The ADV7604 has internal EDID RAM. You have to configure that portion along the way of configuring other things for this chip (like matrices, output format, etc). I hope you connected the DDC lines between the source and the decoder, in order to have the channel to pull the edid information.
In the “old days”, before automatic query of monitors (meaning anything VGA) a driver disk was included with each monitor. The name “driver disk” is misleading, it isn’t a driver at all…it is a list of the monitor’s specs which drivers can use. In the Linux side of this the X11 server needs a “modeline”, and the driver disk used timing specs of the monitor to create this modeline. You will essentially need to find a modeline compatible with your monitor, and then turn it into EDID…followed by putting EDID into a ROM or other adapater. Some information about this process: https://kodi.wiki/view/Creating_and_using_edid.bin_via_xorg.conf https://en.wikipedia.org/wiki/XFree86_Modeline
Keep in mind that you cannot use a modeline within a Jetson…the information there must be from EDID or it won’t be accepted. On the other hand, you can work on a desktop system which does work with a modeline and create/test the modeline there. With that modeline you can create the EDID, check it out in http://www.edidreader.com, and then program it into your adapter.
The easiest way to get to craft an edid magic binary is to use for example the DELTACAST EDID editor. You can load the edid from the connected HDMI monitor, then modify the interface portion to disable HD resolutions. There you get your 128 or 256 magic bytes, which are to be loaded to the ADV chip’s EDID RAM.
If you need any assistance, i can provide support, since I have designed quite a few HDMI interfaces (yet digital only, from hdmi input to eDP, DP or MIPI DSI output for display).
The issue with SD analog video would be that we have no confirmation whether the TX2 can support interlaced modes, since for analog you would definitely need that (480i or 576i is SD).
EDID was made for VGA and then adapted to DVI and HDMI. The original version had a bitmap for supported resolutions - like vga, svga, xga. Then some extensions allowed to describe custom resolutions (I use those, for my 1080 x 1920 phone screen adaptor for HDMI). But that is still a PC world, with progressive screens.
With HDMI coming into to game, which is a consumer video standard intended for 422 video signals, not for PC monitors, a way to specify resolution is by means of CEA extensions to the EDID. These fields hold the information about the supported VIDEO modes (not PC resolutions), like 1080i, 1080p, 720p, 480p, 480i, etc…
So to properly craft a SD video EDID, you have to definitely have some CEA extension (which is the part above the basic 128 byte block). P
How to do it? Please download the DELTACAST edid editor (or any other editor) and pull-in an EDID from a HDMI port of a TELEVISION (not a PC monitor). You shall see those extensions. Then you can uncheck those resolutions which you do not want (HD ones and progressive 480p/576p).