那個backlight就好了

 

        還有要準備相應平台的pwm的驅動，準備好這些後，就ok了。然後跑一下就會產生一個節點：

/sys/class/backlight/pwm-backlight/brightness

只要

echo 100 >  /sys/class/backlight/pwm-backlight/brightness    echo 50 >  /sys/class/backlight/pwm-backlight/brightness

        如果背光改變了，那麼就說明驅動OK了，也可以用示波器看pwm引腳，是否有變換。

        如果不成功，那麼就繼續調試底層驅動吧。接著就是要上android了。

      
對於背光，android代碼中主要是：

Frameworks/base/services/jni/com_android_server_LightsService.cppFrameworks/base/services/java/com/android/server/LightsServer.java

        這裡就不用太去關注了，移植到android主要就是硬體抽象層的事情了，java層會調用jni層，jni層會調到相應的硬體抽象層，硬體抽象層再繼續調用底層驅動。好了，還是看看lcd背光的硬體抽象層吧。

對於不同平台那個lights.c是放在不同地方的，比如你的是samsung的tuna平台，那麼就  

        在/device/Samsung/tuna/liblights/lights.c下。

#define LOG_TAG "lights"#include <cutils/log.h>#include <stdint.h>#include <string.h>#include <errno.h>#include <fcntl.h>#include <pthread.h>#include <sys/ioctl.h>#include <sys/types.h>#include <hardware/lights.h>#include <linux/leds-an30259a.h> static pthread_once_t g_init = PTHREAD_ONCE_INIT;static pthread_mutex_t g_lock = PTHREAD_MUTEX_INITIALIZER; char const *const LCD_FILE = "/sys/class/backlight/s6e8aa0/brightness";char const *const LED_FILE = "/dev/an30259a_leds"; #define IMAX 0 // 12.75mA power consumption // Slope values, based on total blink of 1000ms#define SLOPE_UP_1          450#define SLOPE_UP_2          (500-SLOPE_UP_1)#define SLOPE_DOWN_1    SLOPE_UP_2#define SLOPE_DOWN_2    SLOPE_UP_1// brightness at mid-slope, on 0 - 127 scale#define MID_BRIGHTNESS  31 void init_g_lock(void){       pthread_mutex_init(&g_lock, NULL);} static int write_int(char const *path, int value){       int fd;       static int already_warned;        already_warned = 0;        LOGV("write_int: path %s, value %d", path, value);       fd = open(path, O_RDWR);        if (fd >= 0) {              char buffer[20];              int bytes = sprintf(buffer, "%d\n", value);              int amt = write(fd, buffer, bytes);              close(fd);              return amt == -1 ? -errno : 0;       } else {              if (already_warned == 0) {                     LOGE("write_int failed to open %s\n", path);                     already_warned = 1;              }              return -errno;       }} 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);       err = write_int(LCD_FILE, brightness);        pthread_mutex_unlock(&g_lock);       return err;} static int close_lights(struct light_device_t *dev){       LOGV("close_light is called");       if (dev)              free(dev);        return 0;} /* LEDs */static int write_leds(struct an30259a_pr_control *led){       int err = 0;       int imax = IMAX;       int fd;        pthread_mutex_lock(&g_lock);        fd = open(LED_FILE, O_RDWR);       if (fd >= 0) {              err = ioctl(fd, AN30259A_PR_SET_IMAX, &imax);              if (err)                     LOGE("failed to set imax");               err = ioctl(fd, AN30259A_PR_SET_LED, led);              if (err < 0)                     LOGE("failed to set leds!");               close(fd);       } else {              LOGE("failed to open %s!", LED_FILE);              err =  -errno;       }        pthread_mutex_unlock(&g_lock);        return err;} static int set_light_leds(struct light_state_t const *state, int type){       struct an30259a_pr_control led;        memset(&led, 0, sizeof(led));        switch (state->flashMode) {       case LIGHT_FLASH_NONE:              led.state = LED_LIGHT_OFF;              break;       case LIGHT_FLASH_TIMED:       case LIGHT_FLASH_HARDWARE:              led.state = LED_LIGHT_SLOPE;              led.color = state->color & 0x00ffffff;              // tweak to eliminate purplish tint from white color              if (led.color == 0x00ffffff)                  led.color = 0x80ff80;              // scale slope times based on flashOnMS              led.time_slope_up_1 = (SLOPE_UP_1 * state->flashOnMS) / 1000;              led.time_slope_up_2 = (SLOPE_UP_2 * state->flashOnMS) / 1000;              led.time_slope_down_1 = (SLOPE_DOWN_1 * state->flashOnMS) / 1000;              led.time_slope_down_2 = (SLOPE_DOWN_2 * state->flashOnMS) / 1000;              led.mid_brightness = MID_BRIGHTNESS;              led.time_off = state->flashOffMS;              break;       default:              return -EINVAL;       }        return write_leds(&led);} static int set_light_leds_notifications(struct light_device_t *dev,                     struct light_state_t const *state){       return set_light_leds(state, 0);} static int set_light_leds_attention(struct light_device_t *dev,                     struct light_state_t const *state){       return set_light_leds(state, 1);} 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_NOTIFICATIONS, name))              set_light = set_light_leds_notifications;       else if (0 == strcmp(LIGHT_ID_ATTENTION, name))              set_light = set_light_leds_attention;       else              return -EINVAL;        pthread_once(&g_init, init_g_lock);        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,}; const struct hw_module_t HAL_MODULE_INFO_SYM = {       .tag = HARDWARE_MODULE_TAG,       .version_major = 1,       .version_minor = 0,       .id = LIGHTS_HARDWARE_MODULE_ID,       .name = "lights Module",       .author = "Google, Inc.",       .methods = &lights_module_methods,};

 

        對於這個代碼，主要是修改下

char const *const LCD_FILE = "/sys/class/backlight/s6e8aa0/brightness";

        背光其實就是開啟這個節點，往裡面寫資料而已，所以，要把這個節點改為自己的平台的節點就可以了。

這裡我們改為

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

 

        至於

char const *const LED_FILE = "/dev/an30259a_leds";

         這個，應該就是提示燈的節點吧，不管他。然後再mm下，得到了一個lights.default.so，然後替換掉這個.so就好了。

         還有就是許可權問題了，開啟這個節點是要許可權的，那麼我們可以在init.xxx.rc中加上許可權就好了。

chown system system /sys/class/backlight/pwm-backlight/brightness

 

        OK，這樣，那麼android那個調節螢幕亮度的UI介面就可以控制lcd的背光了。