5.3.0-rc6: i915 fails at typec_displayport 5120x1440

[Leho Kraav]

Hardware: Dell Latitude 7400 2-in-1, Whiskey Lake, Intel 620

5120x1440 fails to display.

Next available mode 3840x1080 displays fine.

Is this a kernel, or a driver level issue? It fails both in Xorg and
Wayland, so seems something at the lower levels. This 49" monitor worked
fine on Latitude 7480 (Kaby Lake), so I'm thinking something with `i915`
module layer.

What should I try next?

```
leho@papaya ~ $ [-] uname 
Linux papaya 5.3.0-rc6+gentoo+ #95 SMP PREEMPT Mon Aug 26 23:50:08 EEST 2019 x86_64 Intel(R) Core(TM) i5-8365U CPU @ 1.60GHz GenuineIntel GNU/Linux

leho@papaya ~ $ [-] xrandr 
Screen 0: minimum 8 x 8, current 5120 x 1440, maximum 32767 x 32767
...
DP1 disconnected (normal left inverted right x axis y axis)
DP2 connected primary 3840x1080+0+0 (normal left inverted right x axis y axis) 1200mm x 340mm
   5120x1440     59.98 +  29.98  
   3840x1080     59.97*+
   2560x1080     60.00    59.94    59.98  
   1920x1080     60.00    60.00    50.00    59.94  
   1920x1080i    60.00    50.00    59.94  
   1600x1200     60.00  
   1280x1024     75.02    60.02  
   1280x800      59.81  
   1152x864      75.00  
   1280x720      60.00    50.00    59.94  
   1024x768      75.03    60.00  
   800x600       75.00    60.32  
   720x576       50.00  
   720x480       60.00    59.94  
   640x480       75.00    60.00    59.94  
   720x400       70.08  
HDMI1 disconnected (normal left inverted right x axis y axis)
HDMI2 disconnected (normal left inverted right x axis y axis)
VIRTUAL1 disconnected (normal left inverted right x axis y axis)

leho@papaya ~ $ [-] xrandr --output DP2 --mode 5120x1440 --verbose
crtc 0:    5120x1440  59.98 +0+0 "DP2"
xrandr: Configure crtc 0 failed
crtc 0: disable
crtc 1: disable
crtc 2: disable
crtc 3: disable
screen 0: revert
crtc 0: revert
crtc 1: revert
crtc 2: revert
crtc 3: revert
```

-- 
Leho Kraav, senior technology & digital marketing architect