Android 12(S) 图像显示系统 – HWC HAL 初始化与调用流程
- 2022 年 6 月 28 日
- 筆記
- Android 图形图像, Android图形图像
必读：
Android 12(S) 图像显示系统 – 开篇
接口定义
源码位置：/hardware/interfaces/graphics/composer/
在源码目录下可以看到4个版本的HIDL Interface定义，最新版本是2.4，也是目前我的测试平台在用的，不同版本使用带有版本号的包名来区分，例如 ：package [email protected]
各版本中均有相同的接口，并且具有继承关系，新版本继承旧版接口并扩展了新方法。
/frameworks/native/services/surfaceflinger/DisplayHardware/ 中 android::Hwc2::impl::Composer 相当于HIDL的客户端，framework通过impl::Composer中的方法看跨进程和 hwc hal 互动。
各个版本接口的继承关系
Composer HIDL Service
代码位置
/hardware/interfaces/graphics/composer/2.4/default/service.cpp
/hardware/interfaces/graphics/composer/2.4/default/[email protected]
开机启动时，init进程解析rc文件带起服务进程，在service.cpp的main函数中，注册服务
int main() {
...
android::sp<IComposer> composer = HwcLoader::load();
if (composer == nullptr) {
return 1;
}
if (composer->registerAsService() != android::NO_ERROR) {
ALOGE("failed to register service");
return 1;
}
...
}
可以看到其中调用了一个非常重要的方法HwcLoader::load()，看其代码：
[/hardware/interfaces/graphics/composer/2.4/utils/passthrough/include/composer-passthrough/2.4/HwcLoader.h]
static IComposer* load() {
const hw_module_t* module = loadModule();
if (!module) {
return nullptr;
}
auto hal = createHalWithAdapter(module);
if (!hal) {
return nullptr;
}
return createComposer(std::move(hal)).release();
}
再看loadModule的定义，去找HAL library中定义的HAL_MODULE_INFO_SYM结构体变量
[/hardware/interfaces/graphics/composer/2.1/utils/passthrough/include/composer-passthrough/2.1/HwcLoader.h]
static const hw_module_t* loadModule() {
const hw_module_t* module;
int error = hw_get_module(HWC_HARDWARE_MODULE_ID, &module);
if (error) {
ALOGI("falling back to gralloc module");
error = hw_get_module(GRALLOC_HARDWARE_MODULE_ID, &module);
}
if (error) {
ALOGE("failed to get hwcomposer or gralloc module");
return nullptr;
}
return module;
}
可以看到基本的调用流程：
开机启动 ==> HwcLoader::load() ==> HwcLoader::loadModule() ==> hw_get_module
hw_get_module就是去打开Vendor厂商实现的HWC HAL模块，这个流程本质上还是旧有的HAL打开方式，只是外包装了一层HIDL。
最终得到一个指向HWC module的hw_module_t指针
再回到HwcLoader::load()方法中，接下来就是 createHalWithAdapter ==> createComposer
先看 createHalWithAdapter 做了哪些工作
[/hardware/interfaces/graphics/composer/2.4/utils/passthrough/include/composer-passthrough/2.4/HwcLoader.h]
// create a ComposerHal instance, insert an adapter if necessary
static std::unique_ptr<hal::ComposerHal> createHalWithAdapter(const hw_module_t* module) {
bool adapted;
hwc2_device_t* device = openDeviceWithAdapter(module, &adapted);
if (!device) {
return nullptr;
}
auto hal = std::make_unique<HwcHal>();
return hal->initWithDevice(std::move(device), !adapted) ? std::move(hal) : nullptr;
}
其中调用了openDeviceWithAdapter去打开 hwc2_device_t
[/hardware/interfaces/graphics/composer/2.1/utils/passthrough/include/composer-passthrough/2.1/HwcLoader.h]
// open hwcomposer2 device, install an adapter if necessary
static hwc2_device_t* openDeviceWithAdapter(const hw_module_t* module, bool* outAdapted) {
if (module->id && std::string(module->id) == GRALLOC_HARDWARE_MODULE_ID) {
*outAdapted = true;
return adaptGrallocModule(module);
}
hw_device_t* device;
int error = module->methods->open(module, HWC_HARDWARE_COMPOSER, &device);
if (error) {
ALOGE("failed to open hwcomposer device: %s", strerror(-error));
return nullptr;
}
int major = (device->version >> 24) & 0xf;
if (major != 2) {
*outAdapted = true;
return adaptHwc1Device(std::move(reinterpret_cast<hwc_composer_device_1*>(device)));
}
*outAdapted = false;
return reinterpret_cast<hwc2_device_t*>(device);
}
openDeviceWithAdapter中调用了open方法
hw_device_t* device;
int error = module->methods->open(module, HWC_HARDWARE_COMPOSER, &device);
这样就获取到了 hwc2_device
typedef struct hwc2_device {
struct hw_device_t common;
void (*getCapabilities)(struct hwc2_device* device, uint32_t* outCount,
int32_t* /*hwc2_capability_t*/outCapabilities);
hwc2_function_pointer_t (*getFunction)(struct hwc2_device* device,
int32_t /*hwc2_function_descriptor_t*/descriptor);
} hwc2_device_t;
回到createHalWithAdapter中再调用initWithDevice及保存到了HwcHal中的mDevice这个变量中
bool initWithDevice(hwc2_device_t* device, bool requireReliablePresentFence) {
// we own the device from this point on
mDevice = device;
….
