Pixelation of red text on GTX 970/4K@60Hz specific to single monitor

Hi,

I have had a GTX 970 for a long while now with no issues. I’m running Ubuntu 17.04 on Kernel 4.10. I’ve recently acquired a 4K monitor (X4071UHSU-B1) which is capable of 4K@60Hz over HDMI 2.0.

For the avoidance of doubt, I’ve reproduced this issue with multiple HDMI cables rated to 4K@60Hz (one purchased specially to eliminate this variable).

I was initially unable to use 4K@60Hz, but this post: https://devtalk.nvidia.com/default/topic/939971/4k-60hz-works-in-windows-not-in-linux-workaround-found-/?offset=29 enabled me to do so. However, I’m now confronted with another issue - any and all red pixels on the screen become pixelated. The results of this are as follows:

https://imgur.com/a/xrIUW

As can be seen, pixelation only occurs for red pixels, is specific to my 4K monitor, and disappears at 30Hz. I’m quite stumped by this issue - I attach my bug report log (edit: there doesn’t seem to be an option to upload, so https://www.dropbox.com/s/eg1m34vnwdnp31g/nvidia-bug-report.log.gz?dl=0).

The images illustrate only the most obvious example - but the effects are visible on almost any screen as a slight un-focusing of all of the on screen elements - due, I presume, to most of them having some amount of red on them.

Does the monitor show what resolution/mode it is currently connected at? It almost seems as if it’s connected using YUV 422 or 420 rather than RGB.

The closest I can get is this - but it doesn’t show anything that I can recognise as strange,
unfortunately: https://www.dropbox.com/s/iu8aaezd6518cmr/2017-06-18%2011.58.59.jpg?dl=0

You’re using a custom edid for a LG TV, probably from the post you mentioned. Don’t do that. Why couldn’t you use the edid from your monitor?