TMDS181: TMDS181 no signal issue

Hi Team,

My customer is using TMDS181 and found some issues.

TMDS181 is used for HDMI OUT output, issues are:

1. when setting the HDMI OUT output to 4K resolution and after the host restarts, if doing HDMI cable plug and unplug operations, there is a probability of no signal (no picture in the display);
2. If setting the HDMI OUT output to 1080P resolution, the signal is good. And then resetting it to 4K resolution, the host restarts with HDMI OUT being connected to HDMI cable, the signal is good.

During the debug process, customer found that:

1. When doing HDMI cable plug and unplug operations in 4K resolution case, there has probability that HPD_SRC can be pulled up twice by the slave. In the second time of HPD being pulled high, the host doesn’t re-read the EDID of the slave.
2. For 4K resolution case, when the HPD_SRC is pulled up for the second time by the slave, the front-end TMDS signal of TMDS181 continues to exist, while the back-end TMDS signal of TMDS181 disappears. And if pulling up again, there has no signal in the display. For 1080P resolution case, in the second time of HPD being pulled high, the host doesn’t re-read the EDID of the slave, but the signal is good.
3. HPD_SRC is pulled up after the slave display being connected, while HPD_SNK always keeps 3.3V high.

Based on above info, Could you help confirm the following two questions:

1. Why there has no signal in 4K resolution, but 1080P is good?
2. In 4K resolution case, why the signal is good if the HDMI cable is connected before the host’s start-up, but there is a probability of no signal if doing HDMI cable plug and unplug operations after the host’s start-up?

Best regards,

Yang