}getFunction函数关联到了 vendor 厂商实现的hwc hal中具体实现，这个函数通过函数描述符来获取对应的函数指针。
initDispatch的作用介绍
initDispatch()来初始化HWC通用的函数指针
2.4 <—2.3<—2.2<—2.1 版本的initDispatch()会被调用到来初始化函数指针
在这里就是把mDispatch函数指针和HWC HAL具体实现的方法一一对应起来
注意一下继承关系：
V2_1
class HwcHalImpl : public Hal
V2_2
class HwcHalImpl : public V2_1::passthrough::detail::HwcHalImpl<Hal>
V2_3
class HwcHalImpl : public V2_2::passthrough::detail::HwcHalImpl<Hal>
V2_4
class HwcHalImpl : public V2_3::passthrough::detail::HwcHalImpl<Hal>
各个版本的HwcHalImpl类中都有定义一个结构体变量mDispatch，这个结构体的成员变量均为函数指针,是以 HWC2_PFN_* 开头的函数指针类型。
struct {
HWC2_PFN_ACCEPT_DISPLAY_CHANGES acceptDisplayChanges;
HWC2_PFN_CREATE_LAYER createLayer;
……
HWC2_PFN_VALIDATE_DISPLAY validateDisplay;
} mDispatch = {};
initDispatch通过调用vendor厂商实现的hwc hal中的getFunction方法获取到descriptor对应的函数指针，并保存到mDispatch的成员中
template <typename T>
bool initDispatch(hwc2_function_descriptor_t desc, T* outPfn) {
auto pfn = mDevice->getFunction(mDevice, desc);
if (pfn) {
*outPfn = reinterpret_cast<T>(pfn);
return true;
} else {
ALOGE("failed to get hwcomposer2 function %d", desc);
return false;
}
}简单总结下上述的分析内容
1. 开机后启动了一个名字为[email protected]的服务进程，用于 framework 和 hwc hal 的通信；
2. 这个composer service启动时，进行了必要的初始化工作，主要就是loadModule和openDevice，在这一过程中获取到hal层实现的函数的指针，
并保存在了mDispatch中
3. 之后运行时，framework 呼叫功能时，本质就是通过mDispatch持有的函数指针调用到 hwc hal 的具体实现
Framework 与 hwc hal通信的流程
直接打印调用栈信息来展示这一流程，以其中的setClientTarget这个方法的调用过程为例：
SurfaceFlinger进程的调用栈信息
11-13 00:47:20.455 224 224 E HwcComposer: stackdump:#00 pc 00086f8f /system/bin/surfaceflinger (android::Hwc2::impl::Composer::setClientTarget(unsigned long long, unsigned int, android::sp<android::GraphicBuffer> const&, int, android::hardware::graphics::common::V1_2::Dataspace, std::__1::vector<android::hardware::graphics::composer::V2_1::IComposerClient::Rect, std::__1::allocator<android::hardware::graphics::composer::V2_1::IComposerClient::Rect> > const&)+182)
11-13 00:47:20.455 224 224 E HwcComposer: stackdump:#01 pc 00096791 /system/bin/surfaceflinger (android::impl::HWComposer::setClientTarget(android::HalDisplayId, unsigned int, android::sp<android::Fence> const&, android::sp<android::GraphicBuffer> const&, android::hardware::graphics::common::V1_2::Dataspace)+408)
11-13 00:47:20.455 224 224 E HwcComposer: stackdump:#02 pc 0008e881 /system/bin/surfaceflinger (android::FramebufferSurface::advanceFrame()+332)
11-13 00:47:20.455 224 224 E HwcComposer: stackdump:#03 pc 00122a55 /system/bin/surfaceflinger (android::compositionengine::impl::RenderSurface::queueBuffer(android::base::unique_fd_impl<android::base::DefaultCloser>)+436)
11-13 00:47:20.455 224 224 E HwcComposer: stackdump:#04 pc 001069ed /system/bin/surfaceflinger (android::compositionengine::impl::Output::finishFrame(android::compositionengine::CompositionRefreshArgs const&)+168)
11-13 00:47:20.455 224 224 E HwcComposer: stackdump:#05 pc 00100c89 /system/bin/surfaceflinger (android::compositionengine::impl::Display::finishFrame(android::compositionengine::CompositionRefreshArgs const&)+76)
11-13 00:47:20.455 224 224 E HwcComposer: stackdump:#06 pc 001054ef /system/bin/surfaceflinger (android::compositionengine::impl::Output::present(android::compositionengine::CompositionRefreshArgs const&)+114)
