Comment 2 for bug 1896186

From the Pi's config.txt docs at https://www.raspberrypi.org/documentation/configuration/config-txt/video.md :

  "The hdmi_pixel_encoding command forces the pixel encoding mode. By default, it will use the mode requested from the EDID, so you shouldn't need to change it."

Which would suggest that if the wrong encoding is being selected for your monitor, then it's because your monitor is transmitting the wrong information in its EDID. However, the table below that states that the default is "RGB limited for CEA, RGB full for DMT" which suggests (to me at least) that the heuristic is rather simpler and that any CEA (TV) mode gets the limited 16-235 range (which is typical for TVs), while any DMT (monitor) mode gets the full 0-255 range.

It might be useful to query what EDID the Pi is getting from your monitor. I don't *think* this works when the KMS overlay is loaded, but if you boot the server image, install "libraspberrypi-bin" on it, then run "tvservice -d edid.dat" that should dump the EDID the pi's firmware received from your monitor. If you could attach that we could take a look at what might be going on?