The system-supplied video port driver sends all requests that originate in the display driver’s call to EngDeviceIoControl to the corresponding miniport driver as VRPs. The video port driver maps incoming IRPs to VRPs and calls the miniport driver with a pointer to each VIDEO_REQUEST_PACKET structure that it sets up.
The video port driver also manages the synchronization of incoming requests for all video miniport drivers by sending each miniport only one VRP for processing at a time. Until a miniport driver completes the current VRP, the video port driver holds on to any outstanding IRPs that the I/O Manager sent in response to the corresponding display driver’s call to EngDeviceIoControl.