That’s better.
Yes. Have to reboot or restart desktop-manager to use changed xorg.conf.
The 60Hz 4K modeline shows up now.
It is rejected:
[ 8.859] (WW) NVIDIA(GPU-0): Mode is rejected: DP Bandwidth check failed.
[ 8.859] (WW) NVIDIA(GPU-0): GPU extended capability check failed.
[ 8.859] (WW) NVIDIA(GPU-0): Mode “3840x2160_60” is invalid.
Must have decided the DP link number is to small or GPU is too slow.
1000s of lines of debug cruft / info & the driver makes no mention of the GPU extended capability check.
Maybe have to find another magic debug option keyword or:
Option “ModeValidation” “GPU-0: NoExtendedGpuCapabilitiesCheck”
Option “ModeValidation” “GPU-0.DFP-3: NoExtendedGpuCapabilitiesCheck” ???
or “GPU-0.DFP-3: NoDisplayPortBandwidthCheck”
The driver docs does not show option cmd construct for " CapabilityCheck" so may or may not have the port DP-0 or monitor DFP-3.
The 30Hz 4K modeline invalidates the EDID vertical freq (refresh rate):
[ 8.858] (II) NVIDIA(GPU-0): The EDID for DELL U2718Q (DP-0) contradicts itself: mode
[ 8.858] (II) NVIDIA(GPU-0): “3840x2160” is specified in the EDID; however, the EDID’s
[ 8.858] (II) NVIDIA(GPU-0): valid VertRefresh range (49.000-86.000 Hz) would exclude
[ 8.858] (II) NVIDIA(GPU-0): this mode’s VertRefresh (29.981 Hz); ignoring VertRefresh
[ 8.858] (II) NVIDIA(GPU-0): check for mode “3840x2160”.
but it uses it anyway!