Android模拟器学framework和driver之battery & backlight-----6. backlight in hal

这里我们来介绍下backlight hal层，和之前一样，跟之前我们介绍的temperature的hal差不多，比sensor的hal还简单，这里我就不多说hal的介绍了，之前都有介绍的比较详细了，不清楚的可以参考前面的文章：

http://blog.csdn.net/zhangjie201412/article/details/7225617

首先要明确我们的目标，这里主要是封装一些方法，然后给android framework层使用（jni layer），打开一个sysfs中的节点，然后read/write，

明白这点就够了，直接贴代码：

/hardware/libhardware/module/lights/android_light.c

[cpp]
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#define LOG_TAG "light"

#include <hardware/lights.h>

#include <fcntl.h>
#include <errno.h>

#include <stdlib.h>
#include <cutils/log.h>

#include <cutils/atomic.h>
#include <cutils/properties.h>

#define MAX_BRIGHTNESS 255

#define DEF_BACKLIGHT_DEV "android-backlight"

#define DEF_BACKLIGHT_PATH "/sys/class/backlight/"

/***************************************************************/
struct lights_module_t{
struct hw_module_t common;
};

static int lights_device_open(const struct hw_module_t* module,
const char* name,struct hw_device_t** device);

static struct hw_module_methods_t lights_module_methods = {
.open=lights_device_open
};

const struct lights_module_t HAL_MODULE_INFO_SYM = {
.common= {
.tag= HARDWARE_MODULE_TAG,
.version_major= 1,
.version_minor= 0,
.id= LIGHTS_HARDWARE_MODULE_ID,
.name= "Lights module",
.author= "Freescale Semiconductor",
.methods= &lights_module_methods,
}
};

static char max_path[256], path[256];
// ****************************************************************************

// module
// ****************************************************************************

static int set_light_backlight(struct light_device_t* dev,
struct light_state_t const* state)
{
int result = -1;
unsigned int color = state->color;
unsigned int brightness = 0, max_brightness = 0;
FILE *file;

brightness = ((77*((color>>16)&0x00ff)) + (150*((color>>8)&0x00ff)) +
(29*(color&0x00ff))) >> 8;
LOGV("set_light, get brightness=%d", brightness);

file = fopen(max_path, "r");
if (!file) {
LOGE("can not open file %s\n", max_path);
return result;
}
fread(&max_brightness, 1, 3, file);
fclose(file);

max_brightness = atoi((char *) &max_brightness);
brightness = brightness * max_brightness / MAX_BRIGHTNESS;
LOGV("set_light, max_brightness=%d, target brightness=%d",
max_brightness, brightness);

file = fopen(path, "w");
if (!file) {
LOGE("can not open file %s\n", path);
return result;
}
fprintf(file, "%d", brightness);
fclose(file);

result = 0;
return result;
}

static int light_close_backlight(struct hw_device_t *dev)
{
struct light_device_t *device = (struct light_device_t*)dev;
if (device)
free(device);
return 0;
}

/*****************************************************************************/
static int lights_device_open(const struct hw_module_t* module,
const char* name, struct hw_device_t** device)
{
int status = -EINVAL;
LOGV("lights_device_open\n");
if (!strcmp(name, LIGHT_ID_BACKLIGHT)) {
struct light_device_t *dev;
char value[PROPERTY_VALUE_MAX];

dev = malloc(sizeof(*dev));

/* initialize our state here */
memset(dev, 0, sizeof(*dev));

/* initialize the procs */
dev->common.tag = HARDWARE_DEVICE_TAG;
dev->common.version = 0;
dev->common.module = (struct hw_module_t*) module;
dev->common.close = light_close_backlight;

dev->set_light = set_light_backlight;

*device = &dev->common;

// property_get("hw.backlight.dev", value, DEF_BACKLIGHT_DEV);

// strcpy(path, DEF_BACKLIGHT_PATH);

// strcat(path, value);

// strcpy(max_path, path);
// strcat(max_path, "/max_brightness");

// strcat(path, "/brightness");

strcpy(path, "/sys/devices/platform/android-backlight.0/backlight/android-backlight.0/brightness");
strcpy(max_path, "/sys/devices/platform/android-backlight.0/backlight/android-backlight.0/max_brightness");
LOGI("max backlight file is %s\n", max_path);
LOGI("backlight brightness file is %s\n", path);

status = 0;
}

/* todo other lights device init */
return status;
}

[cpp]
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LOCAL_PATH := $(call my-dir)

# HAL module implemenation, not prelinked and stored in hw/

include $(CLEAR_VARS)
LOCAL_MODULE_TAGS := optional
LOCAL_PRELINK_MODULE := false
LOCAL_MODULE_PATH := $(TARGET_OUT_SHARED_LIBRARIES)/hw
LOCAL_SHARED_LIBRARIES := liblog libcutils
LOCAL_SRC_FILES := android_light.c
LOCAL_MODULE := lights.default
#LOCAL_MODULE_TAGS := eng

include $(BUILD_SHARED_LIBRARY)

LOCAL_PATH := $(call my-dir)

# HAL module implemenation, not prelinked and stored in hw/
include $(CLEAR_VARS)
LOCAL_MODULE_TAGS := optional
LOCAL_PRELINK_MODULE := false
LOCAL_MODULE_PATH := $(TARGET_OUT_SHARED_LIBRARIES)/hw
LOCAL_SHARED_LIBRARIES := liblog libcutils
LOCAL_SRC_FILES := android_light.c
LOCAL_MODULE := lights.default
#LOCAL_MODULE_TAGS := eng
include $(BUILD_SHARED_LIBRARY)

这里我要声明的是，在读写之前先把文件的权限打开，在init.rc中去做

[cpp]
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#add by Jay
chmod 777 /sys/bus/iio/devices/device0/lux
chmod 777 /sys/bus/iio/devices/device1/value
chmod 777 /sys/bus/iio/devices/device1/active
chmod 777 /sys/class/backlight/android-backlight.0/brightness
chmod 777 /sys/class/backlight/android-backlight.0/max_brightness

#add by Jay
chmod 777 /sys/bus/iio/devices/device0/lux
chmod 777 /sys/bus/iio/devices/device1/value
chmod 777 /sys/bus/iio/devices/device1/active
chmod 777 /sys/class/backlight/android-backlight.0/brightness
chmod 777 /sys/class/backlight/android-backlight.0/max_brightness

好了，hal层我们就添加到这边，我们来重新编译，然后打开我们的模拟器，

打开setting中的display，然后调节屏幕亮度，然后再cat brightness会发现节点中的值改变了



把亮度调到最高，值变成了255.

结束！！！！下面会分析android framework中jni去实现lightService。