[Bug 68718] [snb] vsync hang

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=68718

--- Comment #28 from Ilia Mirkin <imirkin at alum.mit.edu> ---
(In reply to comment #27)
> (In reply to comment #26)
> > Another oddity:
> > 
> > 	/* Always program one less than the desired value */
> > 	if (--y1 < 0)
> > 		y1 = crtc->bounds.y2;
> > 
> > ...
> > 
> > 	if (y2 == y1)
> > 		return false;
> > 
> > Should that perhaps be if (y2 < y1)?
> 
> It's actually legal for y2 to be less than y1 - e.g. any window that starts
> on the top line.

Oh, because it does it in a circular fashion, so 1 less than 0 is back to the
bottom?

One last question... what makes you think it's this code that's causing issues?
i.e. what do I look at in the hang to work that out (so that I can go and try
100 diff things and make sure that this is the place where things are hanging).

Also -- I don't know what kind of resources you have available, but I don't
exactly have a "rare" hardware setup. Lenovo T420s laptop, internal LVDS panel,
and either a VGA or HDMI-connected 1920x1200 screen depending on where I am
(and I'm pretty sure the second screen doesn't actually play a part here). 

Load up chrome and go to google maps (I think the reason I was having trouble
getting it to hang earlier was that they had for some reason temporarily turned
off Earth mode... now that it's back, it hangs on load again) or that webgl
demo.

Is the suggestion that this is hard to reproduce and I'm in a (relatively)
unique configuration/setup/etc? Or are lots of people seeing this, which makes
it no easier to figure out what's going on?

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