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：

[html] view plain copy/sys/class/backlight/pwm-backlight/brightness

只要

[html] view plain copyecho 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：

[html] view plain copyFrameworks/base/services/jni/com_android_server_LightsService.cpp

Frameworks/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。

[html] view plain copy#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,
};

对于这个代码，主要是修改下

[html] view plain copychar 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

[html] view plain copychar const *const LCD_FILE = "/sys/class/backlight/pwm-backlight/brightness";

至于

[html] view plain copychar 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。

[html] view plain copychown 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。