11-13 00:47:20.455 224 224 E HwcComposer: stackdump:#07 pc 000ff727 /system/bin/surfaceflinger (android::compositionengine::impl::CompositionEngine::present(android::compositionengine::CompositionRefreshArgs&)+146)
11-13 00:47:20.455 224 224 E HwcComposer: stackdump:#08 pc 000d600b /system/bin/surfaceflinger (android::SurfaceFlinger::onMessageRefresh()+1530)
11-13 00:47:20.455 224 224 E HwcComposer: stackdump:#09 pc 000d570d /system/bin/surfaceflinger (android::SurfaceFlinger::onMessageInvalidate(long long, long long)+8784)
11-13 00:47:20.455 224 224 E HwcComposer: stackdump:#10 pc 000b9907 /system/bin/surfaceflinger (android::impl::MessageQueue::Handler::handleMessage(android::Message const&)+94)
11-13 00:47:20.456 224 224 E HwcComposer: stackdump:#11 pc 00010179 /system/lib/libutils.so (android::Looper::pollInner(int)+288)
11-13 00:47:20.456 224 224 E HwcComposer: stackdump:#12 pc 0000ffff /system/lib/libutils.so (android::Looper::pollOnce(int, int*, int*, void**)+62)
11-13 00:47:20.456 224 224 E HwcComposer: stackdump:#13 pc 000b9dd1 /system/bin/surfaceflinger (android::impl::MessageQueue::waitMessage()+56)
11-13 00:47:20.456 224 224 E HwcComposer: stackdump:#14 pc 000cc50d /system/bin/surfaceflinger (android::SurfaceFlinger::run()+6)
11-13 00:47:20.456 224 224 E HwcComposer: stackdump:#15 pc 000ff253 /system/bin/surfaceflinger (main+1182)
11-13 00:47:20.456 224 224 E HwcComposer: stackdump:#16 pc 0003253b /apex/com.android.runtime/lib/bionic/libc.so (__libc_init+54)
HWC HAL端的调用栈信息
11-08 06:04:30.920 339 339 E hwc_display: stackdump:#00 pc 000287cb /vendor/lib/hw/hwcomposer.stark.so (Display::setClientTarget(native_handle const*, int, int, hwc_region)+90)
11-08 06:04:30.920 339 339 E hwc_display: stackdump:#01 pc 00023255 /vendor/lib/hw/hwcomposer.stark.so (hwc_setClientTarget(hwc2_device*, unsigned long long, native_handle const*, int, int, hwc_region)+56)
11-08 06:04:30.920 339 339 E hwc_display: stackdump:#02 pc 00007d93 /vendor/bin/hw/[email protected] (android::hardware::graphics::composer::V2_1::passthrough::detail::HwcHalImpl<android::hardware::graphics::composer::V2_4::hal::ComposerHal>::setClientTarget(unsigned long long, native_handle const*, int, int, std::__1::vector<hwc_rect, std::__1::allocator<hwc_rect> > const&)+40)
11-08 06:04:30.920 339 339 E hwc_display: stackdump:#03 pc 00010b11 /vendor/bin/hw/[email protected] (android::hardware::graphics::composer::V2_1::hal::ComposerCommandEngine::executeSetClientTarget(unsigned short)+244)
11-08 06:04:30.920 339 339 E hwc_display: stackdump:#04 pc 0000ed3f /vendor/bin/hw/[email protected] (android::hardware::graphics::composer::V2_1::hal::ComposerCommandEngine::execute(unsigned int, android::hardware::hidl_vec<android::hardware::hidl_handle> const&, bool*, unsigned int*, android::hardware::hidl_vec<android::hardware::hidl_handle>*)+86)
