[Bug 32316] Severe glitches with KMS + external monitor

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=32316

--- Comment #10 from Alex Deucher <agd5f at yahoo.com> 2010-12-17 07:26:38 PST ---
(In reply to comment #9)
> There is one point that I should perhaps amplify: when I boot with the external
> monitor attached, X comes up in 1024x768 mode. Even in KMS, it works fine at
> this resolution. The glitches only start when I try to change to a higher
> resolution (LVDS 1400x1050, VGA 1920x1080). I have not tried many different
> higher-resolution settings, just these.

Right, the glitches are bandwidth related, the memory controller is having
trouble keeping up with all the requests so you end up with underflow to the
VGA port.  Either there's a problem with the display watermarks (which
shouldn't be a factor with disp_priority set to 2), or the bandwidth requests
are too much for the asic to keep up with.  You might try a lower color depth. 
You might also try:
Option "EXAPixmaps" "off"
in the device section of your xorg.conf

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