virtcon.txt

vc_display_init()
    open("/dev/class/display-controller/000/virtcon", O_RDWR)

handle_display_changed   
    handle_display_added()
        create_layer()

    rebind_display()
        任选一个display, 在后面Controller::ApplyConfiguration里，
        如果device id对不上会跳过


        allocate_vmo(size, &vmo)

        import_vmo(display, vmo, &image_id)
            i915.cpp
            Controller::ImportVmoImage(image_t* image, const zx::vmo& vmo, size_t offset)
                width_in_tiles(image->type, image->width, image->pixel_format)
                gtt_.AllocRegion(length, align, &gtt_region);
                    分配一个gtt region
                gtt_region->PopulateRegion(vmo.get(), offset / PAGE_SIZE, length);
                    把vmo对应的内存commit并且固定下来。
                    把gtt页表项设置好，也就是把graphics虚拟内存对应到vmo的物理地址上

        set_display_layer(info->id, info->layer_id)


        configure_layer(display, layer_id)
            
            setprimarylayerconfig
            Client::HandleSetLayerPrimaryConfig
                populate_image(req->image_config, &primary_layer->image);
            设置这个layer的primary config

            SetLayerPrimaryPosition

            SetLayerImage

        apply_configuration()

            Client::HandleCheckConfig
                没有实质性动作

            Client::HandleApplyConfig
                layer_node.layer->pending_image_->PrepareFences(
                            GetFence(layer->pending_wait_event_id_),
                            GetFence(layer->pending_signal_event_id_));
                            这里应该都是null
                ApplyConfig();
                    controller_->ApplyConfig(dc_configs, dc_idx, is_vc_, client_apply_count_);
                        image->StartPresent();
                        ops_.ops->apply_configuration(ops_.ctx, display_configs, display_count);
                            ReallocatePlaneBuffers(display_config, display_count)
                                GetPlaneLayer(pipe, plane_num, display_configs, display_count, &layer)
                                    拿到相应的layer
                                UpdateAllocations(min_allocs, data_rate);
                            
                            display->ApplyConfiguration(config, &regs);
                                ConfigurePrimaryPlane(plane, primary, !!config->cc_flags, &scaler_1_claimed, regs);
                                    base_address = static_cast<uint32_t>(region->base());
                                    plane_surface.set_surface_base_addr(base_address >> plane_surface.kRShiftCount);