和菜鸟一起学android4.0.3源码之lcd屏幕背光调节

周六的中午还是依旧来了公司，本来也没有打算来的，既然来了，那就把上次遗留下来的一些问题给解决吧，把android下的pwm调lcd背光给总结下吧。关于android的背光，是用pwm波来控制的，通过占空比的不同，得到不同的电压值，从而点亮的lcd的亮度就不同了。具体的也就是控制了电压值而已。

要在android上层搞定背光的调节，那么必须准备底层驱动了，首先就是那个backlight了，这个linux驱动的模型已经做好了，只要选上就ok了。

Device下的graphics support

选上那个backlight就好了

还有要准备相应平台的pwm的驱动，准备好这些后，就ok了。然后跑一下就会生成一个节点：

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

只要

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

如果背光改变了，那么就说明驱动OK了，也可以用示波器看pwm引脚，是否有变换。

如果不成功，那么就继续调试底层驱动吧。接着就是要上android了。

对于背光，android代码中主要是：

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

这里就不用太去关注了，移植到android主要就是硬件抽象层的事情了，java层会调用jni层，jni层会调到相应的硬件抽象层，硬件抽象层再继续调用底层驱动。好了，还是看看lcd背光的硬件抽象层吧。

对于不同平台那个lights.c是放在不同地方的，比如你的是samsung的tuna平台，那么就

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  31void 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,};

对于这个代码，主要是修改下

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

背光其实就是打开这个节点，往里面写数据而已，所以，要把这个节点改为自己的平台的节点就可以了。

这里我们改为

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

至于

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

这个，应该就是提示灯的节点吧，不管他。然后再mm下，得到了一个lights.default.so，然后替换掉这个.so就好了。

还有就是权限问题了，打开这个节点是要权限的，那么我们可以在init.xxx.rc中加上权限就好了。

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

OK，这样，那么android那个调节屏幕亮度的UI界面就可以控制lcd的背光了。

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