[Bug 22333] Sudden screen blanks

[bugzilla-daemon at freedesktop.org]

http://bugs.freedesktop.org/show_bug.cgi?id=22333





--- Comment #3 from Alex Deucher <agd5f at yahoo.com>  2009-07-02 23:56:06 PST ---
(In reply to comment #1)
> I can confirm this behavior. Happens at least with xf86-video-ati versions 6.8
> to 6.12.2, xorg server versions 1.3.0 to 1.5.3, running an r250 chip on a
> Thinkpad T40/T41 with 32-64 MB of vram. While driving both internal LVDS and an
> external DVI, and under heavy video load (easiest way to reproduce is to scroll
> a large window) the DVI would go blank as described.

It's probably underflow to the crtc in your case.  Digital monitors like DVI
tend to be more sensitive to disruptions in the data flow.  The display
controllers are contending with the drawing engine for memory bandwidth. 
maleadt's issue is different.

> 
> Few more facts: neither an LVDS nor an external VGA driven by the same crtc go
> blank (only the DVI does). Blanking only happens with hardware acceleration. It
> does not happen when more vram is present (tested on a T42), so it looks as if
> this is related to vram allocation or bandwidth problem. It does not happen on
> lower resolution modes, specifically when the DVI resolution does not exceed
> the LVDS one.  Tried prioritizing video bus in several different ways, to no
> avail.

A t42 with an rv350 is a faster chip with more memory bandwidth available than
your rv250.  Additionally, IBM only rates the DVI port on the dock to
1280x1024 at 60hz, while you were attempting to run a much larger mode IIRC.  The
underflow did not happen at lower res modes.  I think you are hitting bandwidth
limits of your setup so this isn't really a bug but a hardware limitation in
your case.  


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