Change HDMI capabilities

I’m working on a device based on the Jetson Nano, that needs to be able to connect to many different kinds of monitors. It also runs through an HDMI isolator that, while passing metadata like EDID through unmodified, limits bandwidth to HDMI 1.3a. Since the nano is capable of higher bandwidth than that, and advertises as much, it negotiates frame rates and resolutions that the isolator can’t handle.

Is there a way for me to change what the nano advertises as its supported HDMI version to 1.3a? It seems like it must be configured somewhere, but I can’t find anything anywhere on where that lives.

Hi,

Could you share more specific detail about what kind frame rate or resolution we are talking about here?

Also, what does that HDMI isolator support? I am not sure about the device here. Is your “HDMI isolator” also providing its own edid to jetson nano?

HDMI 1.3 supports up to 10.2 Gb/s. At 8 bits per color and 60 Hz, a 1920x1080 display needs about 2.9 Gb/s. Whereas a 3840x2160 monitor with the same color depth and frame rate uses nearly 12 Gb/s. This is supported in HDMI 2, but not HDMI 1.3.

The isolator is just providing electrical isolation. It doesn’t change the signal itself, and doesn’t communicate with either end directly. That’s the reason I have this problem. It’s limited to the 10.2 Gb/s of HDMI 1.3a.

Hi,

Sorry that we didn’t have any other users reporting such issue. Actually, I am not sure what is that HDMI isolator is for.

Could you clarify what is the exact mechanism of that HDMI isolator? How does it connect to jetson nano and what is the expect result you want to see?

Here’s a link to an HDMI isolator. You can think of it as a special HDMI cable. It’s purely passive.

The question I have is about changing the version of HDMI that the nano will use. That’s got to be somewhere in the kernel or the graphics driver somewhere.

Hi,

Sorry that, actually our driver does not have such “option” to explicitly switch between HDMI 1.3/1.4 or 2.0.

If you ever read jetson’s display kernel driver code, you will notice

  1. Actually, Jetson nano/ Jetson TX2-NX and Jetson NX are all using the same driver code “hdmi2.0.c”.

  2. The difference is t210 (nano/tx1) SoC series platform will have different call flow in driver.

  3. But the different call in (2) is also not directly related to hdmi2.0/hdmi1.4 switch. It is more like SoC difference. For example, the method to set parent clock is different.

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