[Intel-gfx] Screen distortion when changing resolution

[dolphinling]

Sometimes, when changing screen resolution, my screen "breaks". It does so in 
the following manner:

If the mouse cursor is in the bottom left corner, the whole screen vibrates left 
and right a short distance, at a fairly high frequency, with different rows of 
pixels moving different directions (it gives an effect that almost looks like 
interlacing).

If the mouse cursor is moved up, but still on the left side of the screen, the 
same vibrating effect occurs, but only the part of the screen higher than the 
cursor is displayed. Everything below the cursor is black.

If the mouse cursor moves right, but still on the bottom of the screen, the 
whole screen starts sliding left, looping around so that the left part of the 
screen is on the right. If the cursor is only a short distance from the corner, 
the movement is rather slow. If the cursor is moved back to the corner, the 
sliding stops, leaving the screen wrapped around. If the cursor is moved farther 
right, the sliding speeds up, going faster and faster the farther right the 
cursor is, until at about 3/8ths of the way across it is moving fast enough that 
it looks like it is going backwards and at 1/2 way across the movement stops, 
presumably because it is sliding around at exactly 1 rotation per screen 
refresh. Moving right more, it starts rotating again, fastest at 3/4 of the way 
across, backwards beyond that, and not rotating when the mouse is in the lower 
right corner.

Throughout this the vibration continues. The mouse still works, and clicking on 
things or hovering over them produces the correct response for what should be 
under the cursor. Also, there appears to be some leeway for where the cursor is. 
The sliding does not start until the cursor is a short ways away from the corner 
(how many pixels?). Similarly, in the center the region where the image does not 
move is multiple pixels wide.

If the cursor is moved away from all edges of the screen, all the effects occur: 
it vibrates, slides around, and only the top part of the screen is visible.

Restarting X does not fix the problem; I have to reboot to fix it. The virtual 
terminals work fine during this time though (using fbcon).

The system is an 845G, with kernel 2.6.32.3, libdrm 2.4.17, xorg-server 1.7.4, 
and xf86-video-intel from git. The problem has been occurring for a long time, 
if memory serves (though it could be wrong!) since UMS and XAA. It does seem to 
be less frequent than it used to, though (to the point that I used to be afraid 
to change my resolution, but now am not afraid, just annoyed when I hit it).

If I think of anything else about this problem, I'll mention it. If there's 
anything else you need to know, just ask.

-- 
dolphinling
<http://dolphinling.net/>