[Bug 9714] Radeon driver doesn't produce stable image on external display

bugzilla-daemon at annarchy.freedesktop.org bugzilla-daemon at annarchy.freedesktop.org
Sat Jan 20 14:05:17 PST 2007

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------- Additional Comments From sroland at tungstengraphics.com  2007-01-20 14:05 -------
(In reply to comment #0)
> The display works fine when using OS/x or an older powerbook with a Radeon 9000
> card instead of the Mobility Radeon 9600 M10.  The display is connected via VGA,
> since the driver currently doesn't support DVI. My X.org version is 7.1.0.  Two
> weeks ago I compiled the newest driver from git, but the result was the same.
I assume when you say it doesn't happen with OS/X then you're using also VGA output?

> I've tried every possible configuration I could think of that were capable of
> driving the external display. The attached config contains some extra
> information about the various things I tried (N.B. the exact same config works
> on another powerbook with the radeon 9000 card). The most notable is the fact
> that switching the explicit modelines on does really improve the overall
> quality. When I let X decide not even 1024x768 is stable, and the resolutions
> above that are a lot worse. When I do enable the modelines the amount of
> disturbance lessens in every resolution. In 1024x768 it even causes the image to
> be totally clear.
It is not surprising the reduced blanking modelines help, since vga outputs from
notebooks are known to be generally not really good enough for clear output in
high resolutions (though I don't know how well apple or specifically this
notebook does). (And in fact the pixel clock is above the monitor's advertized
maximum without it in 1920x1200).
I'd have said it's just a not very high quality vga output, maybe coupled with a
cable which degrades signal quality further, and the input circuitry in the
monitor could make a difference too. However, if this works with OS/X, it
apparently must be something else as timings used by OS/X are likely the same
(though I'm not sure about sync polarity). I'll wonder, is it possible that
using "wrong" reference divider etc. degrades signal quality (as those are
defaulted since obviously your chip doesn't have a pc bios)? Might be something
else though.          
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