Incorrect CLOCK_HIGH assessment
I have a LG 4k monitor that works just fine on HDMI under Windows, but when I connect it under Linux, I only get FHD resolution.
I ran my kernel with drm.debug=0xe
and it produced the log I attached, as well as the following message about the modeline it should be using:
May 25 12:01:31 wmertens-nixos kernel: [drm:drm_mode_debug_printmodeline [drm]] Modeline "3840x2160": 30 297000 3840 4016 4104 4400 2160 2168 2178 2250 0x40 0x9
May 25 12:01:31 wmertens-nixos kernel: [drm:drm_mode_prune_invalid [drm]] Not using 3840x2160 mode: CLOCK_HIGH
When I use this modeline under Xorg by adding it with xrandr
, it works just fine. Somehow drm is too conservative on the allowed clocks.