I am using below reference code in the CUI Doc to read out DPCD register data from a DP-VGA dongle which is connected to the downstream port of DP MST Hub (PC -> DP MST Hub -> DP-VGA dongle).
DWORD dwError = 0;
InData.relativeAddress.ucTotalLinkCount = pDisplays->relativeAddress.ucTotalLinkCount;
InData.relativeAddress.ucAddress = pDisplays->relativeAddress.ucAddress;
InData.portType = pDPTopology-> PortList;
InData.dwOpType = IGFX_REMOTE_AUX_READ;
InData.dwSize = 5;
InData.dwAddress = 0x500;
hr = pCUIExternal8->GetDeviceData((GUID*)&IGFX_GET_SET_REMOTE_AUX_INFO_GUID, sizeof(InData), (BYTE*)&InData, &dwError);
I could see DP MST Hub reading 5 byes DPCD register data from DP-VGA dongle at DPCD register address 0x500 by using DP AUX analyzer and received hr = OK from API call, however the reading back DPCD register data is not stored in the data buffer (InData.Data). InData.Data -  has all "0" data.
Any comment to solve the issue would be very appreciated.
I understand you are trying to read out DPCD register data from a DP-VGA dongle.
Let me apologize for any inconvenience this issue may be causing to you.
I recommend contacting our graphics developers so they can assist you better. You can post your inquiry on this forum https://software.intel.com/en-us/forums/developing-games-and-graphics-on-intel https://software.intel.com/en-us/forums/developing-games-and-graphics-on-intel