As its name suggests, a HwVidStartIO function is the entry point for incoming video requests for the miniport driver to process on the adapter. HwVidStartIO is called with pointers to a VRP and to the miniport’s per-adapter device extension.
After the corresponding display driver has a handle for the miniport’s adapter, all of the VRPs sent to the HwVidStartIO function have the IoControlCode field set to an IOCTL_VIDEO_XXX. On receipt of such a request, the HwVidStartIO function does the following:
The video port driver sets up VRPs and serializes calls to the HwVidStartIO function, which owns each input VRP until the miniport driver completes the requested operation and returns control. Every HwVidStartIO function must set status in each VRP and return a Boolean TRUE, indicating that each input request was processed.