安卓hal背光驱动分析

一、背光驱动HAL层分析

1.源文件目录：

android-4.1.2/device/friendly-arm/common/liblight/lights.c

2.源代码节选：

static pthread_once_t g_init = PTHREAD_ONCE_INIT;
static pthread_mutex_t g_lock = PTHREAD_MUTEX_INITIALIZER;

#define LIGHTS_HARDWARE_MODULE_ID "lights"
char const *const LCD_FILE = "/sys/class/backlight/pwm-backlight.0/brightness";/*回归linux一切皆文件的本质，其实安卓驱动也是通过打开linux的设备文件或者sys文件，然后通过读写文件来达到控制硬件的目的*/

/*往背光驱动的设备文件写入亮度值*/
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;
    }
}

/*设置背光的颜色值*/
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;
}

/*设置背光亮度*/
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;
}

/*关闭背光驱动*/
static int close_lights(struct light_device_t *dev)
{
    LOGV("close_light is called");
    if (dev)
        free(dev);

    return 0;
}

/*打开背光驱动，实质是把背光驱动的接口提交给上层调用（填充hw_device_t结构体）*/
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);

    LOGV("open_lights: open with %s", name);

    if (0 == strcmp(LIGHT_ID_BACKLIGHT, name))
        set_light = set_light_backlight;
    else
        return -EINVAL;

    pthread_mutex_init(&g_lock, NULL);

    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;
}

/*定义hal层的背光控制的open接口*/
static struct hw_module_methods_t lights_module_methods = {
    .open =  open_lights,
};
/*hal的符号列表，当打开动态链接库“.so”的时候，是通过id来索引或者识别该模块的*/
/*const */ struct hw_module_t HAL_MODULE_INFO_SYM = {
    .tag = HARDWARE_MODULE_TAG,
    .version_major = 1,
    .version_minor = 0,
    .id = LIGHTS_HARDWARE_MODULE_ID,/*这个id是链接上层接口的关键点*/
    .name = "lights Module",
    .author = "Google, Inc.",
    .methods = &lights_module_methods,
};

二、背光驱动JNI层分析

1、源文件目录：

frameworks/base/services/jni/com_android_server_LightsService.cpp

2.源代码节选

namespace android
{

// These values must correspond with the LIGHT_ID constants in
// LightsService.java
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_INDEX_BLUETOOTH = 6,
    LIGHT_INDEX_WIFI = 7,
    LIGHT_COUNT
};

struct Devices {
    light_device_t* lights[LIGHT_COUNT];
};

static light_device_t* get_device(hw_module_t* module, char const* name)
{
    int err;
    hw_device_t* device;
    err = module->methods->open(module, name, &device);
    if (err == 0) {
        return (light_device_t*)device;
    } else {
        return NULL;
    }
}

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);
        devices->lights[LIGHT_INDEX_BLUETOOTH]
                = get_device(module, LIGHT_ID_BLUETOOTH);
        devices->lights[LIGHT_INDEX_WIFI]
                = get_device(module, LIGHT_ID_WIFI);
    } else {
        memset(devices, 0, sizeof(Devices));
    }

    return (jint)devices;
}

static void finalize_native(JNIEnv *env, jobject clazz, int ptr)
{
    Devices* devices = (Devices*)ptr;
    if (devices == NULL) {
        return;
    }

    free(devices);
}

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);
}

static JNINativeMethod method_table[] = {
    { "init_native", "()I", (void*)init_native },
    { "finalize_native", "(I)V", (void*)finalize_native },
    { "setLight_native", "(IIIIIII)V", (void*)setLight_native },
};

int register_android_server_LightsService(JNIEnv *env)
{
    return jniRegisterNativeMethods(env, "com/android/server/LightsService",
            method_table, NELEM(method_table));
}

};

三、背光驱动service层分析

1.源码目录：

frameworks/base/services/java/com/android/server/LightsService.java

2.源码节选：

public class LightsService {
    private static final String TAG = "LightsService";
    private static final boolean DEBUG = false;

    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;
    static final int LIGHT_ID_BLUETOOTH = 6;
    static final int LIGHT_ID_WIFI = 7;
    static final int LIGHT_ID_COUNT = 8;

    static final int LIGHT_FLASH_NONE = 0;
    static final int LIGHT_FLASH_TIMED = 1;
    static final int LIGHT_FLASH_HARDWARE = 2;

