[ltp] Re: Unstable Radeon output at 1920x1200

[Alex Deucher]

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On Mon, Mar 24, 2008 at 4:24 PM, Alex Deucher <alexdeucher@gmail.com> wrote:
>
> On Mon, Mar 24, 2008 at 3:01 PM, Shem Multinymous <multinymous@gmail.com> wrote:
>  > Hi,
>  >
>  >  I have a problem driving LCD monitors at 1920x1200 via DVI on my T43
>  >  with Radeon X300. The image shows up, but is unstable: at erratic
>  >  times but generally once per 20-60 seconds, I get two disruptive
>  >  effects: the image disappears for a couple of seconds, or there is a
>  >  momentary image tearing effect. Basically, it looks like the monitor
>  >  is temporarily losing sync with the DVI signal. This occurs with 3
>  >  different LCD monitors and 3 different DVI cables.
>  >  Now, I know 1920x1200 24bpp is pushing the limit of DVI, but here's
>  >  the thing: when dual-booting into Windows, the display is rock-solid
>  >  at 1920x1200 24bpp DVI, using exactly the same hardware.
>  >
>  >  This is reproducible on my setup. I'm running Fedora 8's Xorg 6.8.0,
>  >  and relying on EDID ("xrandr --output DVI-0 --auto", no modelines or
>  >  frequency limits in xorg.conf). Xorg's EDID detection log is attached.
>  >
>  >  There's a related effect with the VGA output: at 1920x1200 with a
>  >  particular Dell monitor, X.org's output causes a weird "pixels
>  >  jiggling around" effect, but again Windows looks stable. This analog
>  >  effect is more subtle and variable, so I'm not 100% sure that the
>  >  difference between Windows and Linux is not a coincidence.
>  >
>  >  Is this just a matter of getting Xorg to use a better modeline, or
>  >  something deeper such as misconfigured Radeon CRTC registers?
>
>  Please attach your full Xorg log, thanks.

Sounds similar to bug 15175.  Does this patch help?
I suspect the monitor may prefer slightly different dividers for the
pll.  Even though they get to the same clock, some monitors seem to
prefer different dividers combinations.

Alex

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