void InputReader::processEventsLocked(const RawEvent* rawEvents, size_t count) {
    for (const RawEvent* rawEvent = rawEvents; count;) {
        int32_t type = rawEvent->type;
        size_t batchSize = 1;
        if (type < EventHubInterface::FIRST_SYNTHETIC_EVENT) {
            int32_t deviceId = rawEvent->deviceId;
            // 獲取同一個設(shè)備的元輸入事件的數(shù)量
            while (batchSize < count) {
                if (rawEvent[batchSize].type >= EventHubInterface::FIRST_SYNTHETIC_EVENT ||
                    rawEvent[batchSize].deviceId != deviceId) {
                    break;
                }
                batchSize += 1;
            }
            // 批量處理同一個設(shè)備的元輸入事件
            processEventsForDeviceLocked(deviceId, rawEvent, batchSize);
        } else {
            // ...
        }
        count -= batchSize;
        rawEvent += batchSize;
    }
}
void InputReader::processEventsForDeviceLocked(int32_t eventHubId, const RawEvent* rawEvents,
                                               size_t count) {
    auto deviceIt = mDevices.find(eventHubId);
    if (deviceIt == mDevices.end()) {
        return;
    }
    std::shared_ptr<InputDevice>& device = deviceIt->second;
    // 如果 InputDevice 沒有 InputMapper，那么它不能處理事件
    if (device->isIgnored()) {
        return;
    }
    // InputDevice 批量處理元輸入事件
    device->process(rawEvents, count);
}

// frameworks/native/services/inputflinger/reader/InputDevice.cpp
void InputDevice::process(const RawEvent* rawEvents, size_t count) {
    // 雖然 InputReader 把批量的事件交給 InputDevice，但是 InputDevice 還是逐個處理事件
    for (const RawEvent* rawEvent = rawEvents; count != 0; rawEvent++) {
        if (mDropUntilNextSync) {
            if (rawEvent->type == EV_SYN && rawEvent->code == SYN_REPORT) {
                mDropUntilNextSync = false;
            } 
        } else if (rawEvent->type == EV_SYN && rawEvent->code == SYN_DROPPED) {
            // EV_SYN + SYN_DROPPED 表明要丟棄后面的事件，直到 EV_SYN + SYN_REPORT
            mDropUntilNextSync = true;
            reset(rawEvent->when);
        } else {
            // 每一個事件交給 InputMapper 處理
            for_each_mapper_in_subdevice(rawEvent->deviceId, [rawEvent](InputMapper& mapper) {
                mapper.process(rawEvent);
            });
        }
        --count;
    }
}

void KeyboardInputMapper::process(const RawEvent* rawEvent) {
    switch (rawEvent->type) {
        // 處理 EV_KEY
        case EV_KEY: {
            int32_t scanCode = rawEvent->code;
            int32_t usageCode = mCurrentHidUsage;
            mCurrentHidUsage = 0;
            if (isKeyboardOrGamepadKey(scanCode)) {
                // 注意第三個參數(shù)，value等于0，才表示按鍵down， 也就是說，value 為1， 表示按鍵被按下
                processKey(rawEvent->when, rawEvent->readTime, rawEvent->value != 0, scanCode,
                           usageCode);
            }
            break;
        }
        case EV_MSC: {
            // ...
        }
        // 處理 EV_SYN + SYN_REPORT
        case EV_SYN: {
            if (rawEvent->code == SYN_REPORT) {
                mCurrentHidUsage = 0;
            }
        }
    }
}

