[Bug 86462] [DP MST?] 4k monitor at 48hz leads to blank screen

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=86462

--- Comment #14 from Clinton Taylor <clinton.a.taylor at intel.com> ---
   On a BDW i7 based system there doesn't appear to be a problem with 1920x2400
48Hz SST or MST. I am able to display in both SST and through an MST hub to my
Planar 4K ix2850 monitor. 

   I don't have an IBM T221 DG5 to test this on, but the limitation does not
appear to be the i915 driver. This could be a limitation of the Dell port
replicator using a 245 MHz pixel clock. 

Here is the xrandr output through an MST hub at 1920x2400 48 Hz.

Screen 0: minimum 8 x 8, current 1920 x 2400, maximum 32767 x 32767
DP1 disconnected (normal left inverted right x axis y axis)
   1920x2400_32.00  31.97  
   1920x2400_48.00  47.98  
DP1-1 connected primary 1920x2400+0+0 (normal left inverted right x axis y
axis) 621mm x 341mm
   3840x2160     60.00 +  30.00    29.97  
   1920x2400     47.98* 
   1920x2160     60.00  
   2560x1440     59.95  
   1920x1440     60.00  
   2048x1152     60.00  
   1920x1200     59.88  
   1920x1080     60.00    50.00    59.94    24.00    23.98  
   1600x1200     60.00  
   1680x1050     59.95  
   1600x900      60.00  
   1280x1024     75.02    60.02  
   1152x864      75.00  
   1280x720      60.00    50.00    59.94  
   1024x768      75.08    70.07    60.00  
   832x624       74.55  
   800x600       72.19    75.00    60.32    56.25  
   720x576       50.00  
   720x480       60.00    59.94  
   640x480       75.00    72.81    66.67    60.00    59.94  
   720x400       70.08  
   1920x2400_48.00  47.98  

newmode commands used to add 32 and 48 Hz 1920x2400 modes:
xrandr --newmode "1920x2400_48.00"  245.000 1920 1968 2000 2080 2400 2402 2412
2455 -hsync +vsync

xrandr --newmode "1920x2400_32.00"  202.75  1920 2056 2256 2592  2400 2403 2413
2447 -hsync +vsync

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