11-08 06:04:30.920 339 339 E hwc_display: stackdump:#05 pc 0000d0a1 /vendor/bin/hw/[email protected] (android::hardware::graphics::composer::V2_1::hal::detail::ComposerClientImpl<android::hardware::graphics::composer::V2_3::IComposerClient, android::hardware::graphics::composer::V2_3::hal::ComposerHal>::executeCommands(unsigned int, android::hardware::hidl_vec<android::hardware::hidl_handle> const&, std::__1::function<void (android::hardware::graphics::composer::V2_1::Error, bool, unsigned int, android::hardware::hidl_vec<android::hardware::hidl_handle> const&)>)+84)
11-08 06:04:30.920 339 339 E hwc_display: stackdump:#06 pc 0001df97 /vendor/lib/[email protected] (android::hardware::graphics::composer::V2_2::BnHwComposerClient::_hidl_executeCommands_2_2(android::hidl::base::V1_0::BnHwBase*, android::hardware::Parcel const&, android::hardware::Parcel*, std::__1::function<void (android::hardware::Parcel&)>)+294)
11-08 06:04:30.920 339 339 E hwc_display: stackdump:#07 pc 0003182f /vendor/lib/[email protected] (android::hardware::graphics::composer::V2_4::BnHwComposerClient::onTransact(unsigned int, android::hardware::Parcel const&, android::hardware::Parcel*, unsigned int, std::__1::function<void (android::hardware::Parcel&)>)+1198)
11-08 06:04:30.920 339 339 E hwc_display: stackdump:#08 pc 000546d9 /apex/com.android.vndk.v31/lib/libhidlbase.so (android::hardware::BHwBinder::transact(unsigned int, android::hardware::Parcel const&, android::hardware::Parcel*, unsigned int, std::__1::function<void (android::hardware::Parcel&)>)+96)
11-08 06:04:30.920 339 339 E hwc_display: stackdump:#09 pc 000536a7 /apex/com.android.vndk.v31/lib/libhidlbase.so (android::hardware::IPCThreadState::getAndExecuteCommand()+974)
11-08 06:04:30.920 339 339 E hwc_display: stackdump:#10 pc 00053239 /apex/com.android.vndk.v31/lib/libhidlbase.so (android::hardware::IPCThreadState::joinThreadPool(bool)+56)
11-08 06:04:30.920 339 339 E hwc_display: stackdump:#11 pc 000070fb /vendor/bin/hw/[email protected] (main+270)
11-08 06:04:30.920 339 339 E hwc_display: stackdump:#12 pc 0003253b /apex/com.android.runtime/lib/bionic/libc.so (__libc_init+54)
发起端：
[/frameworks/native/services/surfaceflinger/DisplayHardware/ComposerHal.cpp]
Error Composer::setClientTarget(Display display, uint32_t slot,
const sp<GraphicBuffer>& target,
int acquireFence, Dataspace dataspace,
const std::vector<IComposerClient::Rect>& damage)
{
mWriter.selectDisplay(display);
const native_handle_t* handle = nullptr;
if (target.get()) {
handle = target->getNativeBuffer()->handle;
}
mWriter.setClientTarget(slot, handle, acquireFence, dataspace, damage);
return Error::NONE;
}
中转站：
[/hardware/interfaces/graphics/composer/2.1/utils/command-buffer/include/composer-command-buffer/2.1/ComposerCommandBuffer.h]
void setClientTargetInternal(...) {
beginCommand(IComposerClient::Command::SET_CLIENT_TARGET, length);
...
endCommand();
}
跨进程了
[/hardware/interfaces/graphics/composer/2.1/utils/hal/include/composer-hal/2.1/ComposerCommandEngine.h]
virtual bool executeCommand(IComposerClient::Command command, uint16_t length) {
switch (command) {
...
case IComposerClient::Command::SET_CLIENT_TARGET:
return executeSetClientTarget(length);
}
}
bool executeSetClientTarget(uint16_t length) {
...
err = mHal->setClientTarget(mCurrentDisplay, clientTarget, fence, dataspace, damage);
...
}
处理终端：
Vendor厂商实现的HAL，具体实现setClientTarget的功能
