In the release notes of 319.23 (http://www.nvidia.co.uk/object/linux-display-amd64-319.23-driver-uk.html) it says:
“Added support for HDMI 4K resolutions. Using a 4K resolution with an HDMI display requires a Kepler or later GPU.”
We tested an ASUS Titan 6GD5 with 319.32 (and 325.08) on Linux 64-bit (Ubuntu 12.10, X.org 1.13.0) with a Sony Bravia X9005 55" screen and its bigger 65" brother. This was using an HDMI cable, we made sure it was a high-speed cable. In no way could we get the Titan to detect a resolution higher than 1920x1080.
This was in an electronics store, so we couldn’t do endless tests, but there was a local Windows demo machine with a Radeon 7700 that managed to do 3840x2160 on the 55" screen without problems. We didn’t test with our system under Windows as it was Linux only (and our preferred OS). We also didn’t test yet with forcing e.g. 3840x2160@24.
Did something change in the driver since 319.23 that disables 4k over HDMI? What screen was used to certify the 4k-over-hdmi capability in the first place? Any other tricks we might try?