screen update problems with Intel HD 4600 + virtual screen

[Krzysztof Halasa]

khalasa at piap.pl (Krzysztof Hałasa) writes:

> I'm having screen update problems problems with an Intel HD 4600 with
> panning + virtual screen. Fedora 20 + updates, CPU is Core i7 4770K,
> I'm using xrandr --output HDMI1 --panning 4096x2404. The physical screen
> size is 1920x1200.
> Another setup also experiencing this problem is Core i5 4200M with
> a 1600x900 physical screen (LVDS) and (a bit larger) virtual screen
> (again with panning).

This happens with both UXA and SNA. ATM I'm now using SNA as UXA(?) had
some probably unrelated problems with Xvideo (non)updates.

Screen 0: minimum 320 x 200, current 4096 x 2404, maximum 32767 x 32767
VGA1 disconnected (normal left inverted right x axis y axis)
HDMI1 connected 4096x2404+0+0 (normal left inverted right x axis y axis)
518mm x 324mm panning 4096x2404+0+0
   1920x1200     59.95*+
   [etc.]
DP1 disconnected (normal left inverted right x axis y axis)
HDMI2 disconnected (normal left inverted right x axis y axis)
HDMI3 disconnected (normal left inverted right x axis y axis)

It looks with SNA, all is good as long as the screen isn't moved
(panned) down more than 7 pixels (i.e. the screen y offset must be 0 - 7
and x offset doesn't matter):

switch to mode 1920x1200 at 60.0 on pipe 0 using HDMI1, position (2176, 0), rotation normal
switch to mode 1920x1200 at 60.0 on pipe 0 using HDMI1, position (2176, 1), rotation normal
switch to mode 1920x1200 at 60.0 on pipe 0 using HDMI1, position (2176, 2), rotation normal
...
switch to mode 1920x1200 at 60.0 on pipe 0 using HDMI1, position (2176, 6), rotation normal
switch to mode 1920x1200 at 60.0 on pipe 0 using HDMI1, position (2176, 7), rotation normal

Now I scroll down 1 pixel:
switch to mode 1920x1200 at 60.0 on pipe 0 using HDMI1, position (2176, 8), rotation normal

and immediately screen isn't updated correctly. For example, an
application window is created normally, but when I move it (the app
window) down, the top part of the window, max 8 pixels, is left on the
screen (the moved window is ok). It almost looks like the code somewhere
adds the vertical screen offset twice.

Panning the screen again fixes the display again. Creating new windows
and other events may also fix it.

Nobody using virtual screen anymore? ;-)

I can provide all kinds of debug logs etc. of course.
-- 
Krzysztof Halasa