Comment # 6 on bug 40699 from Maciej Pawlik

I've done some testing, and vanilla kernel works only with 720x400. With
ATOM_DP_SS_ID2, as you suggested, some modes work, some don't:
DisplayPort-0 connected 1680x1050+0+0 (normal left inverted right x axis y
axis) 518mm x 324mm
   1920x1200      60.0 + <-ok
   1920x1080      60.0   <-ok
   1600x1200      60.0   <-ok
   1680x1050      60.0*  <-ok
   1280x1024      60.0   <-can't sync
   1280x960       60.0   <-can't sync
   1024x768       60.0   <-ok
   800x600        60.3   <-can't sync
   640x480        60.0   <-can't sync
   720x400        70.1   <-ok

It's the same with my crude fix.