void KeyboardInputMapper::processKey(nsecs_t when, nsecs_t readTime, bool down, int32_t scanCode,
                                     int32_t usageCode) {
    int32_t keyCode;
    int32_t keyMetaState;
    uint32_t policyFlags;
    // 1. 根據(jù)鍵盤配置文件，把 scanCode 轉(zhuǎn)化為 keycode，并獲取 flags
    if (getDeviceContext().mapKey(scanCode, usageCode, mMetaState, &keyCode, &keyMetaState,
                                  &policyFlags)) {
        keyCode = AKEYCODE_UNKNOWN;
        keyMetaState = mMetaState;
        policyFlags = 0;
    }
    // 按下
    if (down) {
        // 根據(jù)屏幕方向，再次轉(zhuǎn)換 keyCode
        // Rotate key codes according to orientation if needed.
        if (mParameters.orientationAware) {
            keyCode = rotateKeyCode(keyCode, getOrientation());
        }
        // Add key down.
        ssize_t keyDownIndex = findKeyDown(scanCode);
        if (keyDownIndex >= 0) {
            // key repeat, be sure to use same keycode as before in case of rotation
            keyCode = mKeyDowns[keyDownIndex].keyCode;
        } else {
            // key down
            if ((policyFlags & POLICY_FLAG_VIRTUAL) &&
                getContext()->shouldDropVirtualKey(when, keyCode, scanCode)) {
                return;
            }
            if (policyFlags & POLICY_FLAG_GESTURE) {
                // 如果設(shè)備通知支持觸摸，那么發(fā)送一個 ACTION_CANCEL 事件
                getDeviceContext().cancelTouch(when, readTime);
            }
            KeyDown keyDown;
            keyDown.keyCode = keyCode;
            keyDown.scanCode = scanCode;
            // 保存按下的按鍵
            mKeyDowns.push_back(keyDown);
        }
        mDownTime = when;
    } else { // 抬起按鍵
        // Remove key down.
        ssize_t keyDownIndex = findKeyDown(scanCode);
        if (keyDownIndex >= 0) {
            // key up, be sure to use same keycode as before in case of rotation
            keyCode = mKeyDowns[keyDownIndex].keyCode;
            // 移除
            mKeyDowns.erase(mKeyDowns.begin() + (size_t)keyDownIndex);
        } else {
            // key was not actually down
            ALOGI("Dropping key up from device %s because the key was not down.  "
                  "keyCode=%d, scanCode=%d",
                  getDeviceName().c_str(), keyCode, scanCode);
            return;
        }
    }
    // 更新meta狀態(tài)
    if (updateMetaStateIfNeeded(keyCode, down)) {
        // If global meta state changed send it along with the key.
        // If it has not changed then we'll use what keymap gave us,
        // since key replacement logic might temporarily reset a few
        // meta bits for given key.
        keyMetaState = mMetaState;
    }
    nsecs_t downTime = mDownTime;
    // 外部設(shè)備的按鍵按下時，添加喚醒標(biāo)志位
    if (down && getDeviceContext().isExternal() && !mParameters.doNotWakeByDefault &&
        !isMediaKey(keyCode)) {
        policyFlags |= POLICY_FLAG_WAKE;
    }
    // 設(shè)備是否能生成重復(fù)按鍵事件，一般設(shè)備都不支持這個功能
    // 而是由系統(tǒng)模擬生成重復(fù)按鍵事件
    if (mParameters.handlesKeyRepeat) {
        policyFlags |= POLICY_FLAG_DISABLE_KEY_REPEAT;
    }
    // 2. 生成 NotifyKeyArgs, 并加到 QueuedInputListener 隊列中
    NotifyKeyArgs args(getContext()->getNextId(), when, readTime, getDeviceId(), mSource,
                       getDisplayId(), policyFlags,
                       down ? AKEY_EVENT_ACTION_DOWN : AKEY_EVENT_ACTION_UP/*action*/,
                       AKEY_EVENT_FLAG_FROM_SYSTEM/*flags*/, keyCode, scanCode, keyMetaState, downTime);
    getListener()->notifyKey(&args);
}

status_t EventHub::mapKey(int32_t deviceId, int32_t scanCode, int32_t usageCode, int32_t metaState,
                          int32_t* outKeycode, int32_t* outMetaState, uint32_t* outFlags) const {
    std::scoped_lock _l(mLock);
    Device* device = getDeviceLocked(deviceId);
    status_t status = NAME_NOT_FOUND;
    if (device != nullptr) {
        // Check the key character map first.
        const std::shared_ptr<KeyCharacterMap> kcm = device->getKeyCharacterMap();
        if (kcm) {
            // 1. KeyCharacterMapFile :轉(zhuǎn)換 scanCode 為 keyCode
            if (!kcm->mapKey(scanCode, usageCode, outKeycode)) {
                *outFlags = 0;
                status = NO_ERROR;
            }
        }
        // Check the key layout next.
        if (status != NO_ERROR && device->keyMap.haveKeyLayout()) {
            // 2. KeyLayoutFile: 把 scanCode 轉(zhuǎn)換為 keycode
            if (!device->keyMap.keyLayoutMap->mapKey(scanCode, usageCode, outKeycode, outFlags)) {
                status = NO_ERROR;
            }
        }
        if (status == NO_ERROR) {
            if (kcm) {
                // 3. KeyCharacterMapFile: 根據(jù)meta按鍵狀態(tài)，重新映射按鍵字符
                kcm->tryRemapKey(*outKeycode, metaState, outKeycode, outMetaState);
            } else {
                *outMetaState = metaState;
            }
        }
    }
    if (status != NO_ERROR) {
        *outKeycode = 0;
        *outFlags = 0;
        *outMetaState = metaState;
    }
    return status;
}

    6: qpnp_pon
      Classes: KEYBOARD
      Path: /dev/input/event0
      Enabled: true
      Descriptor: fb60d4f4370f5dbe8267b63d38dea852987571ab
      Location: qpnp_pon/input0
      ControllerNumber: 0
      UniqueId: 
      Identifier: bus=0x0000, vendor=0x0000, product=0x0000, version=0x0000
      KeyLayoutFile: /system/usr/keylayout/Generic.kl
      KeyCharacterMapFile: /system/usr/keychars/Generic.kcm
      ConfigurationFile: 
      VideoDevice: <none>

key 116   POWER

// frameworks/native/include/android/keycodes.h
/**
 * Key codes.
 */
enum {
AKEYCODE_POWER = 26,
}

// frameworks/base/core/java/android/view/KeyEvent.java
public static final int KEYCODE_POWER           = 26;

key 116   POWER WAKE