    /**
     * 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;

    private final Light mLights[] = new Light[LIGHT_ID_COUNT];

    public final class Light {

        private Light(int id) {
            mId = id;
        }

        public void setBrightness(int brightness) {
            setBrightness(brightness, BRIGHTNESS_MODE_USER);
        }

        public void setBrightness(int brightness, int brightnessMode) {
            synchronized (this) {
                int color = brightness & 0x000000ff;
                color = 0xff000000 | (color << 16) | (color << 8) | color;
                setLightLocked(color, LIGHT_FLASH_NONE, 0, 0, brightnessMode);
            }
        }

        public void setColor(int color) {
            synchronized (this) {
                setLightLocked(color, LIGHT_FLASH_NONE, 0, 0, 0);
            }
        }

        public void setFlashing(int color, int mode, int onMS, int offMS) {
            synchronized (this) {
                setLightLocked(color, mode, onMS, offMS, BRIGHTNESS_MODE_USER);
            }
        }


        public void pulse() {
            pulse(0x00ffffff, 7);
        }

        public void pulse(int color, int onMS) {
            synchronized (this) {
                if (mColor == 0 && !mFlashing) {
                    setLightLocked(color, LIGHT_FLASH_HARDWARE, onMS, 1000, BRIGHTNESS_MODE_USER);
                    mH.sendMessageDelayed(Message.obtain(mH, 1, this), onMS);
                }
            }
        }

        public void turnOff() {
            synchronized (this) {
                setLightLocked(0, LIGHT_FLASH_NONE, 0, 0, 0);
            }
        }

        private void stopFlashing() {
            synchronized (this) {
                setLightLocked(mColor, LIGHT_FLASH_NONE, 0, 0, BRIGHTNESS_MODE_USER);
            }
        }

        private void setLightLocked(int color, int mode, int onMS, int offMS, int brightnessMode) {
            if (color != mColor || mode != mMode || onMS != mOnMS || offMS != mOffMS) {
                if (DEBUG) Slog.v(TAG, "setLight #" + mId + ": color=#"
                        + Integer.toHexString(color));
                mColor = color;
                mMode = mode;
                mOnMS = onMS;
                mOffMS = offMS;
                setLight_native(mNativePointer, mId, color, mode, onMS, offMS, brightnessMode);
            }
        }

        private int mId;
        private int mColor;
        private int mMode;
        private int mOnMS;
        private int mOffMS;
        private boolean mFlashing;
    }

    /* This class implements an obsolete API that was removed after eclair and re-added during the
     * final moments of the froyo release to support flashlight apps that had been using the private
     * IHardwareService API. This is expected to go away in the next release.
     */
    private final IHardwareService.Stub mLegacyFlashlightHack = new IHardwareService.Stub() {

        private static final String FLASHLIGHT_FILE = "/sys/class/leds/spotlight/brightness";

        public boolean getFlashlightEnabled() {
            try {
                FileInputStream fis = new FileInputStream(FLASHLIGHT_FILE);
                int result = fis.read();
                fis.close();
                return (result != '0');
            } catch (Exception e) {
                return false;
            }
        }

        public void setFlashlightEnabled(boolean on) {
            if (mContext.checkCallingOrSelfPermission(android.Manifest.permission.FLASHLIGHT)
                    != PackageManager.PERMISSION_GRANTED &&
                    mContext.checkCallingOrSelfPermission(android.Manifest.permission.HARDWARE_TEST)
                    != PackageManager.PERMISSION_GRANTED) {
                throw new SecurityException("Requires FLASHLIGHT or HARDWARE_TEST permission");
            }
            try {
                FileOutputStream fos = new FileOutputStream(FLASHLIGHT_FILE);
                byte[] bytes = new byte[2];
                bytes[0] = (byte)(on ? '1' : '0');
                bytes[1] = '\n';
                fos.write(bytes);
                fos.close();
            } catch (Exception e) {
                // fail silently
            }
        }
    };

    LightsService(Context context) {

        mNativePointer = init_native();
        mContext = context;

        ServiceManager.addService("hardware", mLegacyFlashlightHack);

        for (int i = 0; i < LIGHT_ID_COUNT; i++) {
            mLights[i] = new Light(i);
        }
    }

    protected void finalize() throws Throwable {
        finalize_native(mNativePointer);
        super.finalize();
    }

    public Light getLight(int id) {
        return mLights[id];
    }

    private Handler mH = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            Light light = (Light)msg.obj;
            light.stopFlashing();
        }
    };

    private static native int init_native();
    private static native void finalize_native(int ptr);

    private static native void setLight_native(int ptr, int light, int color, int mode,
            int onMS, int offMS, int brightnessMode);

    private final Context mContext;

    private int mNativePointer;
}

3.安卓系统和背光驱动的关联

安卓系统的背光驱动其实和电池管理系统是合在一起管理的。
在源文件:

frameworks/base/services/java/com/android/server/SystemServer.java

源码节选如下：

Slog.i(TAG, "Lights Service");
lights = new LightsService(context);
Slog.i(TAG, "Battery Service");
battery = new BatteryService(context, lights);
ServiceManager.addService("battery", battery);