We have been debugging an issue where the HDMI interface of the iMX8MP is connected to a LT6711A HDMI to display port converter and sometimes the monitor fails to be initialized after a cable connection / disconnection cycle.
The HPD output of the Lontium chip is connected to the HPD input of the iMX8MP, and this HPD pin is manipulated independently of the fact of having a cable connected. In fact, in this application, the "cable" will be traces on the PCB, so there will always be a "cable" connection independently of the HPD pin state. Our customer measured the HDMI signals when the HPD line is being manipulated, and found that when the HPD is on the "disconnected" state, there are still signals on both the HDMI clock and data lines.
We can reproduce this issue on our side by using a jumper and manipulating the HPD pin between on and off states.
On the following picture we can see an event where I changed the HPD pin to the disconnected state. We can see that the clock signal turns off for a while, and then starts back on without any other action on my side:
The customer reported to us that these signals could be negatively affecting the Lontium chip and causing connection failures sometimes. For us to validate this assumption, we would like to disable the RXSENSE functionality of the HDMI port so that we can guarantee no signals are being put on the clock and data lines when the HPD pin says the cable is disconnected.
Is there a way to completely disable the RXSENSE feature?
Apart from the RXSENSE feature, what else could be causing signals to be present on the HDMI pins when the HPD pin says the cable is not present?
Thanks for the help,
Rafael
